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Palmoplantar keratoderma (PPK) are debilitating lesions that arise in individuals with pachyonychia congenita (PC) and feature upregulation of danger-associated molecular patterns and skin barrier regulators. The defining features of PC-associated PPK are reproduced in mice null for keratin 16 (Krt16), which is commonly mutated in PC patients. Here, we have shown that PPK onset is preceded by oxidative stress in footpad skin of Krt16-/- mice and correlates with an inability of keratinocytes to sustain nuclear factor erythroid-derived 2 related factor 2-dependent (NRF2-dependent) synthesis of the cellular antioxidant glutathione (GSH). Additionally, examination of plantar skin biopsies from individuals with PC confirmed the presence of high levels of hypophosphorylated NRF2 in lesional tissue. In Krt16-/- mice, genetic ablation of Nrf2 worsened spontaneous skin lesions and accelerated PPK development in footpad skin. Hypoactivity of NRF2 in Krt16-/- footpad skin correlated with decreased levels or activity of upstream NRF2 activators, including PKCδ, receptor for activated C kinase 1 (RACK1), and p21. Topical application of the NRF2 activator sulforaphane to the footpad of Krt16-/- mice prevented the development of PPK and normalized redox balance via regeneration of GSH from existing cellular pools. Together, these findings point to oxidative stress and dysfunctional NRF2 as contributors to PPK pathogenesis, identify K16 as a regulator of NRF2 activation, and suggest that pharmacological activation of NRF2 should be further explored for PC treatment.

Small interfering RNAs (siRNAs) specifically and potently inhibit target gene expression. Pachyonychia congenita (PC) is a skin disorder caused by mutations in genes encoding keratin (K) 6a/b, K16, and K17, resulting in faulty intermediate filaments. A siRNA targeting a single nucleotide, PC-relevant mutation inhibits K6a expression and has been evaluated in the clinic with encouraging results. To better understand the pathophysiology of PC, and develop a model system to study siRNA delivery and visualize efficacy in skin, wild type (WT) and mutant K6a complementary DNAs (cDNAs) were fused to either enhanced green fluorescent protein or tandem tomato fluorescent protein cDNA to allow covisualization of mutant and WT K6a expression in mouse footpad skin using a dual fluorescence in vivo confocal imaging system equipped with 488 and 532 nm lasers. Expression of mutant K6a/reporter resulted in visualization of keratin aggregates, while expression of WT K6a/reporter led to incorporation into filaments. Addition of mutant K6a-specific siRNA resulted in inhibition of mutant, but not WT, K6a/reporter expression. Intravital imaging offers subcellular resolution for tracking functional activity of siRNA in real time and enables detailed analyses of therapeutic effects in individual mice to facilitate development of nucleic acid-based therapeutics for skin disorders.

Pachyonychia congenita (PC) is a skin disorder resulting from mutations in keratin (K) proteins including K6a, K6b, K16, and K17. One of the major symptoms is painful plantar keratoderma. The pathogenic sequelae resulting from the keratin mutations remain unclear.To better understand PC pathogenesis.RNA profiling was performed on biopsies taken from PC-involved and uninvolved plantar skin of seven genotyped PC patients (two K6a, one K6b, three K16, and one K17) as well as from control volunteers. Protein profiling was generated from tape-stripping samples.A comparison of PC-involved skin biopsies to adjacent uninvolved plantar skin identified 112 differentially-expressed mRNAs common to patient groups harboring K6 (i.e., both K6a and K6b) and K16 mutations. Among these mRNAs, 25 encode structural proteins including keratins, small proline-rich and late cornified envelope proteins, 20 are related to metabolism and 16 encode proteases, peptidases, and their inhibitors including kallikrein-related peptidases (KLKs), and serine protease inhibitors (SERPINs). mRNAs were also identified to be differentially expressed only in K6 (81) or K16 (141) patient samples. Furthermore, 13 mRNAs were identified that may be involved in pain including nociception and neuropathy. Protein profiling, comparing three K6a plantar tape-stripping samples to non-PC controls, showed changes in the PC corneocytes similar, but not identical, to the mRNA analysis.Many differentially-expressed genes identified in PC-involved skin encode components critical for skin barrier homeostasis including keratinocyte proliferation, differentiation, cornification, and desquamation. The profiling data provide a foundation for unraveling the pathogenesis of PC and identifying targets for developing effective PC therapeutics.

Summary This is a report of the research presented at the 11th Annual Meeting of the International Pachyonychia Congenita Consortium, held on 6 May 2014 in Albuquerque, NM, U.S.A. This year's meeting was divided into five corners concerning pachyonychia congenita (PC) research: (i) ‘PC Pathogenesis Cornered’, an overview of recent keratin research, for PC and other skin disorders; (ii) ‘From All Corners of …’, an outline of other genetic disorders that we can learn from; (iii) ‘Fighting For Our Corner’, an outline of National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases programmes and U.S. funding opportunities applicable to rare skin disorders; (iv) ‘The PC Corner’, focusing on recent clinical studies related to PC; and (v) ‘Clinical Corners: Turning the Corner?’, an update on ongoing PC clinical trials.

The International Pachyonychia Congenita Consortium (IPCC) was founded in 2004 in Park City, Utah, USA. Its goal is to find a cure for pachyonychia congenita, a rare keratinizing disorder. From February 14th–17th, 2013, the group convened in Park City for their tenth annual meeting. The 2013 meeting focused on how to best move forward with clinical trials and on learning from work in other scientific areas, with an emphasis on understanding mechanisms of pain and hyperkeratosis. Considerable time was spent on discussing the best way to move forward with development of new treatments and how to obtain or develop tools that can measure treatment outcomes in PC.

The development of siRNA-based gene silencing therapies has significant potential for effectively treating debilitating genetic, hyper-proliferative or malignant skin conditions caused by aberrant gene expression. To be efficacious and widely accepted by physicians and patients, therapeutic siRNAs must access the viable skin layers in a stable and functional form, preferably without painful administration. In this study we explore the use of minimally-invasive steel microneedle devices to effectively deliver siRNA into skin. A simple, yet precise microneedle coating method permitted reproducible loading of siRNA onto individual microneedles. Following recovery from the microneedle surface, lamin A/C siRNA retained full activity, as demonstrated by significant reduction in lamin A/C mRNA levels and reduced lamin A/C protein in HaCaT keratinocyte cells. However, lamin A/C siRNA pre-complexed with a commercial lipid-based transfection reagent (siRNA lipoplex) was less functional following microneedle coating. As Accell-modified “self-delivery” siRNA targeted against CD44 also retained functionality after microneedle coating, this form of siRNA was used in subsequent in vivo studies, where gene silencing was determined in a transgenic reporter mouse skin model. Self-delivery siRNA targeting the reporter (luciferase/GFP) gene was coated onto microneedles and delivered to mouse footpad. Quantification of reporter mRNA and intravital imaging of reporter expression in the outer skin layers confirmed functional in vivo gene silencing following microneedle delivery of siRNA. The use of coated metal microneedles represents a new, simple, minimally-invasive, patient-friendly and potentially self-administrable method for the delivery of therapeutic nucleic acids to the skin.

