Bone morphogenetic protein-2 and -7 mediate the anabolic function of nucleus pulposus cells with discrete mechanisms.

Bone morphogenetic proteins (BMPs) play roles in promoting cell anabolism, especially in extracellular matrix production. The difference between BMP members in their capacity to modulate intervertebral disc cell activity is yet to be defined. BMP-7/OP-1 has been shown to retard disc degeneration. We compared the activity of BMP-7 with that of BMP-2 on nucleus pulposus (NP) cell phenotype and function, and investigated how they differentially affect the gene expression profiles of signaling cascade components in human NP cells under degenerative states. We found that while both BMP-2 and BMP-7 enhanced matrix production of bovine NP cells, BMP-7 is more potent than BMP-2 at various dosages (50-800 ng/ml). BMP-7 exerted a relatively stronger stimulation on sulfated glycosaminoglycan production and proliferation in human NP cells. Degenerated NP cells showed an overall weaker response to the BMPs than non-degenerated cells, and were more sensitive to BMP-7 than BMP-2 stimulation. Compared to BMP-2, BMP-7 not only induced the gene expression of canonical BMP components, but also evoked changes in MAPKs as well as CREB1 and EP300 gene expression in degenerated NP cells, suggesting potential activation of the cAMP dependent protein kinase related pathways. In contrast to BMP-2, BMP-7 concomitantly inhibited the expression of profibrotic genes. We propose that BMP-2 and BMP-7, and likely other BMPs, may operate multifaceted but discrete molecular machineries that give rise to their different capacity in regulating NP cell phenotype. Further investigations into such differential capacity may possibly derive alternative cues important for IVD repair or engineering.

Lumbar intervertebral disc allograft transplantation: long-term mobility and impact on the adjacent segments.

PURPOSE: Fresh-frozen intervertebral disc (IVD) allograft transplantation has been successfully performed in the human cervical spine. Whether this non-fusion technology could truly decrease adjacent segment disease is still unknown. This study evaluated the long-term mobility of the IVD-transplanted segment and the impact on the adjacent spinal segments in a goat model. METHODS: Twelve goats were used. IVD allograft transplantation was performed at lumbar L4/L5 in 5 goats; the other 7 goats were used as the untreated control (5) and for the supply of allografts (2). Post-operation lateral radiographs of the lumbar spine in the neutral, full-flexion and full-extension positions were taken at 1, 3, 6, 9 and 12 months. Disc height (DH) of the allograft and the adjacent levels was calculated and range of motion (ROM) was measured using the Cobb's method. The anatomy of the adjacent discs was observed histologically. RESULTS: DH of the transplanted segment was decreased significantly after 3 months but no further reduction was recorded until the final follow-up. No obvious alteration was seen in the ROM of the transplanted segment at different time points with the ROM at 12 months being comparable to that of the untreated control. The DH and ROM in the adjacent segments were well maintained during the whole observation period. At post-operative 12 months, the ROM of the adjacent levels was similar to that of the untreated control and the anatomical morphology was well preserved. CONCLUSIONS: Lumbar IVD allograft transplantation in goats could restore the segmental mobility and did not negatively affect the adjacent segments after 12 months.

Concise review: the surface markers and identity of human mesenchymal stem cells.

The concept of mesenchymal stem cells (MSCs) is becoming increasingly obscure due to the recent findings of heterogeneous populations with different levels of stemness within MSCs isolated by traditional plastic adherence. MSCs were originally identified in bone marrow and later detected in many other tissues. Currently, no cloning based on single surface marker is capable of isolating cells that satisfy the minimal criteria of MSCs from various tissue environments. Markers that associate with the stemness of MSCs await to be elucidated. A number of candidate MSC surface markers or markers possibly related to their stemness have been brought forward so far, including Stro-1, SSEA-4, CD271, and CD146, yet there is a large difference in their expression in various sources of MSCs. The exact identity of MSCs in vivo is not yet clear, although reports have suggested they may have a fibroblastic or pericytic origin. In this review, we revisit the reported expression of surface molecules in MSCs from various sources, aiming to assess their potential as MSC markers and define the critical panel for future investigation. We also discuss the relationship of MSCs to fibroblasts and pericytes in an attempt to shed light on their identity in vivo.

