This paper presents a review of the rationale for the in vitro mineralization process, preparation methods, and clinical applications of mineralized collagen. The rationale for natural mineralized collagen and the related mineralization process has been investigated for decades. Based on the understanding of natural mineralized collagen and its formation process, many attempts have been made to prepare biomimetic materials that resemble natural mineralized collagen in both composition and structure. To date, a number of bone substitute materials have been developed based on the principles of mineralized collagen, and some of them have been commercialized and approved by regulatory agencies. The clinical outcomes of mineralized collagen are of significance to advance the evaluation and improvement of related medical device products. Some representative clinical cases have been reported, and there are more clinical applications and long-term follow-ups that currently being performed by many research groups.

Murine C3H10T1/2 cells have many features of mesenchymal stem cells (MSCs). Whether or not the multipotent differentiation capability of C3H10T1/2 cells is comparable to that of primary bone marrow-derived MSCs (BM-MSCs) was investigated in this study. For in vitro osteogenic differentiation, both BM-MSCs and C3H10T1/2 cells differentiated to osteoblastic cell lineage and showed positive staining for alkaline phosphatase (ALP) and increased mRNA expression of Runx2, Col1alphaI, and osteocalcin. C3H10T1/2 cells and BM-MSCs induced similar amounts of bone formation in the biomaterials. Under chondrogenic induction in the presence of TGF-beta1, cell pellets of both BM-MSCs and C3H10T1/2 cells formed cartilage-like tissues with cartilage matrix components including proteoglycan, type II collagen, and aggrecan. However, C3H10T1/2 cells presented lower adipogenic differentiation potential, with only about 10% C3H10T1/2 cells (but about 70% of BM-MSCs) being committed to adipogenesis. In this study we confirmed that C3H10T1/2 cells coimplanted with osteoconductive scaffolds can form bone spontaneously in vivo and that C3H10T1/2 cells have a basal level of osteocalcin expression, suggesting that they may be a good alternative source of primary BM-MSCs for investigating osteogenic and chondrogenic differentiation in bone or cartilage tissue engineering studies. Caution is needed when using C3H10T1/2 cells for adipogenic studies as they appear to have lower adipogenic potential than BM-MSCs.

Atrophic non-union is a serious complication of fractures. The underlying biological mechanisms involved in its pathogenesis are not yet completely understood. MicroRNAs (miRNAs or miRs) are a type of endogenous small non-coding RNA, which participate in various physiological and pathophysiological processes. In this study, differentially expressed miRNAs were screened in patients with atrophic nonunion. In total, 4 miRNAs (miR-149*, miR-221, miR-628-3p and miR-654-5p) were upregulated and 7 miRNAs (let-7b*, miR-220b, miR-513a-3p, miR-551a, miR-576-5p, miR-1236 and kshv-miR-K12-6-5p) were downregulated at the fracture sites in patients with atrophic non-union. Among the upregulated miRNAs, miR-628-3p and miR-654-5p expression was found to be persistently decreased during osteoblast differentiation, indicating their possible inhibitory effect on osteogenesis. Gain-of-function experiment demonstrated that miR-628-3p, but not miR-654-5p, attenuated osteoblast differentiation. Further, in silico analysis revealed that runt-related transcription factor 2 (RUNX2), the master transcript factor for osteoblast differentiation, was the target of miR-628-3p, which had two binding site-condense regions in the 3′ untranslated region. The exact binding site of miR-628-3p was further identified with luciferase reporter assay. In addition, the overexpression of miR-628-3p appeared to be associated with the suppression of RUNX2 expression at both the mRNA and protein level, suggesting that miR-628-3p inhibits osteoblast differentiation via RUNX2. On the whole, the findings of this study provide evidence of the upregulation of miR-628-3p in patients with atrophic non-union and that miR-628-3p may exert an inhibitory effect on osteogenesis via the suppression of its target gene, RUNX2. The study provides valuable insight into the pathogenesis of atrophic non-union and suggests new potential therapeutic targets for the treatment of this disorder.

Object Autophagy is a cellular mechanism of maintaining balance between protein synthesis and degradation; the latter can be induced by starvation and neurodegenerative disease. Spinal cord injury (SCI) induces necrosis and apoptosis. Autophagic flux has not yet been defined, especially the potential role of autophagy in relation to apoptosis in different tissue cells. The object of this study was to investigate the occurrence of autophagic flux and the potential role of autophagy and apoptosis post-SCI in rats. Methods Following creation of SCI in rats, activation of autophagic flux was detected at the protein (LC3, beclin1, and p62) and mRNA (beclin1) levels and on electron microscopy images. Distribution of LC3, colocalization of activated caspase-3, and changes in expression levels of bcl-2 and Bax were assessed to investigate the potential role of autophagy and apoptosis. Sprague-Dawley rats were used, and T9–10 hemitransection was performed. Expression levels of LC3, beclin1, p62, bcl-2, and Bax were assessed by Western blot analysis, and beclin1 mRNA levels were assessed by reverse transcription–polymerase chain reaction. Distribution of LC3 and colocalization of activated caspase-3 were analyzed by immunohistochemistry. Autophagosome formation was investigated by electron microscopy. Results The authors found a dramatic elevation in LC3 and beclin1 levels near the scar region. Using double staining, they observed that upregulation of LC3 started at 4 hours in neurons and at 3 days in astrocytes after SCI. Confocal images indicated that the percentage of neurons with apoptosis was reduced, while the percentage of astrocytes with apoptosis was high at 4 hours, 8 hours, and 1 day post-SCI but decreased sharply at 3 days. Electron microscopy images provided evidence of autophagosome formation. Elimination of p62 indicated occurrence of autophagic flux. Expression levels of bcl-2 and Bax were increased and decreased, respectively, near the injury site. Conclusions The results of this research demonstrated that autophagic flux is activated after SCI. Potentially, inhibition of apoptosis could be a target to promote neural recovery.