This study sought to understand the regulation of an osteoclastic protein-tyrosine phosphatase (PTP-oc), a positive regulator of osteoclast activaty. Our past studies suggested that PTP-oc is regulated post-transcriptionally. The 3'-UTR of PTP-oc mRNA contains a target site for miR17. During osteoclastic differentiation, there was an inverse relationship between the cellular levels of miR17 (expressed as one of the six cluster genes of miR17~92) and PTP-oc mRNA. Overexpression of pre-miR17~92 in mouse osteoclast precursors reduced PTP-oc mRNA level and the size of the derived osteoclasts; whereas deletion of miR17~92 or inhibition of miR17 resulted in the formation of larger osteoclasts containing more nuclei that expressed higher PTP-oc mRNA levels and created larger resorption pits. Thus, PTP-oc-mediated osteoclast activation is modulated in part by miR17~92, particularly miR17. The miR17~92 osteoclast conditional knockout (cKO) mutants, generated by breeding miR17~92loxp/loxp mice with Ctsk-Cre mice, had lower Tb.BV/TV, Tb.BMD, Tb.Conn-Dens, Tb.N, and Tb.Th, but larger Tb.Sp, and greater bone resorption without a change in bone formation compared to littermate controls. The cKO marrow-derived osteoclasts were twice as large, contained twice as many nuclei, and produced twice as large resorption pits as osteoclasts of littermate controls. The expression of genes associated with osteoclast activation was increased in cKO osteoclasts, suggesting that deletion of miR17~92 in osteoclasts promotes osteoclast activation. The cKO osteoblasts did not show differences in cellular miR17 level, alkaline phosphatase activity, and bone nodule formation ability. In conclusion, miR17-92 negatively regulates the osteoclast activity, in part via the miR17-mediated suppression of PTP-oc in osteoclasts.
Vascular calcification (VC) occurs in most otherwise normal individuals over 60 years of age and is intimately linked to hypertension with severe cardiovascular complications, resulting in considerable morbidity and sometimes death. VC is characterized by the deposition of bone tissue within the vessel wall. The cause of VC is unknown although considerable progress has been made in characterizing its pathogenesis. There is direct or indirect evidence for several factors which could contribute to VC including, vitamin K deficiency, magnesium deficiency increased parathyroid hormone, increased serum phosphate, increased BMP activity and microRNAs (a small non-coding RNA molecules). The BMP pathway deserves attention because it is the sine qua non of osteoblast differentiation. With respect to microRNAs, these also could be relevant to the cause of VC because microRNAs are known to influence VC, and importantly, microRNAs can change with age. Here, we used an in vitro model to mimic VC using osteogenic medium in a vascular smooth muscle cell (VSMC) line. From microRNA analysis using quantitative real-time PCR we identified a potential key microRNA, miR-145-5p involved in vascular calcification. Specifically, we found that in our in vitro model of VC has a significant decrease in miR-145-5p expression. In silico analysis revealed that miR-145-5p may bind and regulate SMAD5, which mediates the action of BMP. Accordingly, we found an increase in SMAD5 expression at the mRNA level in VC condition in vitro . Based on the foregoing, we now propose the hypothesis that in young normal individuals, miR-145-5p normally suppresses SMAD5 activity in vasculature; whereas, in aging, miR-145-5p expression is impaired which would result in increasing SMAD5 gene expression, as well as its phosphorylation, which in turn would eventually lead to VC. Thus, miR-145-5p might be a potential therapeutic target to regulate VC in the elderly.
Pluripotent stem cells have the remarkable self-renewal ability and are capable of differentiating into multiple diverse cells.There is increasing evidence that the aging process can have adverse effects on stem cells.As stem cells age, their renewal ability deteriorates and their ability to differentiate into the various cell types is altered.Accordingly, it is suggested aging-induced deterioration of stem cell functions may play a key role in the pathophysiology of the various aging-associated disorders.Understanding the role of the aging process in deterioration of stem cell function is crucial, not only in understanding the pathophysiology of agingassociated disorders, but also in future development of novel effective stem cell-based therapies to treat agingassociated diseases.This review article first focuses on the basis of the various aging disease-related stem cell dysfunction.It then addresses the several concepts on the potential mechanism that causes aging-related stem cell dysfunction.It also briefly discusses the current potential therapies under development for aging-associated stem cell defects.
This study evaluated whether transgenic expression of PTP-oc (osteoclastic transmembrane protein-tyrosine phosphatase) in cells of the osteoclast lineage would affect bone resorption and bone density in young adult mice. Transgenic mice were generated with a transgenic construct using a tartrate-resistant acid phosphatase exon 1C promoter to drive expression of rabbit PTP-oc in osteoclastic cells. pQCT evaluation of femurs of young adult male progeny of three lines showed that transgenic mice had reduced bone volume and area, cortical and trabecular bone mineral content, and density. Histomorphometric analyses at secondary spongiosa of the femur and at metaphysis of the L4 vertebra confirmed that male transgenic mice had decreased trabecular surface, reduced percentage of trabecular area, decreased trabecular number, increased trabecular separation, and increased osteoclast number per bone surface length. Consistent with an increase in bone resorption, the serum C-telopeptide level was 25% higher in transgenic mice than in wild-type littermates. However, the bone phenotype was not readily observed in female young adult transgenic mice. This could in part be due to potential interactions between estrogen and PTP-oc signaling, since the bone loss phenotype was seen in young adult ovariectomized transgenic mice by microcomputed tomography analysis. In vitro, the average pit area per resorption pit created by marrow-derived transgenic osteoclasts was approximately 50% greater than that created by wild-type osteoclasts. Transgenic osteoclasts showed a lower c-Src phosphotyrosine 527 level, greater c-Src kinase activity, and increased tyrosine phosphorylation of paxillin. In summary, this study provides compelling in vivo evidence that PTP-oc is a positive regulator of osteoclasts.