The International Pachyonychia Congenita Consortium (IPCC) is a group of physicians and scientists from around the world dedicated to developing therapies for pachyonychia congenita, a rare autosomal dominant skin disorder. The research presented at the 13th Annual Research Symposium of the IPCC, held on 10-11 May 2016, in Scottsdale, AZ, U.S.A., is reported here.

Monogenic skin diseases arise from well-defined single gene mutations, and in some cases a single point mutation. As the target cells are superficial, these diseases are ideally suited for treatment by nucleic acid-based therapies as well as monitoring through a variety of noninvasive imaging technologies. Despite the accessibility of the skin, there remain formidable barriers for functional delivery of nucleic acids to the target cells within the dermis and epidermis. These barriers include the stratum corneum and the layered structure of the skin, as well as more locally, the cellular, endosomal and nuclear membranes. A wide range of technologies for traversing these barriers has been described and moderate success has been reported for several approaches. The lessons learned from these studies include the need for combinations of approaches to facilitate nucleic acid delivery across these skin barriers and then functional delivery across the cellular and nuclear membranes for expression (e.g., reporter genes, DNA oligonucleotides or shRNA) or into the cytoplasm for regulation (e.g., siRNA, miRNA, antisense oligos). The tools for topical delivery that have been evaluated include chemical, physical and electrical methods, and the development and testing of each of these approaches has been greatly enabled by imaging tools. These techniques allow delivery and real time monitoring of reporter genes, therapeutic nucleic acids and also triplex nucleic acids for gene editing. Optical imaging is comprised of a number of modalities based on properties of light-tissue interaction (e.g., scattering, autofluorescence, and reflectance), the interaction of light with specific molecules (e.g., absorbtion, fluorescence), or enzymatic reactions that produce light (bioluminescence). Optical imaging technologies operate over a range of scales from macroscopic to microscopic and if necessary, nanoscopic, and thus can be used to assess nucleic acid delivery to organs, regions, cells and even subcellular structures. Here we describe the animal models, reporter genes, imaging approaches and general strategies for delivery of nucleic acids to cells in the skin for local expression (e.g., plasmid DNA) or gene silencing (e.g., siRNA) with the intent of developing nucleic acid-based therapies to treat diseases of the skin.

Development of RNA interference (RNAi)-based therapeutics has been hampered by the lack of effective and efficient means of delivery. Reliable model systems for screening and optimizing delivery of RNAi-based agents in vivo are crucial for preclinical research aimed at advancing nucleic acid-based therapies. We describe here a dual fluorescent reporter xenograft melanoma model prepared by intradermal injection of human A375 melanoma cells expressing tandem tomato fluorescent protein (tdTFP) containing a small interfering RNA (siRNA) target site as well as enhanced green fluorescent protein (EGFP), which is used as a normalization control. Intratumoral injection of a siRNA specific to the incorporated siRNA target site, complexed with a cationic lipid that has been optimized for in vivo delivery, resulted in 65%±11% knockdown of tdTFP relative to EGFP quantified by in vivo imaging and 68%±10% by reverse transcription-quantitative polymerase chain reaction. No effect was observed with nonspecific control siRNA treatment. This model provides a platform on which siRNA delivery technologies can be screened and optimized in vivo.

Treatment of skin disorders with short interfering RNA (siRNA)-based therapeutics requires the development of effective delivery methodologies that reach target cells in affected tissues. Successful delivery of functional siRNA to the epidermis requires (1) crossing the stratum corneum, (2) transfer across the keratinocyte membrane, followed by (3) incorporation into the RNA-induced silencing complex. We have previously demonstrated that treatment with microneedle arrays loaded with self-delivery siRNA (sd-siRNA) can achieve inhibition of reporter gene expression in a transgenic mouse model. Furthermore, treatment of human cultured epidermal equivalents with sd-siRNA resulted in inhibition of target gene expression. Here, we demonstrate inhibition of CD44, a gene that is uniformly expressed throughout the epidermis, by sd-siRNA both in vitro (cultured human epidermal skin equivalents) and in vivo (full-thickness human skin equivalents xenografted on immunocompromised mice). Treatment of human skin equivalents with CD44 sd-siRNA markedly decreased CD44 mRNA levels, which led to a reduction of the target protein as confirmed by immunodetection in epidermal equivalent sections with a CD44-specific antibody. Taken together, these results demonstrate that sd-siRNA, delivered by microneedle arrays, can reduce expression of a targeted endogenous gene in a human skin xenograft model.

Epidermolytic palmoplantar keratoderma (EPPK) is one of >30 autosomal-dominant human keratinizing disorders that could benefit from RNA interference (RNAi)-based therapy. EPPK is caused by mutations in the keratin 9 (KRT9) gene, which is exclusively expressed in thick palm and sole skin where there is considerable keratin redundancy. This, along with the fact that EPPK is predominantly caused by a few hotspot mutations, makes it an ideal proof-of-principle model skin disease to develop gene-specific, as well as mutation-specific, short interfering RNA (siRNA) therapies. We have developed a broad preclinical RNAi-based therapeutic package for EPPK containing generic KRT9 siRNAs and allele-specific siRNAs for four prevalent mutations. Inhibitors were systematically identified in vitro using a luciferase reporter gene assay and validated using an innovative dual-Flag/Strep-TagII quantitative immunoblot assay. siKRT9-1 and siKRT9-3 were the most potent generic K9 inhibitors, eliciting >85% simultaneous knockdown of wild-type and mutant K9 protein synthesis at picomolar concentrations. The allele-specific inhibitors displayed similar potencies and, importantly, exhibited strong specificities for their target dominant-negative alleles with little or no effect on wild-type K9. The most promising allele-specific siRNA, siR163Q-13, was tested in a mouse model and was confirmed to preferentially inhibit mutant allele expression in vivo.

