Zizhao Wu

Endoplasmic reticulum stress-unfolding protein response-apoptosis cascade causes chondrodysplasia in a col2a1 p.Gly1170Ser mutated mouse model.

The collagen type II alpha 1 (COL2A1) mutation causes severe skeletal malformations, but the pathogenic mechanisms of how this occurs are unclear. To understand how this may happen, a col2a1 p.Gly1170Ser mutated mouse model was constructed and in homozygotes, the chondrodysplasia phenotype was observed. Misfolded procollagen was largely synthesized and retained in dilated endoplasmic reticulum and the endoplasmic reticulum stress (ERS)-unfolded protein response (UPR)-apoptosis cascade was activated. Apoptosis occurred prior to hypertrophy, prevented the formation of a hypertrophic zone, disrupted normal chondrogenic signaling pathways, and eventually caused chondrodysplasia. Heterozygotes had normal phenotypes and endoplasmic reticulum stress intensity was limited with no abnormal apoptosis detected. Our results suggest that earlier chondrocyte death was related to the ERS-UPR-apoptosis cascade and that this was the chief cause of chondrodysplaia. The col2a1 p.Gly1170Ser mutated mouse model offered a novel connection between misfolded collagen and skeletal malformation. Further investigation of this mouse mutant model can help us understand mechanisms of type II collagenopathies.

Exogenous Heparan Sulfate Enhances the TGF-β3-Induced Chondrogenesis in Human Mesenchymal Stem Cells by Activating TGF-β/Smad Signaling

Heparan sulfate (HS) interacts with growth factors and has been implicated in regulating chondrogenesis. However, the effect of HS on TGF-β-mediated mesenchymal stem cell (MSC) chondrogenesis and molecular mechanisms remains unknown. In this study, we explored the effects of exogenous HS alone and in combination with TGF-β3 on chondrogenic differentiation of human MSCs and possible signal mechanisms. The results indicated that HS alone had no obvious effects on chondrogenic differentiation of human MSCs and TGF-β/Smad2/3 signal pathways. However, the combined TGF-β3/HS treatment resulted in a significant increase in GAG synthesis, cartilage matrix protein secretion, and cartilage-specific gene expression compared to cells treated with TGF-β3 alone. Furthermore, HS inhibited type III TGF-β receptors (TβRIII) expression and increased TGF-β3-mediated ratio of the type II (TβRII) to the type I (TβRI) TGF-β receptors and phosphorylation levels of Smad2/3. The inhibitor of the TGF-β/Smad signal, SB431542, not only completely inhibited HS-stimulated TGF-β3-mediated Smad2/3 phosphorylation but also completely inhibited the effects of HS on TGF-β3-induced chondrogenic differentiation. These results demonstrate exogenous HS enhances TGF-β3-induced chondrogenic differentiation of human MSCs by activating TGF-β/Smad2/3 signaling.

Melatonin reversed tumor necrosis factor-alpha-inhibited osteogenesis of human mesenchymal stem cells by stabilizing SMAD1 protein.

Tumor necrosis factor‐alpha (TNFα) plays a pivotal role in inflammation‐related osteoporosis through the promotion of bone resorption and suppression of bone formation. Numerous drugs have been produced to treat osteoporosis by inhibiting bone resorption, but they offer few benefits to bone formation, which is what is needed by patients with severe bone loss. Melatonin, which can exert both anti‐inflammatory and pro‐osteogenic effects, shows promise in overcoming TNFα‐inhibited osteogenesis and deserves further research. This study demonstrated that melatonin rescued TNFα‐inhibited osteogenesis of human mesenchymal stem cells and that the interactions between SMURF1 and SMAD1 mediated the crosstalk between melatonin signaling and TNFα signaling. Additionally, melatonin treatment was found to downregulate TNFα‐induced SMURF1 expression and then decrease SMURF1‐mediated ubiquitination and degradation of SMAD1 protein, leading to steady bone morphogenetic protein‐SMAD1 signaling activity and restoration of TNFα‐impaired osteogenesis. Thus, melatonin has prospects for treating osteoporosis caused by inflammatory factors due to its multifaceted functions on regulation of bone formation, bone resorption, and inflammation. Further studies will focus on unveiling the specific mechanisms by which melatonin downregulates SMURF1 expression and confirming the clinical therapeutic value of melatonin in the prevention and therapy of bone loss associated with inflammation.

