Search

• Hedgehog responsive cells [Gli1(+) cells] exist in perineurium and endoneurium. • Gli1(+) cells in endoneurium were classified as blood vessel associated or non-associated. • Gli1(+) cells accumulate into the injury site along with endothelial cells after injury. • Loss of Hh signal activity in Gli1(+)cells cause disorganized vascularization. • Loss of Hh signal activity in Gli1(+)cells results in failure of axonal regeneration. Hh signaling has been shown to be activated in intact and injured peripheral nerve. However, the role of Hh signaling in peripheral nerve is not fully understood. In the present study, we observed that Hh signaling responsive cells [Gli1(+) cells] in both the perineurium and endoneurium. In the endoneurium, Gli1(+) cells were classified as blood vessel associated or non-associated. After injury, Gli1(+) cells around blood vessels mainly proliferated to then accumulate into the injury site along with endothelial cells. Hh signaling activity was retained in Gli1(+) cells during nerve regeneration. To understand the role of Hedgehog signaling in Gli1(+) cells during nerve regeneration, we examined mice with Gli1(+) cells-specific inactivation of Hh signaling (Smo cKO). After injury, Smo cKO mice showed significantly reduced numbers of accumulated Gli1(+) cells along with disorganized vascularization at an early stage of nerve regeneration, which subsequently led to an abnormal extension of the axon. Thus, Hh signaling in Gli1(+) cells appears to be involved in nerve regeneration through controlling new blood vessel formation at an early stage. [ABSTRACT FROM AUTHOR]

• Repressor form of Gli3 suppress Hh signaling in Schwann cells of intact peripheral nerve. • After nerve injury, repressor form of Gli3 in Schwann cells is reduced, which leads to Hh signaling activity. • Gli3 mutation facilitates up-regulation of Shh signaling in injured nerve and subsequent peripheral nerve regeneration. Hedgehog (Hh) signaling has been shown to be involved in regulating both intact and injured peripheral nerves. Therefore, it is critical to understand how Hh signaling is regulated in the peripheral nerve. One of the transcription factors of the Hh signaling pathway, Gli3, functions as both a repressor and an activator of Hh signaling activity. However, it remains unclear whether Gli3 is involved in controlling the intact and/or injured peripheral nerves. We found that Gli3 act as a repressor in the Schwann cells (SCs) of intact sciatic nerves. Although Dhh and Ptch1 expression were present, Hh signaling was not activated in these SCs. Moreover, heterozygous Gli3 mutation (Gli3−/+) induced ectopic Hh signaling activity in SCs. Hh signaling was thus suppressed by Gli3 in the SCs of intact sciatic nerves. Minor morphological changes were observed in the intact nerves from Gli3−/+ mice. Gli3 expression was significantly decreased following injury and ligand expression switched from Dhh to Shh, which activated Hh signaling in SCs from wild-type mice. Changes of these ligands was found to be important for nerve regeneration in which the downregulation of Gli3 was also involved. In fact, Gli3−/+ mice exhibited accelerated ligand switching and subsequent nerve regeneration. Both suppression of Hh signaling with Gli3 in the intact nerves and activation of Hh signaling without Gli3 in the injured nerve were observed in the SCs in an autocrine manner. Thus, Gli3 is a key factor in the control of intact peripheral nerve homeostasis and nerve regeneration. [ABSTRACT FROM AUTHOR]

Developmentally inclined hedgehog (HH) signaling pathway and pluripotency inducing transcription factor SOX2 have been known to work syngerstically during cellular reprogramming events to facilitate efficient differentiation. Hence, it is not surprising that both the factors are actively involved in arbitrating malignant growth, including prostate cancer progression. Here, we have described in details the potential mechanisms by which SOX2 effects neoplastic characteristics in prostate cancer and investigated the consequences of simultaneous down-regulation of SOX2 and HH pathway in androgen-independent human prostate cancer cells. Expression of SOX2 has been determined by qRT-PCR, western blot, immunohistochemistry and immunocytochemistry analyses; its functional role determined by gene knockdown using RNAi and over-expression via chemical activation in HaCaT, DU145 and PC-3 cells. Changes in level of cell proliferation, migration and apoptosis profiles were measured by MTT, FACS, chromatin condensation and scratch assays respectively. SOX2 was expressed in all the three cell lines and its inhibition reduced cell proliferation and induced apoptosis. Most importantly, when both SOX2 and HH pathway were targeted simultaneously, cell proliferation was greatly reduced, apoptotic cell population increased drastically and migration potential was reduced. Moreover, gene expression of EMT markers such as E-cadherin and apoptosis related Bcl-2 and Bax was also investigated wherein decrease in E-cadherin and Bcl-2 levels and increase in Bax expression further substantiating our claim. These findings could provide the basis for a novel therapeutic strategy targeting both the effector i.e. SOX2 and perpetuator i.e. HH pathway of aggressive tumorigenic properties in androgen independent prostate cancer. [ABSTRACT FROM AUTHOR]