Pachyonychia congenita (PC), a rare autosomal-dominant keratin disorder caused by mutations in keratin genes KRT6A/B, KRT16, or KRT17, is characterized by painful plantar keratoderma and hypertrophic nail dystrophy. Available studies assessing oral retinoid treatment for PC are limited to a few case reports.We sought to assess overall effectiveness, adverse effects, and patient perspective in patients with PC receiving oral retinoids.In a questionnaire-based retrospective cross-sectional survey of 30 patient with PC assessing oral retinoids (10-50 mg/d for 1-240 months), we determined the clinical score, satisfaction score, visual analog pain scale, and adverse effects.In 50% of patients there was thinning of hyperkeratoses (average improvement 1.6 on a scale from -3 to +3) (95% confidence interval 1.2-1.9, P.001). In all, 14% observed amelioration of their pachyonychia; 79% did not experience any nail change. The self-reported overall satisfaction score with oral retinoid treatment was 2 or greater in 50% of the patients (mean 4.5 on a scale of 1-10). Although 33% reported decreased and 27% increased plantar pain with treatment, 40% did not notice any pain change. All patients experienced adverse effects, and 83% reported to have discontinued medication. Risk/benefit analysis favored lower retinoid doses (≤25 mg/d) over a longer time period (5 months), compared with higher doses (25 mg/d) for a shorter time (≤5 months).The retrospective, cross-sectional study design is prone to a recall bias.Oral retinoids are effective in some patients with PC. However, many patients discontinued medication because adverse effects outweighed the benefits. Careful dose titration is warranted in patients informed about potential adverse effects.

Small interfering RNA (siRNA) is a highly potent drug in gene-based therapy with a challenge of being delivered in a sustained manner. Nanoparticle drug delivery systems allow for incorporating and controlled release of therapeutic payloads. We demonstrate that solid lipid nanoparticles can incorporate and provide sustained release of siRNA. Tristearin solid lipid nanoparticles, made by nanoprecipitation, were loaded with siRNA (4.4–5.5 weight percent loading ratio) using a hydrophobic ion pairing approach that employs the cationic lipid DOTAP. Intradermal injection of these nanocarriers in mouse footpads resulted in prolonged siRNA release over a period of 10–13 days. In vitro cell studies showed that the released siRNA retained its activity. Nanoparticles developed in this study offer an alternative approach to polymeric nanoparticles for encapsulation and sustained delivery of siRNA with the advantage of being prepared from physiologically well-tolerated materials.

The International Pachyonychia Congenita Consortium (IPCC) is a group of physicians and scientists who have agreed to work together to develop therapeutics for the rare skin disorder pachyonychia congenita (PC). Each IPCC meeting is devoted to the most pressing issues related to developing PC therapeutics and to reach consensus on directions to achieve realistic goals. A list of IPCC members can be found on the organization’s website (http://www.pachyonychia.org), and details of the oral presentations at this year’s annual meeting are listed in Supplementary Table 1 online.

RNA interference (RNAi) is an evolutionarily conserved mechanism that results in specific gene inhibition at the mRNA level. The discovery that short interfering RNAs (siRNAs) are selective, potent, and can largely avoid immune surveillance has resulted in keen interest to develop these inhibitors as therapeutics. A single nucleotide-specific siRNA (K6a_513a.12, also known as TD101) was recently evaluated in a phase 1b clinical trial for the rare skin disorder, pachyonychia congenita (PC). To develop a clinical trial molecular end point for this type of trial, methods were developed to: (1) isolate total RNA containing amplifiable mRNA from human skin and callus material; (2) quantitatively distinguish the single-nucleotide mutant mRNA from wild-type K6a mRNA in both patient-derived keratinocytes and patient callus; and (3) demonstrate that repeated siRNA treatment results in sustained inhibition of mutant K6a mRNA in patient-derived keratinocyte cultures. These methods allow noninvasive sampling and monitoring of gene expression from patient-collected shavings and may be useful in evaluating the effectiveness of RNAi-based therapeutics, including inhibitors that specifically target single-nucleotide mutations.

Molecular characterization and assessment of therapeutic outcomes for inherited cutaneous disorders requires faithful preclinical models. In this study we report the establishment of two different skin-humanized pachyonychia congenita (PC) model systems, based on permanent engraftment of bioengineered skin equivalents generated from patient skin cells onto immunodeficient mice. Using keratinocytes and fibroblasts isolated from unaffected skin biopsies of two PC patients carrying the p.Asn171Lys mutation of the keratin 6a gene (KRT6A), we were able to regenerate PC-derived human skin that appeared phenotypically normal, but developed sustained PC features after the use of an acute hyperproliferative stimulus (i.e., tape stripping). In contrast, the use of keratinocytes from an affected area (i.e., plantar callus) from a different patient carrying the KRT6A mutation p.Asn171Asp led to a full recapitulation of the phenotype that included marked acanthosis and epidermal blistering after minor trauma. The ability to generate large numbers of PC skin-engrafted mice will enable the testing of novel pharmacological or gene-based therapies for this as yet untreatable disease.

Although RNA interference offers therapeutic potential for treating skin disorders, delivery hurdles have hampered clinical translation. We have recently demonstrated that high pressure, resulting from intradermal injection of large liquid volumes, facilitated nucleic acid uptake by keratinocytes in mouse skin. Furthermore, similar intradermal injections of small interfering RNA (siRNA; TD101) into pachyonychia congenita (PC) patient foot lesions resulted in improvement. Unfortunately, the intense pain associated with hypodermic needle administration to PC lesions precludes this as a viable delivery option for this disorder. To investigate siRNA uptake by keratinocytes, an organotypic epidermal model, in which pre-existing endogenous gene or reporter gene expression can be readily monitored, was used to evaluate the effectiveness of “self-delivery” siRNA (i.e., siRNA chemically modified to enhance cellular uptake). In this model system, self-delivery siRNA treatment resulted in reduction of pre-existing fluorescent reporter gene expression under conditions in which unmodified controls had little or no effect. Additionally, treatment of PC epidermal equivalents with self-delivery “TD101” siRNA resulted in marked reduction of mutant keratin 6a mRNA with little or no effect on wild-type expression. These results indicate that chemical modification of siRNA may overcome certain limitations to transdermal delivery (specifically keratinocyte uptake) and may have clinical utility for inhibition of gene expression in the skin.

