Intervertebral disc-intrinsic Hedgehog signaling maintains disc cell phenotypes and prevents disc degeneration through both cell autonomous and non-autonomous mechanisms.

Intervertebral disc degeneration is closely related to abnormal phenotypic changes in disc cells. However, the mechanism by which disc cell phenotypes are maintained remains poorly understood. Here, Hedgehog-responsive cells were found to be specifically localized in the inner annulus fibrosus and cartilaginous endplate of postnatal discs, likely activated by Indian Hedgehog. Global inhibition of Hedgehog signaling using a pharmacological inhibitor or Agc1-CreERT2-mediated deletion of Smo in disc cells of juvenile mice led to spontaneous degenerative changes in annulus fibrosus and cartilaginous endplate accompanied by aberrant disc cell differentiation in adult mice. In contrast, Krt19-CreER-mediated deletion of Smo specifically in nucleus pulposus cells led to healthy discs and normal disc cell phenotypes. Similarly, age-related degeneration of nucleus pulposus was accelerated by genetic inactivation of Hedgehog signaling in all disc cells, but not in nucleus pulposus cells. Furthermore, inactivation of Gli2 in disc cells resulted in partial loss of the vertebral growth plate but otherwise healthy discs, whereas deletion of Gli3 in disc cells largely corrected disc defects caused by Smo ablation in mice. Taken together, our findings not only revealed for the first time a direct role of Hedgehog-Gli3 signaling in maintaining homeostasis and cell phenotypes of annuls fibrosus and cartilaginous endplate, but also identified disc-intrinsic Hedgehog signaling as a novel non-cell-autonomous mechanism to regulate nucleus pulposus cell phenotype and protect mice from age-dependent nucleus pulposus degeneration. Thus, targeting Hedgehog signaling may represent a potential therapeutic strategy for the prevention and treatment of intervertebral disc degeneration.

Scar-related atrial macroreentries: Different arrhymogenic basis generates different reentry type.

BACKGROUND: Catheter ablation is an established therapeutic strategy to treat scar-related macroreentry atrial tachycardia (MAT). However, the scar properties and arrhythmogenicity and the reentry type have not been clearly defined. METHODS AND RESULTS: A total of 122 patients with scar-related MAT were enrolled in this study. The atrial scars were classified into two categories: spontaneous scars (Group A: n = 28) and iatrogenic scars (Group B: n = 94). According to the relationship between scar location and the reentry circuit, MAT was described as scar pro-flutter MAT, scar-dependent MAT, and scar-mediated MAT. The reentry type of MAT was significantly different between Groups A and B: pro-flutter (40.5% vs. 62.0%, p = 0.02), scar-dependent AT (40.5% vs. 13.0%, p < 0.001), and scar-mediated AT (19.0% vs. 25.0%, p = 0.42). After a median follow-up of 25 months, 21 patients with AT recurrence were observed. Compared with the spontaneous group, there was a lower recurrence rate of MAT in the iatrogenic group (28.6% vs. 10.6%, p = 0.03). CONCLUSION: Scar-related MAT has three reentry types, and the proportion of each type varies with the scar properties and its arrhythmogenic basis. Optimization of the ablation strategy based on the scar properties to improve the long-term outcome of catheter ablation of MAT is necessary.

Persistent left superior vena cava isolation in patients with atrial fibrillation: Selective or empirical?

