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Development of imaging methods that can detect target molecules will be of great significance for non-invasive molecular diagnosis. Vascular endothelial growth factor receptor-2 (VEGFR-2) is a broadly expressed target, and VEGFR-2-specific agents have been used in biological therapy. In this study, amine-reactive coupling was used to label the polypeptide VEGF125–136 with a Gd(DOTA) complex to create a magnetic resonance contrast agent, VEGF125–136-Gd, which binds to VEGFR-2. Using T1-weighted magnetic resonance imaging, we explored the tumor cell-targeting ability of VEGF125–136-Gd and its enhancement of T1-weighted image intensity using human hepatoma (HepG2) cells and found that the signal-to-noise ratio (SNR) increased commensurately with the concentration of VEGF125–136-Gd. At a concentration of 2 mM, the SNR produced by VEGF125–136-Gd was 5.4-fold higher than that produced by a Gd-labelled non-targeting polypeptide (NTPP-Gd) control. We also evaluated the tumor-targeting efficiency of VEGF125–136-Gd in nude mice injected with human hepatoma (HepG2) cells. Preliminary in vivo imaging of VEGFR-2 in tumor tissue revealed a targeting peak 60 min post administration of VEGF125–136-Gd, the intensity of which was 23% higher than the SNR of NTPP-Gd at the same time point. Our findings may help lay the foundation for clinical applications of VEGF125–136-Gd in targeted imaging.

A method to calibrate the errors of polarization information measured by division-of-focal-plane polarimeters is demonstrated. The principle of this method is explained, and its feasibility is verified by theoretical simulation and experiment. The simulation and experimental results show that this method can obviously improve the measuring precision of polarization information, and compared with other approaches, the proposed method just uses normal light sources, but can achieve comparable performance.

This paper introduces the working principle of the balanced heterodyne detection system, establishes the corresponding mathematical model, deduces the signal to noise ratio (SNR) formula of the balanced heterodyne detection. By comparing balance heterodyne detection with general coherent detection with MATLAB numerical simulation, the superiority of balance heterodyne detection system is proved theoretically. Finally, the simulation models of ordinary heterodyne detection, balance detection and double balance detection system are built by OptiSystem. The simulation results are consistent with the conclusions derived from the mathematical analysis, which provides a new method for the research of weak laser detection technology.

During the process of transplant operation, pathogens can inevitably come in contact with the implants to cause bacterial infections. Biofilms can then form on the implants, which can enhance the chance of inducing peri-implantitis to result in the failure of implantation. Grafting of anti-biofouling polymer brushes on the implants is a promising method to prevent the above issues. However, degrafting problems of polymer brushes might inhibit durable applications. Herein, we present the fabrication of poly(3-sulfopropyl methacrylate potassium) (PSPMAK) brushes on silicon substrates through multiple single bonds, abbreviated as (M-PSPMAK). These brushes display an enhanced stability, and can remain attached in aqueosus solutions for at least 32 days with less than 10% chain degrafting. The brush-coated surfaces exhibit excellent anti-biofouling behavior against bacteria, while mammalian cells can attach on the surface freely to promote implant interaction with healthy tissues. The stable brushes can also effectively inhibit the formation of a bacterial biofilm. As a proof of principle, we mimicked the implantation process by implanting M-PSPMAK brushes coated silicon in rats. The animal experiments indicate that the brush displays a good anti-biofouling behavior by resisting bacterial attachment. The above results indicate that M-PSPMAK brushes with enhanced stability have great potential to be applied as long-term anti-biofouling coating on artificial implants to reduce the chance of bacterial infection in clinic.