Nucleic acid-based therapies hold great promise for treatment of skin disorders if delivery challenges can be overcome. To investigate one mechanism of nucleic acid delivery to keratinocytes, a fixed mass of expression plasmid was intradermally injected into mouse footpads in different volumes, and reporter expression was monitored by intravital imaging or skin sectioning. Reporter gene expression increased with higher delivery volumes, suggesting that pressure drives nucleic acid uptake into cells after intradermal injections similar to previously published studies for muscle and liver. For spatiotemporal analysis of reporter gene expression, a dual-axis confocal (DAC) fluorescence microscope was used for intravital imaging following intradermal injections. Individual keratinocytes expressing hMGFP were readily visualized in vivo and initially appeared to preferentially express in the stratum granulosum and subsequently migrate to the stratum corneum over time. Fluorescence microscopy of frozen skin sections confirmed the patterns observed by intravital imaging. Intravital imaging with the DAC microscope is a noninvasive method for probing spatiotemporal control of gene expression and should facilitate development and testing of new nucleic acid delivery technologies.

The rare skin disorder pachyonychia congenita (PC) is an autosomal dominant syndrome that includes a disabling plantar keratoderma for which no satisfactory treatment is currently available. We have completed a phase Ib clinical trial for treatment of PC utilizing the first short-interfering RNA (siRNA)-based therapeutic for skin. This siRNA, called TD101, specifically and potently targets the keratin 6a (K6a) N171K mutant mRNA without affecting wild-type K6a mRNA. The safety and efficacy of TD101 was tested in a single-patient 17-week, prospective, double-blind, split-body, vehicle-controlled, dose-escalation trial. Randomly assigned solutions of TD101 or vehicle control were injected in symmetric plantar calluses on opposite feet. No adverse events occurred during the trial or in the 3-month washout period. Subjective patient assessment and physician clinical efficacy measures revealed regression of callus on the siRNA-treated, but not on the vehicle-treated foot. This trial represents the first time that siRNA has been used in a clinical setting to target a mutant gene or a genetic disorder, and the first use of siRNA in human skin. The callus regression seen on the patient's siRNA-treated foot appears sufficiently promising to warrant additional studies of siRNA in this and other dominant-negative skin diseases.

RNA interference offers enormous potential to develop therapeutic agents for a variety of diseases. To assess the stability of siRNAs under conditions relevant to clinical use with particular emphasis on topical delivery considerations, a study of three different unmodified siRNAs was performed. The results indicate that neither repeated freeze/thaw cycles, extended incubations (over 1 year at 21 degrees C), nor shorter incubations at high temperatures (up to 95 degrees C) have any effect on siRNA integrity as measured by nondenaturing polyacrylamide gel electrophoresis and functional activity assays. Degradation was also not observed following exposure to hair or skin at 37 degrees C. However, incubation in fetal bovine or human sera at 37 degrees C led to degradation and loss of activity. Therefore, siRNA in the bloodstream is likely inactivated, thereby limiting systemic exposure. Interestingly, partial degradation (observed by gel electrophoresis) did not always correlate with loss of activity, suggesting that partially degraded siRNAs retain full functional activity. To demonstrate the functional activity of unmodified siRNA, EGFP-specific inhibitors were injected into footpads and shown to inhibit preexisting EGFP expression in a transgenic reporter mouse model. Taken together, these data indicate that unmodified siRNAs are viable therapeutic candidates.

We have developed a novel class of antisense agents, RNA Lassos, which are capable of binding to and circularizing around complementary target RNAs. The RNA Lasso consists of a fixed sequence derived from the hairpin ribozyme and an antisense segment whose size and sequence can be varied to base pair with accessible sites in the target RNA. The ribozyme catalyzes self-processing of the 5'- and 3'-ends of a transcribed Lasso precursor and ligates the processed ends to produce a circular RNA. The circular and linear forms of the self-processed Lasso coexist in an equilibrium that is dependent on both the Lasso sequence and the solution conditions. Lassos form strong, noncovalent complexes with linear target RNAs and form true topological linkages with circular targets. Lasso complexes with linear RNA targets were detected by denaturing gel electrophoresis and were found to be more stable than ordinary RNA duplexes. We show that expression of a fusion mRNA consisting of a sequence from the murine tumor necrosis factor-alpha (TNF-alpha) gene linked to luciferase reporter can be specifically and efficiently blocked by an anti-TNF Lasso. We also show in cell culture experiments that Lassos directed against Fas pre-mRNA were able to induce a change in alternative splicing patterns.

The field of science and medicine has experienced a flood of data and technology associated with the human genome project. Over 10,000 human diseases have been genetically defined, but little progress has been made with respect to the clinical application of this knowledge. A notable exception to this exists for pachyonychia congenita (PC), a rare, dominant-negative keratin disorder. The establishment of a non-profit organization, PC Project, has led to an unprecedented coalescence of patients, scientists, and physicians with a unified vision of developing novel therapeutics for PC. Utilizing the technological by-products of the human genome project, such as RNA interference (RNAi) and quantitative RT-PCR (qRT-PCR), physicians and scientists have collaborated to create a candidate siRNA therapeutic that selectively inhibits a mutant allele of KRT6A, the most commonly affected PC keratin. In vitro investigation of this siRNA demonstrates potent inhibition of the mutant allele and reversal of the cellular aggregation phenotype. In parallel, an allele-specific quantitative real-time RT-PCR assay has been developed and validated on patient callus samples in preparation for clinical trials. If clinical efficacy is ultimately demonstrated, this "first-in-skin" siRNA may herald a paradigm shift in the treatment of dominant-negative genetic disorders.

RNA interference offers the potential of a novel therapeutic approach for treating skin disorders. To this end, we investigated delivery of nucleic acids, including a plasmid expressing the reporter gene luciferase, to mouse skin by intradermal injection into footpads using in vivo bioluminescence imaging over multiple time points. In order to evaluate the ability of RNA interference to inhibit skin gene expression, reporter gene constructs were co-injected with specific or non-specific siRNAs and the in vivo effects measured. Our results revealed that specific unmodified and modified siRNAs (but not nonspecific matched controls) strongly inhibit reporter gene expression in mice. These results indicate that small interfering RNA, delivered locally as RNA directly or expressed from viral or non-viral vectors, may be effective agents for treating skin disorders.