BACKGROUND: Persistent left superior vena cava (PLSVC) is the most prevalent form of thoracic venous abnormality and can serve as a significant arrhythmogenic source in atrial fibrillation (AF). METHODS AND RESULTS: Among the 3950 patients who underwent radiofrequency ablation for AF between September 2014 to April 2020, 17 patients (mean age 59.4 ± 8.0 years, 64.7% male) with PLSVC were identified. Among them, nine patients (52.9%) had a prior history of pulmonary vein isolation (PVI) alone. Eight out of nine patients who experienced AF recurrence underwent PLSVC isolation with or without pulmonary vein (PV) reconnection. For the remaining eight patients (47.1%), PVI plus PLSVC isolation were performed during the index procedure. Ectopy originating from PLSVC was documented in 11 patients (64.7%) and successful PLSVC isolation was achieved in 16 patients (94.1%). After a median follow-up of 28.3 months, freedom from AF/ atrial tachycardia (AT) was observed in 13 patients (76.5%). CONCLUSION: Empirical PLSVC isolation beyond PVI appears to be a feasible and safe strategy to prevent AF recurrence in patients with concomitant PLSVC.

Gaucher disease in a patient with membranoproliferative glomerulonephritis: case report.

BACKGROUND: Gaucher disease (GD) is a rare autosomal recessive inherited, lysosomal storage disoder that involves liver, spleen, lung, bone, bone marrow even central nervous. However, GD associated membranoproliferative glomerulonephritis (MPGN) is seldom reported. CASE PRESENTATION: Here we described a case of 35-year-old man suffering from GD with hepatosplenomegaly, ascites, bone destruction, myelofibrosis and MPGN. Renal biopsy revealed MPGN and Gaucher cells presented in the glomeruli capillaries. ß-glucosidase activity was 1.95nmol/1 h/mg and gene detection demonstrated that one homozygous pathogenic variant Leu483Pro in GBA. He received the treatment of oral prednisone and mycophenolate mofetil and his ascites and renal outcomes had been significantly improved. CONCLUSIONS: Therapy of prednisone and mycophenolate mofetil may be an optional choice for patients with Gaucher disease who have no opportunity to use enzyme treatment.

PP2Acα regulates epidermal cell proliferation via the EGFR/AKT/mTOR pathway in psoriasis-like skin lesions caused by PPP2CA deficiency.

Psoriasis, a common skin disease, endangers human physiological and mental health; however, its pathogenesis remains unclear. Keratinocyte proliferation is a typical pathological characteristic of psoriasis. Serine/threonine protein phosphatase 2A (PP2A) is one of the most important phosphatases for maintaining normal phosphorylation levels in humans. PP2Acα is the alpha subtype of the PP2A C subunit (encoded by PPP2CA), which maintains the catalytic functions of PP2A. Epidermal growth factor receptor (EGFR) is activated by phosphorylation (p-EGFR) to regulate the downstream signalling pathway to promote epidermal cell proliferation. Previous studies have found that PPP2CA induced epidermal hyperplasia, keratinization and other pathological phenomena similar to those in mouse models of psoriasis. The present study showed that PP2Acα negatively regulated EGFR phosphorylation and epidermal cell proliferation, and EGFR inhibitors could alleviate PP2Acα by inhibiting epidermal cell proliferation. This study further examined the effect of mechanisms on epidermal cell proliferation and the downstream signalling pathway of EGFR using molecular technological methods to explore new ideas for treating psoriasis.

Prevalence and Risk Factors for Fall among Rural Elderly: A County-Based Cross-Sectional Survey.

Aim: The aim of the study was to provide evidence for the prevention and reduction of falls in the elderly living in rural areas by analyzing epidemiological data of falls among the rural older people (>65 years old) and identifying the risk and protective factors. Methods: This study analyzed the sociodemographic characteristics, living environment, lifestyle, chronic disease condition, mental health, activities of daily living (ADL), and detailed information of falls of 3752 rural elderly. Rank tests, chi-square tests, and binary logistic regression were used for data analysis. Results: The prevalence of falls was 30.0%, and the 75-84-years age group had the highest fall rate (18.8%). According to the binary logistic regression analysis, six variables, including roughage intake frequency, age, gender, cane use, floor tiles, and IADL, were involved in the fall patterns. Low roughage intake (OR = 2.48, 95% CI 1.24-4.97), female gender (OR = 2.12, 95% CI 1.48-3.05), the use of a cane (OR = 2.11, 95% CI 1.08-4.10), and medium IADL (OR = 2.02, 95% CI 1.89-2.32) were the top four risk factors. Conclusion: The fall in the rural elderly was mainly due to the poor living and working conditions. Routine fall assessment could address several preventable risk factors to reduce the prevalence and mitigate the harm of falls.