To achieve rapid and sensitive detection of the toxicity of pollutants in the aquatic environment, a photosynthetic inhibition method with microalgae as the test organism and photosynthetic fluorescence parameters as the test endpoint was proposed. In this study, eight environmental pollutants were selected to act on the tested organism, Chlorella pyrenoidosa, including herbicides (diuron, atrazine), fungicides (fuberidazole), organic chemical raw materials (phenanthrene, phenol, p-benzoquinone), disinfectants (trichloroacetonitrile uric acid), and disinfection by-products (trichloroacetonitrile). The results showed that, in addition to specific PSII inhibitors (diuretic and atrazine), other types of pollutants could also quickly affect the photosynthetic system. The photosynthetic fluorescence parameters (Fv/Fm, Yield, α, and rP) could be used to detect the effects of pollutants on the photosynthetic system. Although the decay rate of the photosynthetic fluorescence parameters corresponding to the different pollutants was different, 1 h could be used as an appropriate toxicity exposure time. Moreover, the lowest respondent concentrations of photosynthetic fluorescence parameters to diuron, atrazine, fuberidazole, phenanthrene, P-benzoquinone, phenol, trichloroacetonitrile uric acid, and trichloroacetonitrile were 2 μg·L−1, 5 μg·L−1, 0.05 mg·L−1, 2 μg·L−1, 1.0 mg·L−1, 0.4 g·L−1, 0.1 mg·L−1, and 2.0 mg·L−1, respectively. Finally, diuron, atrazine, fuberidazole, and phenanthrene were selected for a comparison of their photosynthetic inhibition and growth inhibition. The results suggested that photosynthetic inhibition could overcome the time dependence of growth inhibition and shorten the toxic exposure time from more than 24 h to less than 1 h, or even a few minutes, while, the sensitivity of the toxicity test was not weakened. This study indicates that the photosynthetic inhibition method could be used for rapid detection of the toxicity of water pollutants and that algae fluorescence provides convenient access to toxicity data.

Summary: CBX4, a component of polycomb repressive complex 1 (PRC1), plays important roles in the maintenance of cell identity and organ development through gene silencing. However, whether CBX4 regulates human stem cell homeostasis remains unclear. Here, we demonstrate that CBX4 counteracts human mesenchymal stem cell (hMSC) aging via the maintenance of nucleolar homeostasis. CBX4 protein is downregulated in aged hMSCs, whereas CBX4 knockout in hMSCs results in destabilized nucleolar heterochromatin, enhanced ribosome biogenesis, increased protein translation, and accelerated cellular senescence. CBX4 maintains nucleolar homeostasis by recruiting nucleolar protein fibrillarin (FBL) and heterochromatin protein KRAB-associated protein 1 (KAP1) at nucleolar rDNA, limiting the excessive expression of rRNAs. Overexpression of CBX4 alleviates physiological hMSC aging and attenuates the development of osteoarthritis in mice. Altogether, our findings reveal a critical role of CBX4 in counteracting cellular senescence by maintaining nucleolar homeostasis, providing a potential therapeutic target for aging-associated disorders. : Ren et al. identify a geroprotective role for CBX4 in human mesenchymal stem cells (hMSCs) by maintaining nucleolar homeostasis. Overexpression of CBX4 alleviates hMSC aging and attenuates the development of osteoarthritis, highlighting a potential avenue for the use of CBX4 gene therapy vector in treating aging and aging-related disorders. Keywords: CBX4, stem cell, aging, nucleolus, rDNA, epigenetics, heterochromatin, osteoarthritis, CRISPR/Cas9, gene editing

In this paper, a low loss jammed-array wideband sawtooth (JAWS) filter is built based on a finite reflection virtually imaged array (FRVIA) which has a lower reflectivity of the exit surface compared to a virtually imaged phased array (VIPA). This filter can be used as an edge filter to interrogate the fiber Bragg grating (FBG) sensors. A fast FBG sensing system is set up to detect the strain wave of iron pipe to demonstrate the use of this interrogator. The result shows that the JAWS based interrogation system has advantages of high speed, low loss and high sensitivity.

A fiber optic temperature sensor consisting of two cascaded high birefringence fiber loop mirrors (Hi-Bi FLMs) was proposed and experimentally demonstrated to enhance the temperature sensitivity and resolution by Vernier effect. The FSRs for the two Hi-Bi FLMs are designed to be slightly different to generate the Vernier effect. The working principle for the proposed sensor is analogous to Vernier-scale, one Hi-Bi FLM acts as a reference, while the other is for temperature sensing. The temperature sensitivity and resolution for the cascaded configuration are much higher than those for single Hi-Bi FLM due to the Vernier effect. A Gauss fitting algorithm is introduced to fit the Vernier spectral envelope to accurately trace the wavelength shift of the envelope peak. Experimental result shows that the temperature sensitivity and resolution can be improved from − 2.24 nm/°C and ± 0.0223 °C (single Hi-Bi FLM) to − 23.68 nm/°C and ± 0.0021 °C (cascaded configuration), respectively. The enhancement factors for temperature sensitivity and resolution are both 10.6, which are in good agreement with the theoretical prediction (10.7). The proposed sensor with high sensitivity, accuracy, easy fabrication and low cost is highly desirable for some applications that needs precise temperature control, such as micro-nano satellites, lasers, some chemical reaction process and enzyme reaction process.