Mesenchymal stem cells reduce intervertebral disc fibrosis and facilitate repair.

Intervertebral disc degeneration is associated with back pain and radiculopathy which, being a leading cause of disability, seriously affects the quality of life and presents a hefty burden to society. There is no effective intervention for the disease and the etiology remains unclear. Here, we show that disc degeneration exhibits features of fibrosis in humans and confirmed this in a puncture-induced disc degeneration (PDD) model in rabbit. Implantation of bone marrow-derived mesenchymal stem cells (MSCs) to PDD discs can inhibit fibrosis in the nucleus pulposus with effective preservation of mechanical properties and overall spinal function. We showed that the presence of MSCs can suppress abnormal deposition of collagen I in the nucleus pulposus, modulating profibrotic mediators MMP12 and HSP47, thus reducing collagen aggregation and maintaining proper fibrillar properties and function. As collagen fibrils can regulate progenitor cell activities, our finding provides new insight to the limited self-repair capability of the intervertebral disc and importantly the mechanism by which MSCs may potentiate tissue regeneration through regulating collagen fibrillogenesis in the context of fibrotic diseases.

In search of nucleus pulposus-specific molecular markers.

Intervertebral disc degeneration usually starts from the inner nucleus pulposus (NP). The majority of previous NP-related studies assessed the outcome by the expression of chondrogenic markers since NP cells are chondrocyte like. However, NP cells are unique from chondrocytes and such assessments may be inappropriate. Very recently, several investigators published their findings about the transcriptional differences between NP cells and other related cell types on a genomic scale. In this review we discuss these recent findings and summarize the molecules that may be utilized as NP-specific markers to distinguish normal NP cells from several cell types and as markers that indicate its degeneration. We will revisit markers that distinguish NP cells from the outer surrounding annulus fibrosus (AF) cells and articular chondrocytes so as to facilitate authentic NP cell engineering from stem cells. Our review indicated that N-cadherin and keratin 19 have the potential to serve as common NP markers, as they distinguish healthy NP cells from AF cells, articular cartilage cells and degenerated NP cells.

Correction for concentration overestimation of nucleic acids with phenol.

We report a computational method based on ultraviolet (UV) spectra for correcting the overestimated concentrations of nucleic acid samples contaminated with TRIzol/phenol. The derived correction formulas were validated using RNA solutions, double-stranded DNA solutions, and single-stranded oligonucleotide solutions. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) with SYBR Green was performed to assess the level of TRIzol contamination that can be tolerated for gene expression quantification. After the correction, the accuracy of the RNA concentrations was greatly improved and there was no significant difference in the threshold cycle (Ct) values for GAPDH and ACAN genes in RT-qPCR obtained for RNA contaminated with up to 0.1% TRIzol (phenol level index [PLI]∼5.8-5.9). Similarly, accuracy improvements were also observed for DNA or oligonucleotides contaminated with phenol using different concentration correction formulas. In addition, the Ct values and amplification efficiency of DNA in qPCR were not affected by TRIzol contamination below 1%. This computational method is easy and convenient to use and reduces the concentration overestimations greatly.

SOX9 governs differentiation stage-specific gene expression in growth plate chondrocytes via direct concomitant transactivation and repression.