Telomerase Reverse Transcriptase and p53 Regulate Mammalian Peripheral Nervous System and CNS Axon Regeneration Downstream of c-Myc.

Although several genes have been identified to promote axon regeneration in the CNS, our understanding of the molecular mechanisms by which mammalian axon regeneration is regulated is still limited and fragmented. Here by using female mouse sensory axon and optic nerve regeneration as model systems, we reveal an unexpected role of telomerase reverse transcriptase (TERT) in regulation of axon regeneration. We also provide evidence that TERT and p53 act downstream of c-Myc to control sensory axon regeneration. More importantly, overexpression of p53 in sensory neurons and retinal ganglion cells is sufficient to promote sensory axon and optic never regeneration, respectively. The study reveals a novel c-Myc-TERT-p53 signaling pathway, expanding horizons for novel approaches promoting CNS axon regeneration.SIGNIFICANCE STATEMENT Despite significant progress during the past decade, our understanding of the molecular mechanisms by which mammalian CNS axon regeneration is regulated is still fragmented. By using sensory axon and optic nerve regeneration as model systems, the study revealed an unexpected role of telomerase reverse transcriptase (TERT) in regulation of axon regeneration. The results also delineated a c-Myc-TERT-p53 pathway in controlling axon growth. Last, our results demonstrated that p53 alone was sufficient to promote sensory axon and optic nerve regeneration in vivo Collectively, the study not only revealed a new mechanisms underlying mammalian axon regeneration, but also expanded the pool of potential targets that can be manipulated to enhance CNS axon regeneration.

Inhibition of PTEN activity promotes IB4-positive sensory neuronal axon growth.

Traumatic nerve injuries have become a common clinical problem, and axon regeneration is a critical process in the successful functional recovery of the injured nervous system. In this study, we found that peripheral axotomy reduces PTEN expression in adult sensory neurons; however, it did not alter the expression level of PTEN in IB4-positive sensory neurons. Additionally, our results indicate that the artificial inhibition of PTEN markedly promotes adult sensory axon regeneration, including IB4-positive neuronal axon growth. Thus, our results provide strong evidence that PTEN is a prominent repressor of adult sensory axon regeneration, especially in IB4-positive neurons.

c-Myc controls the fate of neural progenitor cells during cerebral cortex development.

The anatomical structure of the mammalian cerebral cortex is the essential foundation for its complex neural activity. This structure is developed by proliferation, differentiation, and migration of neural progenitor cells (NPCs), the fate of which is spatially and temporally regulated by the proper gene. This study was used in utero electroporation and found that the well-known oncogene c-Myc mainly promoted NPCs' proliferation and their transformation into intermediate precursor cells. Furthermore, the obtained results also showed that c-Myc blocked the differentiation of NPCs to postmitotic neurons, and the expression of telomere reverse transcriptase was controlled by c-Myc in the neocortex. These findings indicated c-Myc as a key regulator of the fate of NPCs during the development of the cerebral cortex.

Circular RNA expression profiling in the fetal side of placenta from maternal polycystic ovary syndrome and circ_0023942 inhibits the proliferation of human ovarian granulosa cell.