A technique to selectively excite spin-polarized alkali atoms in one of the two ground-state hyperfine levels is demonstrated, which can separately create the transverse spin component of spin-polarized alkali atoms in either ground-state hyperfine level. The principle of this technique is analyzed, and the experimental results are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this technique. This technique can be used to accurately measure spin relaxation and polarization of alkali atoms in either ground-state hyperfine level. An example of its applications to measure the transverse relaxation time is presented.

Determining the residual field in a magnetic shield is essential in quantum measurement. However, it faces some problems which limit the measuring accuracy. In order to overcome the main problems for the measuring method based on magnetic resonance, a method which detects the electron paramagnetic resonance frequency of 133Cs atoms is reported. By using a rotating exciting magnetic field and choosing appropriate frequency of probe light, the influences of the Bloch-Siegert effect on the measurement of the residual field is eliminated, and by extracting the sums of the residual field and the fictitious field caused by light shifts under different pump light powers and using a second-degree polynomial fitting, the influences of light shifts on the measurement of the residual field is eliminated, thus the residual field is obtained accurately. The test results demonstrate that a high measuring accuracy of 0.01 nT can be achieved for this method.

When the influence of hyperfine structure is ignored for atomic magnetometers, it will lead to considerable measuring errors in some cases. Considering the Cs hyperfine structure, an analytical form of magnetic resonance spectrum of the exciting-field frequency response is obtained through theoretical derivation, which is verified by the experiment. Based on the results of the experimental scheme, the optimal frequency and intensity of pump light for a Cs atomic magnetometer with well-resolved magnetic resonance spectrum are found. Additional applications in minimizing the measuring error of atomic magnetometers and the study of optical pumping are explored.

A highly sensitive strain and temperature sensor which is formed by concatenating a fiber Bragg grating (FBG) with a section of PANDA polarization-maintaining fiber (PMF) in a fiber loop mirror (FLM) has been proposed and experimentally demonstrated to perform temperature and strain measurement. The sensing principle of high birefringence fiber loop mirror (HiBi-FLM) and FBG has been analyzed with formula derivation. Due to the different temperature and strain sensitivities of HiBi-FLM resonant dip and FBG resonant peak, the changes in applied strain and ambient temperature can be simultaneously determined by measuring the two resonance wavelengths shifts. High temperature sensitivity of −1.93 nm/℃ and strain sensitivity of 37.5 pm/μe have been achieved respectively over the range of 20∼55 ℃ and 0∼789.6 μe. The discrimination errors for temperature and strain are measured to be ± 0.5 ℃ and ± 18 μe, respectively. The proposed sensor enjoys simple structure, good linearity, high sensitivity and low cost, and thus shows a good application prospects in various fiber-optic sensing applications.

Optically pumped rubidium atomic magnetometer with elliptically polarized light is demonstrated theoretically and experimentally. Compared with the conventional optical absorption detection mode, the sensitivity of atomic magnetometer for this detection mode can be improved by an order of magnitude under our experimental condition. Some parameters that influence the performance of this magnetometer is studied, which are the form of elliptically polarized light, the amplitude of exciting magnetic field, and the laser intensity. The sensitivity of 2.5 pT/√Hz is obtained when these parameters are optimized.

Infections strongly reduce the success rate of implant-related medical procedures. The incorporation of anti-bacterial implant coatings can reduce the chance of infection. However, most of these coatings do not repel bacteria, such that dead bacteria stay on the surface and the performance of these coatings degrades. Ideally, implant coatings should repel bacteria and inhibit bacterial growth in the event of attachment. Unfortunately, the preparation of such coatings often involve complex and expensive synthesis steps, or rely on antibiotics. In this article, we present a simple, inexpensive and robust technique to prepare implant coatings without the use of antibiotics. Our coatings have both anti-fouling and anti-bacterial properties, such that bacteria do not stick to the implant surface and are killed when they come into contact. The coating is composed of poly(3-sulfopropyl methacrylate potassium salt) (Cu@PSPMAK) polymer brushes doped with copper ions (Cu2+). The Cu2+ in the Cu@PSPMAK coating enables an excellent antibacterial efficiency against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), while the PSPMAK polymer brushes in the coating effectively repel the (dead) bacteria. We show using both in vitro and in vivo tests that the Cu@PSPMAK coating is indeed very effective in avoiding implant-related infections. Moreover, the tests show that the Cu@PSPMAK coating is also biocompatible and accepted within the body. All this makes the Cu@PSPMAK coating an ideal solution for combatting bacterial infections at implants.