In vertebrates, mRNAs containing a 5'-terminal oligopyrimidine (TOP) motif are coordinately post-transcriptionally regulated. Binding of specific proteins to this element has been proposed to downregulate expression of TOP mRNAs at the level of translational initiation. We previously reported that rapamycin induces binding activity to the TOP element of ribosomal protein (r-protein) L32 mRNA. In this study, we adapt DEAE-cellulose/oligo dT-cellulose tandem column chromatography to purify TOP element-binding proteins from bovine submaxillary lymph nodes (SLN). We also show by northwestern blot analysis that two proteins of molecular weight 47kDa (47BP) and 43kDa (43BP) specifically bind to a (32)P-labeled riboprobe containing TOP regulatory element of the r-protein L32. Microsequencing of the purified 47BP revealed an internal sequence of 15 amino acids identical to the consensus sequence of the 2x RBD-Gly family. Western blot analysis of the cytoplasm fractions using an AUF1 antibody revealed that these two proteins are p45 AUF1 and p42 AUF1. Increases of the four isoforms of AUF1 protein were observed in 100,000g supernatant fractions of rapamycin-administered rat SLN. Furthermore, decreases of p45 AUF1 and p42 and/or p40 AUF1 were observed in the polysomal fractions of BJAB cells in which translation of TOP mRNAs was selectively suppressed by rapamycin treatment. Taken together, these results suggest that AUF1 is a TOP mRNA-binding protein that may participate in the translational suppression of TOP mRNAs resulting from rapamycin treatment.

Hepatitis C virus (HCV) is a leading cause of liver cirrhosis and hepatocellular carcinoma worldwide. Currently available treatment options are of limited efficacy, and there is an urgent need for development of alternative therapies. RNA interference (RNAi) is a natural mechanism by which small interfering RNA (siRNA) or short hairpin RNA (shRNA) can mediate degradation of a target RNA molecule in a sequence-specific manner. In this study, we screened in vitro-transcribed 25-bp shRNAs targeting the internal ribosome entry site (IRES) of HCV for the ability to inhibit IRES-driven gene expression in cultured cells. We identified a 44-nt region at the 3! -end of the IRES within which all shRNAs efficiently inhibited expression of an IRES-linked reporter gene. Subsequent scans within this region with 19-bp shRNAs identified even more potent molecules, providing effective inhibition at concentrations of 0.1 nM. Experiments varying features of the shRNA design showed that, for 25-bp shRNAs, neither the size of the loop (4‐10 nt) nor the sequence or pairing status of the ends affects activity, whereas in the case of 19-bp shRNAs, larger loops and the presence of a 3! -UU overhang increase efficacy. A comparison of shRNAs and siRNAs targeting the same sequence revealed that shRNAs were of comparable or greater potency than the corresponding siRNAs. AntiHCV activity was confirmed with HCV subgenomic replicons in a human hepatocyte line. The results indicate that shRNAs, which can be prepared by either transcription or chemical synthesis, may be effective agents for the control of HCV.

Extracellular vesicles (EVs), specifically exosomes and microvesicles (MVs), are presumed to play key roles in cell-cell communication via transfer of biomolecules between cells. The biogenesis of these two types of EVs differs as they originate from either the endosomal (exosomes) or plasma (MVs) membranes. To elucidate the primary means through which EVs mediate intercellular communication, we characterized their ability to encapsulate and deliver different types of macromolecules from transiently transfected cells. Both EV types encapsulated reporter proteins and mRNA but only MVs transferred the reporter function to recipient cells. De novo reporter protein expression in recipient cells resulted only from plasmid DNA (pDNA) after delivery via MVs. Reporter mRNA was delivered to recipient cells by both EV types, but was rapidly degraded without being translated. MVs also mediated delivery of functional pDNA encoding Cre recombinase in vivo to tissues in transgenic Cre-lox reporter mice. Within the parameters of this study, MVs delivered functional pDNA, but not RNA, whereas exosomes from the same source did not deliver functional nucleic acids. These results have significant implications for understanding the role of EVs in cellular communication and for development of EVs as delivery tools. Moreover, studies using EVs from transiently transfected cells may be confounded by a predominance of pDNA transfer.

Treatment and prevention of hepatitis C virus (HCV) infections remain a major challenge for controlling this worldwide health problem; existing therapies are only partially effective and no vaccine is currently available. RNA interference offers the potential of a novel therapeutic approach for treating HCV infections. Toward this end, we evaluated small hairpin interfering RNAs (shRNAs) targeting the conserved internal ribosome entry site (IRES) element of the HCV genome for their ability to control gene expression in human cells and animals. We used a reporter gene plasmid in which firefly luciferase (fLuc) expression is dependent on the HCV IRES. Direct delivery of HCV IRES shRNAs efficiently blocked HCV IRES-mediated fLuc expression in transfected human 293FT cells as well as in a mouse model in which nucleic acids were delivered to liver cells by hydrodynamic transfection via the tail vein. These results indicate that shRNAs, delivered as RNA or expressed from viral or nonviral vectors, may be effective agents for the control of HCV and related viruses.

TOP mRNAs (contain a 5' terminal oligopyrimidine tract) are differentially translated in rapamycin-treated human B lymphocytes. Following rapamycin treatment, ribosomal protein (rp) and translation elongation factor TOP mRNAs were translationally repressed, whereas hnRNP A1 TOP mRNA was not. Poly(A)-binding protein (Pabp1) TOP mRNA was translationally repressed under all conditions tested. To investigate the mechanism involved, chimeric mRNAs containing the hnRNP A1 5' untranslated region (UTR) linked to the human growth hormone (hGH) reporter were analyzed. Wild-type hnRNP A1 construct mRNA behaved similarly to endogenous hnRNP A1, whereas a single mutation (guanosine to cytidine) within the TOP element resulted in increased translational regulation. These results suggest that TOP mRNA translation can be modulated and that all TOP mRNAs are not translated with equal efficiency.

A main challenge in educating undergraduate students is to introduce them to the Internet and to teach them how to effectively use it in research. To this end, an Internet assignment was developed that introduces students to websites related to biomedical research at the beginning of a biochemistry/molecular biology laboratory course. The basic sites introduced cover many subjects, include searching for specific DNA sequences, restriction enzyme mapping, RNA folding, analyzing three-dimensional protein images, and literature searches. These newly learned Internet skills are incorporated into other aspects of the laboratory course. In the example illustrated here, students sequence DNA inserts from randomly chosen bacterial colonies prepared from a human cDNA plasmid library. The obtained DNA sequence is used to search on-line data bases introduced in the initial Internet assignment to determine whether the cDNAs have already been identified. The sequencing “wet-lab” module, coupled with the Internet assignment, gives students experience in four areas. 1) purifying plasmid DNA, 2) performing restriction endonuclease digests on the plasmid DNA, 3) sequencing double-stranded DNA, and 4) comparison of obtained sequence data to known DNA sequences in the human genome data base in a way that simulates a research experience.