Melatonin‐mediated miR‐526b‐3p and miR‐590‐5p upregulation promotes chondrogenic differentiation of human mesenchymal stem cells

Bone marrow‐derived mesenchymal stem cells (BMSCs), with inherent chondrogenic differentiation potential appear to be ideally suited for therapeutic use in cartilage regeneration. Accumulating evidence has demonstrated that melatonin can promote chondrogenic differentiation in human BMSCs. However, little is known about the mechanism. MicroRNAs (miRNAs) have been shown to regulate the differentiation of BMSCs, but their roles in melatonin‐promoted chondrogenic differentiation have not been characterized. Here, we demonstrate that melatonin promoted chondrogenic differentiation of human BMSCs via upregulation of miR‐526b‐3p and miR‐590‐5p. Mechanistically, the elevated miR‐526b‐3p and miR‐590‐5p enhanced SMAD1 phosphorylation by targeting SMAD7. Additionally, administration of miR‐526b‐3p mimics or miR‐590‐5p mimics successfully promoted the chondrogenic differentiation of human BMSCs. Collectively, our study suggests that modification of BMSCs using melatonin or miRNA transduction could be an effective therapy for cartilage damage and degeneration.

Rare coding variants in MAPK7 predispose to adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a complex genetic disorder characterized by three‐dimensional spinal curvatures, affecting 2%–3% of school age children, yet the causes underlying AIS are not well understood. Here, we first conducted a whole‐exome sequencing and linkage analysis on a three‐generation Chinese family with autosomal‐dominant (AD) AIS, and then performed targeted sequencing in a discovery cohort comprising 20 AD AIS families and 86 simplex patients, and finally identified three disease‐associated missense variants (c.886G> A, c.1943C> T, and c.1760C> T) in the MAPK7 gene (encoding mitogen‐activated protein kinase 7). Genotyping of the three rare variants in a Chinese replication cohort comprising 1,038 simplex patients and 1,841 controls showed that their combined allele frequency was significantly over‐represented in patients as compared with controls (2.0% [41/2,076] vs. 0.7% [27/3,682]; odds ratio = 2.7; P = 2.8 × 10−5). In vitro, we demonstrated that the three MAPK7 mutants disrupted nuclear translocation in cellular models, which is necessary for the normal function of MAPK7. In vivo, we also conducted CRISPR/Cas9‐mediated deletion of mapk7 in zebrafish recapitulating the characteristic phenotype of idiopathic scoliosis. Taken together, our findings suggest that rare coding variants in MAPK7 predispose to AIS, providing clues to understanding the mechanisms of AIS.

Collagen type II is downregulated in the degenerative nucleus pulposus and contributes to the degeneration and apoptosis of human nucleus pulposus cells

Degenerative disc disease (DDD) is a common degenerative condition initiated mainly within the nucleus pulposus (NP). To date, the etiopathogenesis of DDD remains unclear, and because no effective therapeutic strategies are available to target its pathological processes, DDD is still treated with symptomatic interventions that are far from adequate. Collagen type II is one of the major matrix components of the NP, and is considered to be essential to NP homeostasis. However, the specific mechanisms by which collagen type II influences NP cells remain unknown. In the present study, collagen type II expression was detected using immunohistochemistry analysis and quantitative polymerase chain reaction, and it was demonstrated to be significantly downregulated in NP tissues from patients with DDD compared with nondegenerative controls. To further explore the mechanism in vitro, interleukin (IL)-1β stimulation was used to induce degeneration of a human NP cell line. IL-1β stimulation upregulated both the mRNA and protein levels of the catabolic markers matrix metalloproteinase 13 (MMP13) and a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS4), while it downregulated the anabolic makers aggrecan and collagen type II. However, addition of purified collagen type II prevented this IL-1β-induced metabolic disturbance of the NP cells. Furthermore, IL-1β stimulation significantly promoted apoptosis in NP cells, while collagen type II treatment decreased the apoptotic rate and the protein levels of cleaved caspase-3. In conclusion, collagen type II exhibited protective effects in suppressing NP cell degeneration through its anticatabolic, proanabolic and antiapoptotic effects, suggesting that it may be a promising therapeutic agent for the prevention and treatment of DDD.