We propose and experimentally demonstrate a highly sensitive temperature sensor based on cascaded high birefringence fiber loop mirrors (HiBi-FLMs) with the Vernier effect. The two HiBi-FLMs have almost the same free spectrum range (FSR), which can be regarded as two scales of different periods of an optical Vernier-scale, and act as the fixed part and the sliding part, respectively. A Gauss fitting algorithm is introduced to fit the Vernier spectrum envelope to accurately trace the spectral shift of the envelope. The temperature sensitivity and temperature resolution of the cascaded configuration are much larger than those of the individual HiBi-FLMs due to the Vernier effect. The experimental result shows that the temperature sensitivity of the proposed sensor can be improved from − 1.723 n m / ∘ C (single HiBi-FLM) to − 43 n m / ∘ C (cascaded configuration) by employing the Vernier effect, and the temperature resolution is enhanced from ± 0.029 ∘ C to ± 0.001162 ∘ C . The amplification factors for temperature sensitivity and temperature resolution are both 24.96, which shows good agreement with the theoretical predictions. The proposed sensor with huge temperature sensitivity, high resolution, and simple configuration may be a promising candidate for some applications that need precise temperature control.

We present an all-fiber sensor for strain and temperature discrimination by inserting three sections of high birefringence fibers into a Sagnac loop. The principle for strain and temperature discrimination is based on monitoring the wavelength shifts of two different resonant dips that show different sensitivities to temperature and strain. The sensitivities for strain and temperature are measured to be − 0.93 n m / ∘ C and 21 pm/µɛ with discriminative errors of ± 0.3 ∘ C and ± 12 µ ε . The proposed sensor with high sensitivity, simple configuration, and low cost may be a promising candidate for various strain and temperature-sensing applications.

Loss of organelle homeostasis is a hallmark of aging. However, it remains elusive how this occurs at gene expression level. Here, we report that human mesenchymal stem cell (hMSC) aging is associated with dysfunction of double-membrane organelles and downregulation of transcription factor ATF6. CRISPR/Cas9-mediated inactivation of ATF6 in hMSCs, not in human embryonic stem cells and human adipocytes, results in premature cellular aging, characteristic of loss of endomembrane homeostasis. Transcriptomic analyses uncover cell type-specific constitutive and stress-induced ATF6-regulated genes implicated in various layers of organelles’ homeostasis regulation. FOS was characterized as a constitutive ATF6 responsive gene, downregulation of which contributes to hMSC aging. Our study unravels the first ATF6-regulated gene expression network related to homeostatic regulation of membrane organelles, and provides novel mechanistic insights into aging-associated attrition of human stem cells.

Heterochromatin in aging stem cells Analysis of human aging syndromes, such as Werner syndrome (WS), may lead to greater understanding of both premature and normal aging. Zhang et al. generated isogenic WS-specific human embryonic stem cell lines (see the Perspective by Brunauer and Kennedy). WS-mesenchymal stem cells displayed features characteristic of premature aging, including heterochromatin disorganization. WRN protein thus functions in the maintenance of heterochromatin, and heterochromatin alterations may represent a driving force of human aging. Science , this issue p. 1160 ; see also p. 1093

For realizing optimal performance, knowing the photon absorption cross-section of alkali atoms is significant in a wide range of fields, such as atomic clock, atomic magnetometer and atomic spin gyroscope. By analyzing the pressure broadening and shift, natural broadening and Doppler broadening of the absorption line of 87 Rb D1 line, the numerical simulation of photon absorption cross-section of 87 Rb D1 line is conducted. Based on the results of numerical simulation, natural broadening is found to be much smaller than pressure broadening and Doppler broadening in general. The pressure broadening becomes the dominant factor of broadening for high pressure of buffer and quenching gases, while the Doppler broadening is dominant for low pressure of buffer and quenching gases. The results of numerical simulation demonstrate that, with the increasing broadening of absorption line, the number of peaks of the photon absorption cross-section decreases from four to one gradually, and the amplitudes of these peaks decline in the meantime.