Protection (O5‘) of 2‘,3‘-anhydroadenosine with tert-butyldiphenylsilyl chloride and epoxide opening with dimethylboron bromide gave the 3‘-bromo-3‘-deoxy xylo isomer which was treated with benzylisocyanate to give the 2‘-O-(N-benzylcarbamoyl) derivative. Ring closure gave the oxazolidinone, and successive deprotection concluded an efficient route to 3‘-amino-3‘-deoxyadenosine. Analogous treatment of the antibiotic tubercidin {7-deazaadenosine; 4-amino-7-(β-d-ribofuranosyl)pyrrolo[2,3-d]pyrimidine} gave 3‘-amino-3‘-deoxytubercidin. Trifluoroacetylation of the 3‘-amino function, elaboration of the heterocyclic amino group into a (1,2,4-triazol-4-yl) ring with N,N‘-bis[(dimethylamino)methylene]hydrazine, and nucleophilic aromatic substitution with dimethylamine gave puromycin aminonucleoside [9-(3-amino-3-deoxy-β-d-ribofuranosyl)-6-(dimethylamino)purine] and its 7-deaza analogue. Aminoacylation [BOC-(4-methoxy-l-phenylalanine)] and deprotection gave puromycin and 7-deazapuromycin. Most reactions gave high y...

Mammalian tRNA 3′ processing endoribonuclease (3′ tRNase) can remove a 3′ trailer from various precursor (pre)-tRNAs. We investigated what effect the autoantigen La has on 3′ processing, since the La protein is known to bind to a 3′-terminal uridine tract of pre-tRNAs. We tested sixteen different pre-tRNA Arg substrates containing various 3′ trailers with or without a 5′ leader sequence for in vitro processing by pig 3′ tRNase, and for gel-retardation in the presence or absence of human La protein. The R-TUUU series consists of four pre-tRNAs containing 6, 8, 11 and 15 nt 3′ trailers ending with UUU and no 5′ leader, while the R-TAGC series consists of the same four pre-tRNAs as R-TUUU except that the terminal sequence is AGC. The R-6LTUUU and R-6LTAGC series are derived from R-TUUU and R-TAGC, respectively, by adding a 6 nt 5′ leader. La differentially inhibited their processing and bound to the pre-tRNAs; the 50 % inhibitory concentrations for the R-TUUU, R-TAGC, R-6LTUUU, and R-6LTAGC series were 82 to >850, >850, 2 to 292 and 573 to 785 nM, respectively, and the dissociation constants were 10 to 840, >850, 3 to 203 and 155 to 520 nM, respectively. These results indicate that both the terminal sequence UUU and the 5′ leader contribute to more severe inhibition of 3′ processing via tighter interaction with La. With respect to the R-TUUU and R-6LTUUU series, on the whole, the La inhibition was enhanced as the 3′ trailer lengths decreased. Taken together, our results suggest that the La protein sterically hinders 3′ tRNase from binding a pre-tRNA molecule probably near the cleavage site.

Human translation elongation factor 1A (EF1A) is a member of a large class of mRNAs, including ribosomal proteins and other translation elongation factors, which are coordinately translationally regulated under various conditions. Each of these mRNAs contains a terminal oligopyrimidine tract (TOP) that is required for translational control. A human growth hormone (hGH) expression construct containing the promoter region and 5' untranslated region (UTR) of EF1A linked to the hGH coding region (EF1A/hGH) was translationally repressed following rapamycin treatment in similar fashion to endogenous EF1A in human B lymphocytes. Mutation of two nucleotides in the TOP motif abolished the translational regulation. Gel mobility shift assays showed that both La protein from human B lymphocyte cytoplasmic extracts as well as purified recombinant La protein specifically bind to an in vitro-synthesized RNA containing the 5' UTR of EF1A mRNA. Moreover, extracts prepared from rapamycin-treated cells showed increased binding activity to the EF1A 5' UTR RNA, which correlates with TOP mRNA translational repression. In an in vitro translation system, recombinant La dramatically decreased the expression of EF1A/hGH construct mRNA, but not mRNAs lacking an intact TOP element. These results indicate that TOP mRNA translation may be modulated through La binding to the TOP element.

Human MnSOD localizes to the mitochondria and plays a key protective role by detoxifying oxygen free radicals. The MnSOD mRNA 3' UTR contains a 280-bp region (Alu-like element or Alu-E) that shows high homology to human Alu and 7SL sequences. MnSOD 3' UTR probes hybridize to a specific cytoplasmic RNA species of approximately 300 nucleotides. This antisense RNA is most likely 7SL RNA based on its size, ubiquitousness, high levels, and lack of inducibility. Hybridization of this small RNA to the MnSOD 3' UTR may modulate posttranscriptional MnSOD gene expression. This regulation could occur by several means including inhibition of translation and mRNA destabilization. Regulation at the level of translational initiation does not seem to occur as MnSOD mRNA containing the Alu-E is efficiently bound by ribosomes. To test the role of the MnSOD 3' UTR, and in particular the Alu-E in gene expression, luciferase reporter gene constructs were made containing various regions of the MnSOD 3' UTR including the Alu-E. These constructs were transfected into human A549 lung carcinoma cells and luciferase activity was measured. Reporter constructs containing the MnSOD 3' UTR and the Alu-E repress luciferase activity. Taken together, these results suggest that naturally occurring antisense RNA may bind MnSOD mRNA and repress its expression. These results also suggest that other mRNAs containing Alu elements may be similarly repressed.