Cartilage and endochondral bone development require SOX9 activity to regulate chondrogenesis, chondrocyte proliferation, and transition to a non-mitotic hypertrophic state. The restricted and reciprocal expression of the collagen X gene, Col10a1, in hypertrophic chondrocytes and Sox9 in immature chondrocytes epitomise the precise spatiotemporal control of gene expression as chondrocytes progress through phases of differentiation, but how this is achieved is not clear. Here, we have identified a regulatory element upstream of Col10a1 that enhances its expression in hypertrophic chondrocytes in vivo. In immature chondrocytes, where Col10a1 is not expressed, SOX9 interacts with a conserved sequence within this element that is analogous to that within the intronic enhancer of the collagen II gene Col2a1, the known transactivation target of SOX9. By analysing a series of Col10a1 reporter genes in transgenic mice, we show that the SOX9 binding consensus in this element is required to repress expression of the transgene in non-hypertrophic chondrocytes. Forced ectopic Sox9 expression in hypertrophic chondrocytes in vitro and in mice resulted in down-regulation of Col10a1. Mutation of a binding consensus motif for GLI transcription factors, which are the effectors of Indian hedgehog signaling, close to the SOX9 site in the Col10a1 regulatory element, also derepressed transgene expression in non-hypertrophic chondrocytes. GLI2 and GLI3 bound to the Col10a1 regulatory element but not to the enhancer of Col2a1. In addition to Col10a1, paired SOX9-GLI binding motifs are present in the conserved non-coding regions of several genes that are preferentially expressed in hypertrophic chondrocytes and the occurrence of pairing is unlikely to be by chance. We propose a regulatory paradigm whereby direct concomitant positive and negative transcriptional control by SOX9 ensures differentiation phase-specific gene expression in chondrocytes. Discrimination between these opposing modes of transcriptional control by SOX9 may be mediated by cooperation with different partners such as GLI factors.

Progenitor-like cells contributing to cellular heterogeneity in the nucleus pulposus are lost in intervertebral disc degeneration.

The nucleus pulposus (NP) in the intervertebral disc (IVD) arises from embryonic notochord. Loss of notochordal-like cells in humans correlates with onset of IVD degeneration, suggesting that they are critical for healthy NP homeostasis and function. Comparative transcriptomic analyses identified expression of progenitor-associated genes (GREM1, KRT18, and TAGLN) in the young mouse and non-degenerated human NP, with TAGLN expression reducing with aging. Lineage tracing using Tagln-CreERt2 mice identified peripherally located proliferative NP (PeriNP) cells in developing and postnatal NP that provide a continuous supply of cells to the entire NP. PeriNP cells were diminished in aged mice and absent in puncture-induced degenerated discs. Single-cell transcriptomes of postnatal Tagln-CreERt2 IVD cells indicate enrichment for TGF-ß signaling in Tagln descendant NP sub-populations. Notochord-specific removal of TGF-ß/BMP mediator Smad4 results in loss of Tagln+ cells and abnormal NP morphologies. We propose Tagln+ PeriNP cells are potential progenitors crucial for NP homeostasis.

Slow twitch paraspinal muscle dysregulation in adolescent idiopathic scoliosis exhibiting HIF-2α misexpression.