We studied the effects of pump intensity, probe intensity, and pulse amplitude on the transverse relaxation time. Experimental results show paraffin coating offer narrower optical linewidth and larger optical rotation signal than buffer gas.

A practical method to determine the emission frequency of a distributed feedback diode laser at the D1 line of 133Cs is reported. By fitting the extracted dips of the saturated absorption spectrum using linear or quadratic function, this method can realize the measurement of the emission frequency with low cost and simple structure. The test results show that this method can achieve an appreciable measurement range and a high measuring precision of approximately 10 MHz.A practical method to determine the emission frequency of a distributed feedback diode laser at the D1 line of 133Cs is reported. By fitting the extracted dips of the saturated absorption spectrum using linear or quadratic function, this method can realize the measurement of the emission frequency with low cost and simple structure. The test results show that this method can achieve an appreciable measurement range and a high measuring precision of approximately 10 MHz.

In the past few years, progress being made in stem cell studies has incontestably led to the hope of developing cell replacement based therapy for diseases deficient in effective treatment by conventional ways. The induced pluripotent stem cells (iPSCs) are of great interest of cell therapy research because of their unrestricted self-renewal and differentiation potentials. Proof of principle studies have successfully demonstrated that iPSCs technology would substantially benefit clinical studies in various areas, including neurological disorders, hematologic diseases, cardiac diseases, liver diseases and etc. On top of this, latest advances of gene editing technologies have vigorously endorsed the possibility of obtaining disease-free autologous cells from patient specific iPSCs. Here in this review, we summarize current progress of stem cell therapy research with special enthusiasm in iPSCs studies. In addition, we compare current gene editing technologies and discuss their potential implications in clinic application in the future.

A global aging population, normally accompanied by a high incidence of aging-associated diseases, has prompted a renewed interest in basic research on human aging. Although encouraging progress has been achieved using animal models, the underlying fundamental mechanisms of aging remain largely unknown. Here, we review the human induced pluripotent stem cell (hiPSC)-based models of aging and aging-related diseases. These models seek to advance our knowledge of aging molecular mechanisms and help to develop strategies for treating aging-associated human diseases.

Nuclear lamins, the major components of the nuclear lamina, participate in maintaining the nuclear structure and are involved in essential cellular processes, including DNA replication and chromatin organization. To date, more than 15 human diseases classified as laminopathies have been linked to mutations in components of the nuclear lamina. With the development of induced pluripotent stem cell (iPSC) and targeted gene editing technologies, novel disease models of laminopathies have been generated. These models will improve our understanding of the pathological mechanism of laminopathies and may eventually lead to the discovery of new therapeutic approaches for the treatment of these devastating diseases.