PURPOSE: Circular RNAs (circRNAs) are widely expressed noncoding RNAs which play important roles in various processes. The present study aimed to explore the effect of maternal PCOS on the expression of circRNAs in fetus and assessed the potential role of circRNA in human ovarian granulosa cell proliferation. METHODS: Total RNA was extracted from the fetal side of placental tissues from maternal PCOS (n = 3) and healthy puerpera (n = 3) for circRNA microarray. Real-time reverse transcriptase quantitative PCR (RT-qPCR) was used to validate the microarray data in fetal side of placental tissues from puerpera with (n = 18) and without (n = 30) PCOS. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were applied to predict the functions and pathways of circ_0023942 host genes. The circRNA-miRNA-mRNA network was constructed through bioinformatics prediction. Circ_0023942 overexpression vector was transiently transfected into human ovarian granulosa cell lines KGN and COV434. Cell proliferation was detected by cell counting kit-8. The protein expression level was determined by western blot. RESULTS: Compared with healthy puerpera, 14 circRNAs were significantly upregulated and 101 circRNAs were significantly downregulated in the fetal side of placenta from maternal PCOS according to the microarray data. Six differentially expressed circRNAs were selected for validation by RT-qPCR, and the expression patterns of circ_0023942, circ_0002151, circ_0001274, and circ_0008514 were consistent with the microarray data. Circ_0023942 was chosen for further investigation. GO and KEGG analysis predicted that circ_0023942 participated in the regulation of developmental process and the MAPK signaling pathway. Seven miRNAs were predicted to be the targets of circ_0023942. Overexpression of circ_0023942 inhibited human ovarian granulosa cell proliferation and suppressed the expression of CDK-4. CONCLUSION: Maternal PCOS impairs circ_0023942 expression in fetus. Overexpression of circ_0023942 inhibits human ovarian granulosa cell proliferation possibly via regulating CDK-4.

TGFß1 and HGF regulate CTGF expression in human atrial fibroblasts and are involved in atrial remodelling in patients with rheumatic heart disease.

OBJECTIVE: This study aimed to investigate the effects of transforming growth factor ß1 (TGF ß1) and hepatocyte growth factor (HGF) on the expression of connective tissue growth factor (CTGF) in human atrial fibroblasts, and to explore the relationship of these factors in atrial fibrosis and atrial anatomical remodelling (AAR) of patients with atrial fibrillation (AF). METHODS: Fresh right auricular appendix tissue of 20 patients with rheumatic heart disease undergoing valve replacement surgery was collected during surgeries, 10 patients had sinus rhythm(SR), and 10 patients had chronic atrial fibrillation (CAF). Atrial fibroblasts were then cultured from the tissues with differential attachment technique and treated with either TGFß1 (10 ng/mL) or HGF (100 ng/mL). CTGF mRNA levels were measured by RT-PCR, and CTGF protein content was determined using immunofluorescence and Western blotting assays. RESULTS: CAF group had higher left atrial diameters (LADs) and higher CTGF mRNA expression in atrial fibroblasts compared with SR group. The CTGF protein content in CAF group was higher than that of SR group and positively correlated with LAD and AF duration. After CAF group was treated with TGFß1, CTGF mRNA and protein expression were significantly down-regulated, whereas when treated with HGF, expression was up-regulated compared with SR group. CONCLUSIONS: Increased CTGF expression was associated with enlarged LAD, atrial fibrosis and AAR in patients with AF. TGFß1 and HGF regulate CTGF expression in human atrial fibroblasts with up-regulation of mRNA and down-regulation of protein, therefore, either promote or inhibit atrial fibrosis, which could be related to the incidence and persistence of AF.

Proinflammatory macrophages promote degenerative phenotypes in rat nucleus pulpous cells partly through ERK and JNK signaling.