Background: Adolescent idiopathic scoliosis (AIS) refers to a three-dimensional spinal deformity which has a typical onset during adolescence. In most cases, the cause of the deformity cannot be clearly identified. Unbalanced paraspinal muscle activity in AIS patients was reported and hypoxia was implicated to regulate myogenesis. This study aims to investigate the association between myogenesis/muscle toning and HIF-αs activity in the pathogenesis of AIS. Methods: HIF-αs expression was examined by enzyme-linked immunosorbent assay and western blot in paraspinal myoblasts isolated from 18 subjects who underwent deformity correction surgery. QPCR was conducted to measure the gene expression levels of perinatal muscle fiber markers MYH3, MYH8; slow twitch muscle fiber markers MHY7; fast twitch muscle fiber markers MYH4; and myogenic regulatory factors MYF5 and MYOG. Slow and fast twitch muscle fiber composition in concave/convex paraspinal musculature of AIS subjects was evaluated by immunostaining of myosin heavy chain type I (MyHC I) and myosin heavy chain type II (MyHC II). Results: Reduced HIF-2α induction under hypoxia was found in paraspinal myoblast culture of 33% AIS subjects. We detected a suppression of perinatal and slow twitch muscle fiber associated genes, but not fast twitch muscle fiber-associated genes and myogenic regulatory factors in HIF-2α misexpressed AIS myoblasts. Distinct reduction of slow twitch muscle fiber was evidenced in convex paraspinal musculature, suggesting an asymmetric expression of slow twitch muscle fiber in HIF-2α misexpressed AIS patients. Conclusions: This study indicates an association of abnormal HIF-2α expression in paraspinal myoblasts and a disproportionate slow twitch muscle fiber content in the convexity of the curvature in a subset of AIS subjects, suggesting HIF-2α dysregulation as a possible risk factor for AIS. The role of HIF-2α in paraspinal muscle function during spinal growth and its relevance in AIS prognosis warrants further investigation.

Minimizing cryopreservation-induced loss of disc cell activity for storage of whole intervertebral discs.

Severe intervertebral disc (IVD) degeneration often requires disc excision and spinal fusion, which leads to loss of spinal segment mobility. Implantation of an allograft disc or tissue engineered disc construct emerges as an alternative to artificial disc replacement for preserving the motion of the degenerated level. Establishment of a bank of cadaveric or engineered cryopreserved discs enables size matching, and facilitates clinical management. However, there is a lack of understanding of the behaviour of disc cells during cryopreservation, as well as how to maximize their survival, such that disc graft properties can be preserved. Here, we report on the effect of alterations in cooling rates, cryoprotective agents (CPAs), and duration of pre-cryopreservation incubation in CPA on cellular activity in whole porcine lumbar discs. Our results indicated that cooling rates of -0.3 degrees C/min and -0.5 degrees C/min resulted in the least loss of metabolic activity in nucleus pulposus (NP) and annulus fibrosus (AF) respectively, while metabolic activity is best maintained by using a combination of 10% dimethylsulphoxide (DMSO) and 10% propylene-glycol (PG) as CPA. By the use of such parameters, metabolic activity of the NP and the AF cells could be maintained at 70% and 45%, respectively, of that of the fresh tissue. Mechanical testing and histological evaluation showed no significant differences in mechanical properties or alterations in disc structure compared to fresh discs. Despite the limitations of the animal model, our findings provide a framework for establishing an applicable cryopreservation protocol for human disc allografts or tissue-engineered disc constructs.

Injury-induced sequential transformation of notochordal nucleus pulposus to chondrogenic and fibrocartilaginous phenotype in the mouse.

Intervertebral disc degeneration has been widely studied in different animal models. To test the hypothesis that needle puncture could induce progressive biochemical and molecular changes in murine discs, we established a mouse tail model to investigate the pathogenesis and molecular mechanism of puncture-induced disc degeneration. Caudal discs in mouse tails were punctured using a 31G gauge needle at controlled depth under microscopic guidance. The progress of the disc degeneration was evaluated by radiographic analysis of disc height, histological grading and glycosaminoglycan (GAG) quantification pre-operation and 1, 2, 6 and 12 weeks post-puncture. Gene and protein expression of the extracellular matrix (ECM) was analysed by RT-PCR, in situ hybridization and immunohistochemistry. Histological study and disc height analysis revealed progressive degenerative changes in the punctured discs. Compared with the pre-operation control group, total GAG content decreased 40% (p < 0.05) and aggrecan (Acan), decorin (Dcn) and versican (Vcan; Cspg2) expression was down-regulated at 12 weeks post-puncture. A transient increase of Col2a1-expressing cells and elevation of collagen II protein in the nucleus pulposus (NP) was detected. Fibronectin (Fn1) expression was up-regulated 50% and deposition of collagen I in NP was observed at 12 weeks post-puncture. This study is the first to use an injury-induced model to study disc degeneration in mouse. The disc degeneration involves a transient transformation of NP from notochordal to chondrogenic and eventually into fibrocartilaginous phenotype. The degenerative changes have some similarity to human disc degeneration, suggesting that this model may potentially be used in future to study the molecular mechanism and dissect the pathways of disc degeneration.