The 2009 Annual Meeting of the International Pachyonychia Congenita Consortium (IPCC)* centered on the need to develop patient-friendly tech-nologies to effectively and efficiently deliver nucleic acids to skin. The IPCC is a group of physicians and scientists who have agreed to work together to develop therapeutics for the rare skin disorder pachyonychia congenita (PC) (a list of IPCC members can be found at http://www.pachyonychia.org). Each year’s IPCC meeting is devoted to the most pressing issues related to devel-oping PC therapeutics and to identify-ing future directions toward achieving realistic goals. The consortium fully recognizes and expects that research success in this realm will be of imme-diate benefit not only to patients with PC but also to those suffering from other skin disorders.The 2009 meeting addressed the dif-ficulty of delivering nucleic acids to skin. The impetus for this topic was the recent phase Ib pachyonychia congenita clinical trial using a mutation-specific small interfering RNA (siRNA), TD101. The side-by-side, dose-escalation toxicity trial of intralesional injections of this mutation-specific siRNA exhib-ited no toxicity at the higher doses, and a clear clinical response was observed in the siRNA-treated site, but not in the site injected with vehicle alone (Leachman

Mutations in the type I keratin 16 (Krt16) and its partner type II keratin 6 (Krt6a, Krt6b) cause pachyonychia congenita (PC), a disorder typified by dystrophic nails, painful hyperkeratotic calluses in glabrous skin, and lesions involving other epithelial appendages. The pathophysiology of these symptoms and its relationship to settings in which Krt16 and Krt6 are induced in response to epidermal barrier stress are poorly understood. We report that hyperkeratotic calluses arising in the glabrous skin of individuals with PC and Krt16 null mice share a gene expression signature enriched in genes involved in inflammation and innate immunity, in particular damage-associated molecular patterns. Transcriptional hyper-activation of damage-associated molecular pattern genes occurs following de novo chemical or mechanical irritation to ear skin and in spontaneously arising skin lesions in Krt16 null mice. Genome-wide expression analysis of normal mouse tail skin and benign proliferative lesions reveals a tight, context-dependent coregulation of Krt16 and Krt6 with genes involved in skin barrier maintenance and innate immunity. Our results uncover a role for Krt16 in regulating epithelial inflammation that is relevant to genodermatoses, psoriasis, and cancer and suggest a avenue for the therapeutic management of PC and related disorders.

Despite the development of potent siRNAs that effectively target genes responsible for skin disorders, translation to the clinic has been hampered by inefficient delivery through the stratum corneum barrier and into the live cells of the epidermis. Although hypodermic needles can be used to transport siRNA through the stratum corneum, this approach is limited by pain caused by the injection and the small volume of tissue that can be accessed by each injection. The use of microneedle arrays is a less painful method for siRNA delivery, but restricted payload capacity limits this approach to highly potent molecules. To address these challenges, a commercially available motorized microneedle array skin delivery device was evaluated. This device combines the positive elements of both hypodermic needles and microneedle array technologies with little or no pain to the patient. Application of fluorescently tagged self-delivery (sd)-siRNA to both human and murine skin resulted in distribution throughout the treated skin. In addition, efficient silencing (78% average reduction) of reporter gene expression was achieved in a transgenic fluorescent reporter mouse skin model. These results indicate that this device effectively delivers functional sd-siRNA with an efficiency that predicts successful clinical translation.Molecular Therapy-Nucleic Acids (2013) 2, e129; doi:10.1038/mtna.2013.56; published online 22 October 2013.

The structure of m7GpppN (where N is any nucleotide), termed cap, is present at the 5' end of all eukaryotic cellular mRNAs (except organellar). The eukaryotic initiation factor 4E (eIF-4E) binds to the cap and facilitates the formation of translation initiation complexes. eIF-4E is implicated in control of cell growth, as its overexpression causes malignant transformation of rodent cells and deregulates HeLa cell growth. It was suggested that overexpression of eIF-4E results in the enhanced translation of poorly translated mRNAs that encode growth-promoting proteins. Indeed, enhanced expression of several proteins, including cyclin D1 and ornithine decarboxylase (ODC), was documented in eIF-4E-overexpressing NTH 3T3 cells. However, the mechanism underlying this increase has not been elucidated. Here, we studied the mode by which eIF-4E increases the expression of cyclin D1 and ODC. We show that the increase in the amount of cyclin D1 and ODC is directly proportional to the degree of eIF-4E overexpression. Two mechanisms, which are not mutually exclusive, are responsible for the increase. In eIF-4E-overexpressing cells the rate of translation initiation of ODC mRNA was increased inasmuch as the mRNA sedimented with heavier polysomes. For cyclin D1 mRNA, translation initiation was not increased, but rather its amount in the cytoplasm increased, without a significant increase in total mRNA. Whereas, in the parental NIH 3T3 cell line, a large proportion of the cyclin D1 mRNA was confined to the nucleus, in eIF-4E-overexpressing cells the vast majority of the mRNA was present in the cytoplasm. These results indicate that eIF-4E affects directly or indirectly mRNA nucleocytoplasmic transport, in addition to its role in translation initiation.

The polyanionic nature of oligonucleotides and their enzymatic degradation present challenges for the use of siRNA in research and therapy; among the most notable of these is clinically relevant delivery into cells. To address this problem, we designed and synthesized the first members of a new class of guanidinium-rich amphipathic oligocarbonates that noncovalently complex, deliver, and release siRNA in cells, resulting in robust knockdown of target protein synthesis in vitro as determined using a dual-reporter system. The organocatalytic oligomerization used to synthesize these co-oligomers is step-economical and broadly tunable, affording an exceptionally quick strategy to explore chemical space for optimal siRNA delivery in varied applications. The speed and versatility of this approach and the biodegradability of the designed agents make this an attractive strategy for biological tool development, imaging, diagnostics, and therapeutic applications.

The accessibility of skin makes it an ideal target organ for nucleic acid-based therapeutics; however, effective patient-friendly delivery remains a major obstacle to clinical utility. A variety of limited and inefficient methods of delivering nucleic acids to keratinocytes have been demonstrated; further advances will require well-characterized reagents, rapid noninvasive assays of delivery, and well-developed skin model systems. Using intravital fluorescence and bioluminescence imaging and a standard set of reporter plasmids we demonstrate transfection of cells in mouse and human xenograft skin using intradermal injection and two microneedle array delivery systems. Reporter gene expression could be detected in individual keratinocytes, in real-time, in both mouse skin as well as human skin xenografts. These studies revealed that non-invasive intravital imaging can be used as a guide for developing gene delivery tools, establishing a benchmark for comparative testing of nucleic acid skin delivery technologies.