Intervertebral disc (IVD) degeneration is the major contributor to low back pain, a highly prevalent musculoskeletal problem that represents the leading cause of disability. Proinflammatory M1 macrophages were identified in degenerated IVDs. However, their role in the pathogenesis of IVD degeneration and the underlying mechanism was largely unknown. In this study, we explored the combined effects of molecules secreted by M1 macrophages on nucleus pulposus cells, by treating rat nucleus pulposus cells (rNP) with the conditioned medium collected from M1-polarized RAW264.7 cells (MФCM). We found that MФCM caused molecular changes associated with IVD degeneration, including increased expression of key matrix catabolic genes (Adamts4, Adamts5, Mmp3, and Mmp13), reduced the expression of major matrix-associated anabolic genes ( Sox9, Acan, and Col2a1), and upregulated transcription of inflammation-related genes ( IL-1b, IL-6, Ccl2, and Ccl3), in rNP cells. Moreover, we found that MФCM activated both ERK and JNK pathways in these cells, and that inhibition of JNK pathway attenuated MФCM-induced expression of both catabolic and inflammatory genes, whereas ERK inhibition only suppressed induction of catabolic, but not inflammatory genes. Together, our data demonstrated that proinflammatory macrophages promoted the degenerative phenotypes in rNP cells in part through ERK and JNK signaling, and suggested that inhibition of these pathways may serve as a potential therapeutic approach for the treatment of IVD degeneration.

A dual role of cholesterol in osteogenic differentiation of bone marrow stromal cells.

Osteoblasts, the chief bone-forming cells, are differentiated from mesenchymal stromal/stem cells. Disruption of this differentiation process can cause osteoporosis, a bone disease characterized by low bone mass and deteriorated bone structure. Cholesterol has been implicated in pathogenesis of osteoporosis, and was recently identified as an endogenous activator of Hedgehog (Hh) signaling. However, its pathological and physiological roles in osteoblast differentiation are still poorly understood. Moreover, it is unclear whether these potential roles played by cholesterol are related to its capability to modulate Hh pathway. In this study, we investigated the role of exogenous versus endogenous cholesterol in osteogenesis and Hh pathway activation using ST2 cells, a bone marrow stromal cell line. We found that exogenous cholesterol significantly inhibited alkaline phosphatase (ALP) activity and messenger RNA expression of osteoblast markers genes (Alpl, Sp7, and Ibsp) while modestly activating expression of Gli1 (a readout of Hh signaling) under both basal osteogenic culture condition and Wnt3a treatment. Similarly, exogenous cholesterol suppressed osteogenic response of ST2 cells to sonic Hh (Shh) or purmorphamine (Purmo) treatment, which, however, was accompanied by diminished induction of Gli1, indicating the involvement of a Hh-dependent mechanism. Interestingly, depletion of endogenous cholesterol also reduced Shh-induced ALP activity and Gli1 expression. Likewise, cholesterol depletion inhibited osteogenic response to Purmo, although it did not affect Gli1 induction. Taken together, our findings have demonstrated that cholesterol plays a dual role in osteoblast differentiation likely through both Hh-dependent and -independent mechanisms.

Matrix remodeling associated 7 promotes differentiation of bone marrow mesenchymal stem cells toward osteoblasts.

The matrix remodeling associated 7 (MXRA7) gene had been ill-studied and its biology remained to be discovered. Inspired by our previous findings and public datasets concerning MXRA7, we hypothesized that the MXRA7 gene might be involved in bone marrow mesenchymal stem cells (BMSCs) functions related to bone formation, which was checked by utilizing in vivo or in vitro methodologies. Micro-computed tomography of MXRA7-deficient mice demonstrated retarded osteogenesis, which was reflected by shorter femurs, lower bone mass in both trabecular and cortical bones compared with wild-type (WT) mice. Histology confirmed the osteopenia-like feature including thinner growth plates in MXRA7-deficient femurs. Immunofluorescence revealed less osteoblasts in MXRA7-deficient femurs. Polymerase chain reaction or western blot analysis showed that when WT BMSCs were induced to differentiate toward osteoblasts or adipocytes in culture, MXRA7 messenger RNA or protein levels were significantly increased alongside osteoblasts induction, but decreased upon adipocytes induction. Cultured MXRA7-deficient BMSCs showed decreased osteogenesis upon osteogenic differentiation induction as reflected by decreased calcium deposition or lower expression of genes responsible for osteogenesis. When recombinant MXRA7 proteins were supplemented in a culture of MXRA7-deficient BMSCs, osteogenesis or gene expression was fully restored. Upon osteoblast induction, the level of active ß-catenin or phospho-extracellular signal-regulated kinase in MXRA7-deficient BMSCs was decreased compared with that in WT BMSCs, and these impairments could be rescued by recombinant MXRA7 proteins. In adipogenesis induction settings, the potency of MXRA7-deficient BMSCs to differentiate into adipocytes was increased over the WT ones. In conclusion, this study demonstrated that MXRA7 influences bone formation via regulating the balance between osteogenesis and adipogenesis in BMSCs.