Mesenchymal stem cells arrest intervertebral disc degeneration through chondrocytic differentiation and stimulation of endogenous cells.

Degenerative disc disease (DDD) is a common disease which affects millions of people. Autograft of the bone marrow derived mesenchymal stem cells (BMSCs) have been shown to have the ability to arrest degeneration in rabbit and canine intervertebral discs. In this study, we have used the mouse model to investigate the mechanism of degeneration arrest. BMSC from Egfp transgenic mice were injected into the degenerated murine intervertebral discs induced by annular puncture. We found that BMSC could arrest the progressive degeneration of the discs with significant regeneration of the nucleus pulposus (NP). In the regeneration, expression of proteoglycan genes were upregulated and extracellular matrix (ECM) progressively accumulated in the NP after BMSC injection. Combined in situ hybridization and immunohistochemistry revealed that BMSC underwent chondrocytic differentiation in the regeneration process. Interestingly, BMSC-induced an increase of endogenous notochordal cells in NP and expression of chondrocytic markers. In this study, we have firstly shown that the BMSC could arrest the degeneration of the murine notochordal NP and contribute to the augmentation of the ECM in the NP by both autonomous differentiation and stimulatory action on endogenous cells.

Transformation of resident notochord-descendent nucleus pulposus cells in mouse injury-induced fibrotic intervertebral discs.

Intervertebral disc degeneration (IDD), a major cause of low back pain, occurs with ageing. The core of the intervertebral disc, the nucleus pulposus (NP), embedded in a proteoglycan-rich and gelatinous matrix, is derived from the embryonic notochord. With IDD, the NP becomes fibrous, containing fewer cells, which are fibroblastic and of unknown origin. Here, we used a lineage tracing strategy to investigate the origin of cells in the NP in injury-induced mouse IDD. We established a Foxa2 notochord-specific enhancer-driven Cre transgenic mouse model (Foxa2mNE-Cre) that acts only in the embryonic to foetal period up to E14.5, to genetically label notochord cells with enhanced green fluorescent protein (EGFP). When this mouse is crossed to one carrying a Cre recombinase reporter, Z/EG, EGFP-labelled NP cells are present even at 2 years of age, consistent with their notochordal origin. We induced tail IDD in Foxa2mNE-Cre; Z/EG mice by annulus puncture and observed the degenerative changes for 12 weeks. Soon after puncture, EGFP-labelled NP cells showed strong Col2a1+ expression unlike uninjured control NP. Later, accompanying fibrotic changes, EGFP-positive NP cells expressed fibroblastic and myofibroblastic markers such as Col1a1, ASMA, FAPA and FSP-1. The number of EGFP+ cells co-expressing the fibroblastic markers increased with time after puncture. Our findings suggest resident NP cells initially upregulate Col2a1+ and later transform into fibroblast-like cells during injury-mediated disc degeneration and remodelling. This important discovery concerning the cellular origin of fibrotic pathology in injury-induced IDD has implications for management in disease and ageing.

Matrix remodeling during intervertebral disc growth and degeneration detected by multichromatic FAST staining.