Human induced pluripotent stem cells (iPSCs) hold unprecedented potential to model human development and genetic disorders due to their capability to self-renew and differentiate into any somatic cell type. In the year of 2011, a number of iPSC disease models have been successfully developed for studying the mechanism of human diseases as well as establishing platforms for drug screening and testing (Batista et al., 2011; Brennand et al., 2011; Devine et al., 2011; Itzhaki et al., 2011; Koch et al., 2011; Liu et al., 2011a; Mazzulli et al., 2011; Nguyen et al., 2011; Pasca et al., 2011; Quarto et al., 2011; Tiscornia et al., 2011; Wu and Hochedlinger, 2011; Yazawa et al., 2011; Zhang et al., 2011; Zhu et al., 2011). One key hypothesis of current iPSC disease models is based on the presumption that wild type and diseased iPSCs are equal to their embryonic stem cell (ESC) counterparts. However, this hypothesis seems to be challenged by several recent findings on the striking differences between ESCs and iPSCs. At the genomic level, the reprogramming process tends to cause the accumulation of DNA mutations as well as other chromosomal abnormalities related to cancer pathways (Panopoulos et al., 2011). Whereas there is no relevant in vivo data indicating that these mutations are indeed linked to tumorigenesis, the genetic aberrances accumulated during reprogramming probably interfere with the cellular parameters in either iPSCs or their differentiated derivatives. If specific diseases, especially those associated with genomic instability, facilitate the accumulation of more genetic mutations during reprogramming, this could result in wrong explanation of the phenotypes of iPSC disease models. In fact, the evaluation on how aspects of specific diseases affect reprogramming-associated mutations has not been reported. Additionally, at the epigenomic level, the residual epigenetic memories of iPSCs from their original cellular environment likely represent another barrier to being a true phenocopy of their ESC counterparts. In support of this, mouse iPSCs, but not ESCs, show immune rejection upon transplantation (Zhao et al., 2011), suggesting that subtle epigenetic differences might cause substantially different cell identities. To date, it is not clear whether disease-associated epigenetic memories exist in patient-specific iPSCs. Only a few groups examined the successful resetting of abnormal epigenetic marks during reprogramming, such as histone and DNA methylation, in their iPSC disease models (Marchetto et al., 2010; Liu et al., 2011a). At the differentiation level, a number of reports have shown that iPSCs behave differently from their ESC counterparts (Buchholz et al., 2009; Bock et al., 2011; Kim et al., 2011), although researchers still don’t know how this difference affects recapitulation of disease phenotypes in vitro. It should also be noted that certain diseased somatic cellular environments might contribute to the defective reprogramming with a higher possibility. For example, cellular defects in Fanconi anemia patient fibroblasts resulted in a complete blockage of iPSC generation (Raya et al., 2009). Hence, to avoid misinterpretation of results, it seems essential to first evaluate whether generated patient iPSCs are completely reset to a patient ESC-like status. Along this line, thorough examination of various cellular parameters in patient-specific iPSCs could be a critical step before employment of any iPSC disease model in mechanistic studies or drug testing. As complementary approaches, the relevant assays with overexpression of a mutant (e.g. for dominant mutation) or knock-down of an endogenous protein (e.g. for recessive mutation) in disease-related cell types should be included to verify the specific aspects of disease phenotypes. Furthermore, the lack of appropriate control iPSC lines constructs another important experimental limitation for the use of patient-derived iPSCs. In fact, the “wild type” or “healthy” iPSC lines currently used as controls are derived from “phenotypically normal” populations, which nevertheless carry various genetic and epigenetic polymorphisms. The major concern with respect to these epigenetic and genetic variations is that they may cause inconsistent phenotypic

An edge filter is a potential technology in the fiber Bragg grating interrogation that has the advantages of fast response speed and suitability for dynamic measurement. To build a low loss, wideband jammed-array wideband sawtooth (JAWS) filter, a finite reflection virtually imaged array (FRVIA) is proposed and demonstrated. FRVIA is different from the virtually imaged phased array in that it has a low reflective front end. This change will lead to many differences in the device’s performance in output optical intensity distribution, spectral resolution, output aperture, and tolerance of the manufacture errors. A low loss, wideband JAWS filter based on an FRVIA can provide an edge filter for each channel, respectively.

The influence of optical pumping on the transverse spin relaxation of 133 Cs atoms in different ground-state hyperfine levels is investigated. Transverse relaxation times for 133 Cs atoms in the two ground-state hyperfine levels are detected separately under different intensities and frequencies of pump light, and a statistical model is adopted to analyze the experimental results. Theory and experiment show that optical pumping changes the populations of the two ground-state hyperfine levels, thereby influencing the transverse spin relaxation due to spin-exchange collisions. As a result, an unusual phenomenon that the transverse relaxation time for 133 Cs atoms in the upper ground-state hyperfine level increases with the pump-light intensity is observed.

Werner syndrome (WS) is a premature aging disorder caused by WRN protein deficiency. Here, we report on the generation of a human WS model in human embryonic stem cells (ESCs). Differentiation of WRN-null ESCs to mesenchymal stem cells (MSCs) recapitulates features of premature cellular aging, a global loss of H3K9me3, and changes in heterochromatin architecture. We show that WRN associates with heterochromatin proteins SUV39H1 and HP1α and nuclear lamina-heterochromatin anchoring protein LAP2β. Targeted knock-in of catalytically inactive SUV39H1 in wild-type MSCs recapitulates accelerated cellular senescence, resembling WRN-deficient MSCs. Moreover, decrease in WRN and heterochromatin marks are detected in MSCs from older individuals. Our observations uncover a role for WRN in maintaining heterochromatin stability and highlight heterochromatin disorganization as a potential determinant of human aging.