Characterization of Cre recombinase mouse lines enabling cell type-specific targeting of postnatal intervertebral discs.

Cre/loxP technology is an important tool for studying cell type-specific gene functions. Cre recombinase mouse lines, including Agc1-CreERT2 , Col2a1-Cre; Col2a1-CreERT2 , Shh-Cre, Shh-CreERT2 , and Osx-Cre, have been proven to be valuable tools to elucidate the biology of long bones, yet the information for their activity in postnatal intervertebral disc (IVD) tissues was very limited. In this study, we used R26-mTmG fluorescent reporter to systematically analyze cell specificity and targeting efficiency of these six mouse lines in IVD tissues at postnatal growing and adult stages. We found that Agc1-CreERT2 is effective to direct recombination in all components of IVDs, including annulus fibrosus (AF), nucleus pulposus (NP), and cartilaginous endplate (CEP), upon tamoxifen induction at either 2 weeks or 2 months of ages. Moreover, Col2a1-Cre targets most of the cells in IVDs, except for some cells in the outer AF (OAF) and NP. In contrast, the activity of Col2a1-CreERT2 is mainly limited to the IAF of IVD tissues at either stage of tamoxifen injection. Similarly, Shh-Cre directs recombination specifically in all NP cells, whereas Shh-CreERT2 is active only in a few NP cells when tamoxifen is administered at either stage. Finally, Osx-Cre targets cells in the CEP, but not in the NP or AF of IVDs tissues at these two stages. Thus, our data demonstrated that all these Cre lines can direct recombination in IVD tissues at postnatal stages with different cell type specificity and/or targeting efficiency, and can, therefore, serve as valuable tools to dissect cell type-specific gene functions in IVD development and homeostasis.

Regulation of adult mammalian intrinsic axonal regeneration by NF-κB/STAT3 signaling cascade.

The inflammatory response is a critical regulator for the regeneration of axon following nervous system injury. Nuclear factor-kappa B (NF-κB) is characteristically known for its ubiquitous role in the inflammatory response. However, its functional role in adult mammalian axon growth remains elusive. Here, we found that the NF-κB signaling pathway is activated in adult sensory neurons through peripheral axotomy. Furthermore, inhibition of NF-κB in peripheral sensory neurons attenuated their axon growth in vitro and in vivo. Our results also showed that NF-κB modulated axon growth by repressing the phosphorylation of STAT3. Furthermore, activation of STAT3 significantly promoted adult optic nerve regeneration. Taken together, the findings of our study indicated that NF-κB/STAT3 cascade is a critical regulator of intrinsic axon growth capability in the adult nervous system.

Calcium/calmodulin-dependent protein kinase II regulates mammalian axon growth by affecting F-actin length in growth cone.

While axon regeneration is a key determinant of functional recovery of the nervous system after injury, it is often poor in the mature nervous system. Influx of extracellular calcium (Ca2+ ) is one of the first phenomena that occur following axonal injury, and calcium/calmodulin-dependent protein kinase II (CaMKII), a target substrate for calcium ions, regulates the status of cytoskeletal proteins such as F-actin. Herein, we found that peripheral axotomy activates CaMKII in dorsal root ganglion (DRG) sensory neurons, and inhibition of CaMKII impairs axon outgrowth in both the peripheral and central nervous systems (PNS and CNS, respectively). Most importantly, we also found that the activation of CaMKII promotes PNS and CNS axon growth, and regulatory effects of CaMKII on axon growth occur via affecting the length of the F-actin. Thus, we believe our findings provide clear evidence that CaMKII is a critical modulator of mammalian axon regeneration.