Various imaging techniques have been used to assess degeneration of the intervertebral disc, including many histological methods, but cartilage-oriented histological stains do not clearly show the comparatively complex structures of the disc. In addition, there is no integrated method to assess efficiently both the compartmental organization and matrix composition in disc samples. In this study, a novel histological method, termed FAST staining, has been developed to investigate disc growth and degeneration by sequential staining with fast green, Alcian blue, Safranin-O, and tartrazine to generate multichromatic histological profiles (FAST profiles). This identifies the major compartments of the vertebra-disc region, including the cartilaginous endplate and multiple zones of the annulus fibrosus, by specific FAST profile patterns. A disc degeneration model in rabbit established using a previously described puncture method showed gradual but profound alteration of the FAST profile during disc degeneration, supporting continual alteration of glycosaminoglycan. Changes of the FAST profile pattern in the nucleus pulposus and annulus fibrosus of the postnatal mouse spine suggested matrix remodeling activity during the growth of intervertebral discs. In summary, we developed an effective staining method capable of defining intervertebral disc compartments in detail and showing matrix remodeling events within the disc. The FAST staining method may be used to develop a histopathological grading system to evaluate disc degeneration or malformation.

Effect of severity of intervertebral disc injury on mesenchymal stem cell-based regeneration.

Mesenchymal stem cell (MSC) implantation has been shown previously to arrest disc degeneration. This study aims to assess the effect of severity of disc degeneration on the ability of MSCs to arrest the degeneration. Disc degeneration was induced in New Zealand white rabbits at lumbar levels by annular puncture. The degeneration was allowed to progress for 1 month (early group) or 7 months (late group), followed by intradiscal injection of autologous MSCs. For disc levels that received MSCs treatment, 1 x 10(5) BrdU-labeled MSCs were injected per disc level. For the early group, MSC-injection had no significant effects on disc height or the progression of disc degeneration. For the late group, although the MSC-injected discs displayed lower disc heights than the control discs, they were significantly less degenerated together with near normal level of proteoglycan in localized areas. This is the first pilot study to demonstrate that severity of degeneration can influence the therapeutic effect of MSCs. Future studies of cell-based intervertebral disc regeneration should be carefully controlled in the context of stage of disc degeneration.

Histological and reference system for the analysis of mouse intervertebral disc.

A new scoring system based on histo-morphology of mouse intervertebral disc (IVD) was established to assess changes in different mouse models of IVD degeneration and repair. IVDs from mouse strains of different ages, transgenic mice, or models of artificially induced IVD degeneration were assessed. Morphological features consistently observed in normal, and early/later stages of degeneration were categorized into a scoring system focused on nucleus pulposus (NP) and annulus fibrosus (AF) changes. "Normal NP" exhibited a highly cellularized cell mass that decreased with natural ageing and in disc degeneration. "Normal AF" consisted of distinct concentric lamellar structures, which was disrupted in severe degeneration. NP/AF clefts indicated more severe changes. Consistent scores were obtained between experienced and new users. Altogether, our scoring system effectively differentiated IVD changes in various strains of wild-type and genetically modified mice and in induced models of IVD degeneration, and is applicable from the post-natal stage to the aged mouse. This scoring tool and reference resource addresses a pressing need in the field for studying IVD changes and cross-study comparisons in mice, and facilitates a means to normalize mouse IVD assessment between different laboratories. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:233-243, 2018.

Role of SHOX2 in the development of intervertebral disc degeneration.

Intervertebral disc (IVD) degeneration is the most common cause of low back pain, which affect 80% of the population during their lives, with heavy economic burden. Many factors have been demonstrated to participate in IVD degeneration. In this study, we investigated the role of short stature homeobox 2 (SHOX2) in the development of IVD degeneration. First, we detected the expression of SHOX2 in different stages of human IVD degeneration; then explored the role of SHOX2 on nucleus pulposus (NP) cells proliferation and apoptosis, finally we evaluated the effect of SHOX2 on the production of extracellular matrix in NP cells. Results showed that the expression of SHOX2 is mainly in NP compared with AF tissues, its expression decreased with the severity of human IVD degeneration. TNF-α treatment led to dose- and time-dependent decrease in SHOX2 mRNA, protein expression and promoter activity in NP cells. The silencing of SHOX2 inhibited NP cells proliferation and induced NP cells apoptosis. Finally, SHOX2 silencing led to decreased aggrecan and collagen II expression, along with increased ECM degrading enzymes MMP3 and ADAMTS-5 in NP cells. In summary, our results indicated that SHOX2 plays an important role in the process of IVD degeneration, and might be a protective factor for IVD degeneration. Further studies are required to confirm its exact role, and clarify the mechanism. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1047-1057, 2017.