A key challenge in developing RNAi-based therapeutics is efficient delivery of functional short interfering RNA (siRNA) to target cells. To address this need, we have used a supercritical CO2 process to incorporate siRNA in biodegradable polymer nanoparticles (NPs) for in vivo sustained release. By this means we have obtained complete encapsulation of the siRNA with minimal initial burst effect from the surface of the NPs. The slow release of a fluorescently labeled siRNA mimic (siGLO Red) was observed for up to 80 days in vivo after intradermal injection into mouse footpads. In vivo gene silencing experiments were also performed, showing reduction of GFP signal in the epidermis of a reporter transgenic mouse model, which demonstrates that the siRNA retained activity following release from the polymer NPs. 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4261-4266, 2010

Transgenic reporter mice and advances in imag- ing instrumentation are enabling real-time visualization of cellular mechanisms in living subjects and accelerating the development of novel therapies. Innovative confocal microscope designs are improving their utility for micro- scopic imaging of fluorescent reporters in living animals. We develop dual-axis confocal DAC microscopes for such in vivo studies and create mouse models where fluo- rescent proteins are expressed in the skin for the purpose of advancing skin therapeutics and transdermal delivery tools. Three-dimensional image volumes, through the dif- ferent skin compartments of the epidermis and dermis, can be acquired in several seconds with the DAC microscope in living mice, and are comparable to histologic analyses of reporter protein expression patterns in skin sections. In- travital imaging with the DAC microscope further enables visualization of green fluorescent protein GFP reporter gene expression in the skin over time, and quantification of transdermal delivery of small interfering RNA siRNA and therapeutic efficacy. Visualization of transdermal de- livery of nucleic acids will play an important role in the development of innovative strategies for treating skin pathologies. © 2010 Society of Photo-Optical Instrumentation Engineers.

The mRNA encoding ribosomal protein L32 redistributes from untranslated subribosomal particles into polysomes after mitogenic activation of quiescent T-lymphocytes and fibroblasts. To identify the regions of the L32 mRNA which are important in regulating its cytoplasmic location we constructed a plasmid containing the murine L32 cDNA under the control of the Rous sarcoma virus (RSV) long terminal repeat promoter and introduced this construct into murine 3T3 fibroblasts. The mRNA transcribed from the RSV-L32 construct redistributed from subribosomal particles into polysomes in response to mitogenic activation in a manner similar to endogenous L32 mRNA. A conserved polypyrimidine region present at the 5' terminus of all ribosomal protein mRNAs is required for translational regulation of L32 mRNA since deletion of this sequence resulted in a mRNA that was not sequestered in subribosomal particles in quiescent cells. A radioactive RNA probe containing the first 34 nucleotides of the L32 5'-untranslated region, including the polypyrimidine region, specifically interacted with a protein of about 56 kDa. This protein did not bind detectably to RNA probes lacking the polypyrimidine sequence. Binding activity was similar in protein extracts made from resting and activated cells, suggesting that binding of the 56-kDa protein as measured in this assay is not regulated. This protein is a member of what may be an emerging family of polyribopyrimidine-binding proteins with diverse biochemical functions.

Many pharmaceuticals are formulated as powders to aid drug delivery. A major problem is how to produce powders having high purity, controlled morphology, and retained bioactivity. We demonstrate the use of supercritical carbon dioxide as an antisolvent for meeting this need for two model drug systems, quercetin, a sparingly soluble antioxidant, and short interfering RNA (siRNA), which can silence genes. In both cases we achieve retention of bioactivity as well as a narrow particle size distribution in which the particles are free of impurities.

Background The macrolide sirolimus (rapamycin) selectively blocks translation of mRNAs containing a terminal 5′ oligopyrimidine (TOP) tract by altering the activity of mammalian target of rapamycin (mTOR) and inhibiting downstream mTOR pathway components involved in TOP mRNA translation. The skin disorder pachyonychia congenita (PC) is caused by mutations in the inducible keratins (K) including K6a, K6b, K16 and K17. Published sequence data suggest the 5′ untranslated regions of K6a and K6b mRNAs contain 5′ TOP motifs and therefore may be sensitive to rapamycin treatment. Objective Determine if mTOR inhibitors (rapamycin, temsirolimus or everolimus) are viable drug candidates for treatment of PC and other disorders caused by inappropriate expression of K6a and K6b. Methods 5′ RACE analysis was used to map the transcriptional start sites for K5, K6a, K6b, K14, K16 and K17. The sensitivity of these keratins to mTOR inhibitors was determined by Western and qPCR analysis following treatment of a human HaCaT keratinocyte cell line with rapamycin, temsirolimus or everolimus. A small off-label study was undertaken using orally administered rapamycin in three PC patients and the effects were monitored by clinical examination, photography, a validated Dermatology Life Quality Index (DLQI) and a pain and activity diary. Results Sequence comparison and 5′ RACE analysis of the 5′ untranslated regions of K6a and K6b revealed putative TOP regulatory elements. Treatment of a human HaCaT keratinocyte cell line with mTOR inhibitors (rapamycin, temsirolimus or everolimus) resulted in selective K6a repression. Furthermore, treatment of this HaCaT cell line with siRNAs targeting components of the mTOR pathway altered the levels of K6a expression. To test the ability of rapamycin to ameliorate PC symptoms, an off-label study was conducted. PC patient clinical responses to oral rapamycin showed a therapeutic response in callus character as well as subjective improvement. Of particular note, rapamycin greatly reduced the presence of painful cutaneous thromboses after reaching therapeutic serum levels. The well-known rapamycin side effects led to the early withdrawal of all of the patients from the study. Conclusion Rapamycin selectively blocks K6a expression in human keratinocytes. The improvement of symptoms in PC patients following rapamycin treatment suggests rapamycin (or rapamycin analogs) may be a therapeutic option, particularly if topical formulations can be developed that avoid the side effects associated with systemic administration.

We demonstrate microelectromechanical systems (MEMS) based near infrared fluorescence dual-axes confocal (DAC) microscopes in both a 10-mm microscope and a 5-mm endoscope for three-dimensional (3-D) cellular imaging of both ex vivo and in vivo samples.

We demonstrate MEMS based near infrared fluorescence dual-axes confocal (DAC) imaging in a 10-mm-diameter microscope for three-dimensional (3-D) imaging of in vivo human skin. The probe is used to reveal mosaicing two-dimensional (2-D) en face sub-surface histology at depths of up to 250 µm. The probe has a maximum field of view (FOV) of 800×450 µm2 and a maximum acquisition rate of 10 frames/second. The transverse and axial resolutions are 5 µm and 7 µm, respectively.

In this paper, a miniaturized intravital dual-axes confocal (DAC) microscope for investigating gene transfer in skin in vivo was reported. In vivo 3-D imaging not only validates what can be observed in ex vivo tissue sections, but gives spatial and temporal information in a living specimen. This opens up new opportunities in advancing disease and treatment research in the skin.