Oxysterols, oxidized derivatives of cholesterol, are biologically active molecules. Specific oxysterols have potent osteogenic properties that act on osteoprogenitor cells. However, the molecular mechanisms underlying these osteoinductive effects on embryonic stem cells (ESCs) are unknown. This study investigated the effect of an oxysterol combination of 22(S)-hydroxycholesterol and 20(S)-hydroxycholesterol (SS) on osteogenic differentiation of ESCs and the alterations to mitochondrial activity during differentiation. Osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity, matrix mineralization, mRNA expression of osteogenic factors, runt-related transcription factor 2, osterix, and osteocalcin, and protein levels of collagen type IA (COLIA) and osteopontin (OPN). Treatment of cells with SS increased osteoinductive activity compared to the control group. Intracellular reactive oxygen species production, intracellular ATP content, mitochondrial membrane potential, mitochondrial mass, mitochondrial DNA copy number, and mRNA expression of peroxisome proliferator-activated receptor-γ coactivators 1α and β, transcription factors involved in mitochondrial biogenesis, were significantly increased during osteogenesis, indicating upregulation of mitochondrial activity. Oxysterol combinations also increased protein levels of mitochondrial respiratory complexes I–V. We also found that SS treatment increased hedgehog signaling target genes, Smo and Gli1 expression. Inhibition of Hh signaling by cyclopamine suppressed mitochondrial biogenesis and ESC osteogenesis. Subsequently, oxysterol-induced Wnt/β-catenin pathways were inhibited by repression of Hh signaling and mitochondrial biogenesis. Transfection of β-catenin specific siRNA decreased the protein levels of COLIA and OPN, as well as ALP activity. Collectively, these data suggest that lipid-based oxysterols enhance differentiation of ESCs toward the osteogenic lineage by regulating mitochondrial activity, canonical Hh/Gli, and Wnt/β-catenin signaling. [ABSTRACT FROM AUTHOR]

Abstract: Cdon and Boc, and their Drosophila homologues Ihog and Boi, are evolutionary conserved transmembrane glycoproteins belonging to a subgroup of the Immunoglobulin superfamily of cell adhesion molecules (CAMs). Initially isolated in vertebrates as CAMs that link cadherin function with MAPK signaling in myoblast differentiation, they have thereafter been shown to act as essential receptors for the Hedgehog (Hh) family of secreted proteins. They associate with both ligand and other Hh receptor components, including Ptch and Gas1, thus forming homo- and heteromeric complexes. In Drosophila, they are also involved in ligand processing and release from Hh producing cells. Cdon/Boc and Ihog/Boi can substitute one another and play redundant functions is some contexts. In addition, Boc, but not Cdon, mediates axon guidance information provided by Hh in specific neuronal populations, whereas mutations in the CDON cause holoprosencephaly, a human congenital anomaly defined by forebrain midline defects prominently associated with diminished Hh pathway activity. [Copyright &y& Elsevier]

Chromatin remodelers often show broad expression patterns in multiple cell types yet can elicit cell-specific effects in development and diseases. Arid1a binds DNA and regulates gene expression during tissue development and homeostasis. However, it is unclear how Arid1a achieves its functional specificity in regulating progenitor cells. Using the tooth root as a model, we show that loss of Arid1a impairs the differentiation-associated cell cycle arrest of tooth root progenitors through Hedgehog (Hh) signaling regulation, leading to shortened roots. Our data suggest that Plagl1, as a co-factor, endows Arid1a with its cell-type/spatial functional specificity. Furthermore, we show that loss of Arid1a leads to increased expression of Arid1b, which is also indispensable for odontoblast differentiation but is not involved in regulation of Hh signaling. This study expands our knowledge of the intricate interactions among chromatin remodelers, transcription factors, and signaling molecules during progenitor cell fate determination and lineage commitment. [Display omitted] • Arid1a promotes the proliferation-differentiation transition of root progenitors • Hh signaling participates in Arid1a's regulation of tooth root progenitor cell fate • Plagl1 endows Arid1a with its cell-type/spatial functional specificity • Arid1b is crucial for odontoblast differentiation but not involved in Hh signaling Du et al. show that Arid1a promotes the transition of root progenitors from proliferation to differentiation through Hh signaling regulation. Plagl1 endows Arid1a with cell-type/spatial functional specificity. Loss of Arid1a leads to increase of Arid1b, which is also indispensable for odontoblast differentiation but is not involved in Hh signaling. [ABSTRACT FROM AUTHOR]

Bone is a dynamic organ that is continuously modified during development, load-induced adaptation, and fracture repair. Understanding the cellular and molecular mechanisms for natural fracture healing can lead to therapeutics that enhance the quality of newly formed tissue, advance the rate of healing, or replace the need for invasive surgical procedures. Prx1-expressing cells in the periosteum are thought to supply the majority of osteoblasts and chondrocytes in the fracture callus, but the exact mechanisms for this behavior are unknown. The primary cilium is a sensory organelle that is known to mediate several signaling pathways involved in fracture healing and required for Prx1-expressing cells to contribute to juvenile bone development and adult load-induced bone formation. We therefore investigated the role of Prx1-expressing cell primary cilia in fracture repair by developing a mouse model that enabled us to simultaneously track Prx1 lineage cell fate and disrupt Prx1-expressing cell primary cilia in vivo. The cilium KO mice exhibited abnormally large calluses with significantly decreased bone formation and persistent cartilage nodules. Analysis of mRNA expression in the early soft callus revealed downregulation of osteogenesis, Hh signaling, and Wnt signaling, and upregulation of chondrogenesis and angiogenesis. The mutant mice also exhibited decreased Osx and Periostin but increased αSMA and PECAM-1 protein expression in the hard callus. We further used a Gli1LacZ reporter and found that Hh signaling was significantly upregulated in the mutant callus at later stages of healing. Interestingly, altered protein expression and Hh signaling did not correlate with labeled Prx1-lineage cells, suggesting loss of cilia altered Hh signaling non-autonomously. Overall, cilium KO mice demonstrated severely delayed and incomplete fracture healing, and our findings suggest Prx1-expressing cell primary cilia are necessary to tune Hh signaling for proper fracture repair. • Primary cilia are sensory organelles important for bone maintenance and healing. • Fracture healing is severely delayed in mice lacking Prx1-expressing cell primary cilia. • Mutant fracture calluses contain more cartilage and vasculature but less bone. • Primary cilia function is critical for several signaling pathways associated with healing. [ABSTRACT FROM AUTHOR]