Intervertebral Disc Engineering through Exploiting Mesenchymal Stem Cells: Progress and Perspective.

Intervertebral disc degeneration is a common spinal disorder and may manifest with low back pain or sciatica. The degeneration is characterized by the loss of extracellular matrix integrity and dehydration in the nucleus pulposus. This compromises the viscoelastic property and compressive strength of the disc and therefore the capacity to withstand axial load, eventually causing the disc to collapse or leading to disc bulging or herniation due to abnormal strains on the surrounding annulus. Mesenchymal stem/stromal cells (MSCs) are attractive cell sources for engineering or repair of the disc tissues with respect to their ease of availability and capacity to expand in vitro. Moreover, recent investigations have proposed a potential of MSCs to differentiate into disc-like cells. This review discusses the approaches and concerns for engineering intervertebral disc through manipulating MSCs, with a highlight on the relevance of disc progenitor discovery. Ultimately, stem cell-based engineering of intervertebral disc may facilitate the preservation of motion segment function and address degenerative disc disease in future without spinal fusion.

Cartilage degeneration and excessive subchondral bone formation in spontaneous osteoarthritis involves altered TGF-ß signaling.

Transforming growth factor-ß (TGF-ß) has been demonstrated as a potential therapeutic target in osteoarthritis. However, beneficial effects of TGF-ß supplement and inhibition have both been reported, suggesting characterization of the spatiotemporal distribution of TGF-ß during the whole time course of osteoarthritis is important. To investigate the activity of TGF-ß in osteoarthritis progression, we collected knee joints from Dunkin-Hartley (DH) guinea pigs at 3, 6, 9, and 12-month old (n = 8), which develop spontaneous osteoarthritis in a manner extraordinarily similar to humans. Via histology and micro-computed tomography (CT) analysis, we found that the joints exhibited gradual cartilage degeneration, subchondral plate sclerosis, and elevated bone remodeling during aging. The degenerating cartilage showed a progressive switch of the expression of phosphorylated Smad2/3 to Smad1/5/8, suggesting dual roles of TGF-ß/Smad signaling during chondrocyte terminal differentiation in osteoarthritis progression. In subchondral bone, we found that the locations and age-related changes of osterix(+) osteoprogenitors were in parallel with active TGF-ß, which implied the excessive osteogenesis may link to the activity of TGF-ß. Our study, therefore, suggests an association of cartilage degeneration and excessive bone remodeling with altered TGF-ß signaling in osteoarthritis progression of DH guinea pigs. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:763-770, 2016.

Stem cells and aberrant signaling of molecular systems in skin aging.

The skin is the body's largest organ and it is able to self-repair throughout an individual's life. With advanced age, skin is prone to degenerate in response to damage. Although cosmetic surgery has been widely adopted to rejuvinate skin, we are far from a clear understanding of the mechanisms responsible for skin aging. Recently, adult skin-resident stem/progenitor cells, growth arrest, senescence or apoptotic death and dysfunction caused by alterations in key signaling genes, such as Ras/Raf/MEK/ERK, PI3K/Akt-kinases, Wnt, p21 and p53, have been shown to play a vital role in skin regeneration. Simultaneously, enhanced telomere attrition, hormone exhaustion, oxidative stress, genetic events and ultraviolet radiation exposure that result in severe DNA damage, genomic instability and epigenetic mutations also contribute to skin aging. Therefore, cell replacement and targeting of the molecular systems found in skin hold great promise for controlling or even curing skin aging.