FGF signaling in the osteoprogenitor lineage non-autonomously regulates postnatal chondrocyte proliferation and skeletal growth.

Fibroblast growth factor (FGF) signaling is important for skeletal development; however, cell-specific functions, redundancy and feedback mechanisms regulating bone growth are poorly understood. FGF receptors 1 and 2 (Fgfr1 and Fgfr2) are both expressed in the osteoprogenitor lineage. Double conditional knockout mice, in which both receptors were inactivated using an osteoprogenitor-specific Cre driver, appeared normal at birth; however, these mice showed severe postnatal growth defects that include an ∼50% reduction in body weight and bone mass, and impaired longitudinal bone growth. Histological analysis showed reduced cortical and trabecular bone, suggesting cell-autonomous functions of FGF signaling during postnatal bone formation. Surprisingly, the double conditional knockout mice also showed growth plate defects and an arrest in chondrocyte proliferation. We provide genetic evidence of a non-cell-autonomous feedback pathway regulating Fgf9, Fgf18 and Pthlh expression, which led to increased expression and signaling of Fgfr3 in growth plate chondrocytes and suppression of chondrocyte proliferation. These observations show that FGF signaling in the osteoprogenitor lineage is obligately coupled to chondrocyte proliferation and the regulation of longitudinal bone growth.

Cell type-specific effects of Notch signaling activation on intervertebral discs: Implications for intervertebral disc degeneration.

Intervertebral disc (IVD) degeneration is the major cause of back pain. Notch signaling is activated in annulus fibrosus (AF) and nucleus pulposus (NP) tissues of degenerated IVDs, and induced by IL1-ß and TNF-α in NP cells. However, the role of Notch activatin in the pathogenesis of IVD degeneration is largely unknown. In this study, we overexpressed the Notch1 intracellular domain (NICD1) in AF, NP, and chondrogenic ATDC5 cells via adenoviruses. Overexpression of NICD1 activated transcription of Notch signaling target genes in AF, NP, and ATDC5 cells, and caused cell type-specific effects on expression of matrix anabolic and catabolic genes. Activation of Notch signaling promoted expression of matrix catabolic genes and inhibited expression of matrix anabolic genes in both AF and ATDC5 cells, whereas its activation suppressed expression of matrix catabolic genes (including Mmp3, Mmp13, Adamts4, and Adamts5) and attenuated TNF-α and inflammatory macrophage-induced Mmp13 expression in NP cells. Consistently, sustained activation of Notch1 signaling in postnatal IVDs in mice severely disrupted growth plate and endplate cartilage tissues, but did not overly affect NP tissues. Together, these data indicated that activation of Notch signaling exerted differential and cell type-specific effects in intervertebral discs, and specific Notch signaling regulation may be considered during the treatment of IVD degeneration.

Osteocyte-intrinsic mTORC1 signaling restrains trabecular bone accrual in mice.

Mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signaling plays important physiological roles in bone homeostasis by regulating multiple steps of osteoblast differentiation as well as its activity. However, its potential role in osteocytes has not been explored. In this study, we deleted Raptor, a specific and essential component of mTORC1, in osteocytes using Dmp1-Cre. Deletion of Raptor in osteocytes did not affect bone development and growth, but caused compartment-specific effects on bone mass. Osteocyte-specific deletion of Raptor had no obvious effect on cortical bone compartments, but led to increased trabecular bone mass. Mechanistically, Raptor deletion resulted in decreased bone resorption without altering bone formation activity. Thus, our study revealed an unexpected role of osteocyte-intrinsic mTORC1 signaling in limiting trabecular bone mass, suggesting that osteocyte-specific inhibition of mTORC1 may be used as a novel approach to treatment of osteoporosis.