Impairment of Cyclo-oxygenase-2 Function Results in Abnormal Growth Plate Development and Bone Microarchitecture but Does Not Affect Longitudinal Growth of the Long Bones in Skeletally Immature Mice

Inositol 1,4,5-trisphosphate receptor type 2 is associated with the bone-vessel axis in chronic kidney disease-mineral bone disorder

Objective: The pathogenesis of renal osteopathy and cardiovascular disease suggests the disordered bone-vessel axis in chronic kidney disease-mineral bone disorder (CKD-MBD). However, the mechanism of the bone-vessel axis in CKD-MBD remains unclear.Methods: We established a CKD-MBD rat model to observe the pathophysiological phenotype of the bone-vessel axis and performed RNA sequencing of aortas to identify novel targets of the bone-vessel axis in CKD-MBD.Results: The microarchitecture of the femoral trabecular bone deteriorated and alveolar bone loss was aggravated in CKD-MBD rats. The intact parathyroid hormone and alkaline phosphatase levels increased, 1,25-dihydroxyvitamin D3 levels decreased, and intact fibroblast growth factor-23 levels did not increase in CKD-MBD rats at 16 weeks; other bone metabolic parameters in the serum demonstrated dynamic characteristics. With calcium deposition in the abdominal aortas of CKD-MBD rats, RNA sequencing of the aortas revealed a significant decrease in inositol 1,4,5-trisphosphate receptor type 2 (ITPR2) gene levels in CKD-MBD rats. A similar trend was observed in rat aortic smooth muscle cells. As a secretory protein, ITPR2 serum levels decreased at 4 weeks and slightly increased without statistical differences at 16 weeks in CKD-MBD rats. ITPR2 serum levels were significantly increased in patients with vascular calcification, negatively correlated with blood urea nitrogen levels, and positively correlated with serum tartrate-resistant acid phosphatase 5b levels.Conclusion: These findings provide preliminary insights into the role of ITPR2 in the bone-vessel axis in CKD-MBD. Thus, ITPR2 may be a potential target of the bone-vessel axis in CKD-MBD.

Cisplatin triggers oxidative stress, apoptosis and pro-inflammatory responses by inhibiting the SIRT1-mediated Nrf2 pathway in chondrocytes

Although the height of the proliferating layer that was suppressed in the growth plate has been recognized as an adverse effect of cisplatin in pediatric cancer survivors, the detailed pathological mechanism has not been elucidated. Sirtuin-1 (SIRT1) has been reported as an essential modulator of cartilage homeostasis, but its role in cisplatin-induced damage of chondrocytes remains unclear. In this study, we examined how cisplatin affected the expression of SIRT1 and cell viability. Next, we showed downregulation of SIRT1 after cisplatin treatment resulted in suppression of Peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α), leading to inhibition of Nrf2 nuclear translocation and subsequently decreased Heme oxygenase-1(HO-1) and NAD(P)H Quinone Dehydrogenase 1(NQO-1) expression. Blockage of the SIRT1/ PGC-1α axis not only increased oxidative stress with lower antioxidant SOD and GSH, but also contributed to mitochondrial dysfunction evidenced by the collapse of membrane potential and repression of mitochondrial DNA copy number and ATP. We also found that Cisplatin up-regulated the p38 phosphorylation, pro-inflammatory events and matrix metalloproteinases (MMPs) in chondrocytes through the SIRT1-modulated antioxidant manner. Collectively, our findings suggest that preservation of SIRT1 in chondrocytes may be a potential target to ameliorate growth plate dysfunction for cisplatin-receiving pediatric cancer survivors.

Integrin expression and extracellular matrix adhesion of septoclasts, pericytes, and endothelial cells at the chondro-osseous junction and the metaphysis of the proximal tibia in young mice

We previously reported that septoclasts, which are uncalcified growth plate (GP) cartilage matrix-resorbing cells, are derived from pericytes surrounding capillary endothelial cells. Resorption of the GP is assumed to be regulated synchronously by septoclasts, pericytes, and endothelial cells. To reveal the contribution of the extracellular matrix (ECM) to the regulatory mechanisms of septoclastic cartilage resorption, we investigated the spatial correlation between the cells and the ECM in the GP matrix and basement membrane (BM) and investigated the expression of integrins-ECM receptors-in the cells. Septoclasts attached to the transverse septa containing collagen-II/-X at the tip of their processes and to the longitudinal septa containing collagen-II/-X at the spine-like processes extending from their bodies and processes. Collagen-IV and laminin α4 in the BM were sparsely detected between septoclasts and capillary endothelial cells at the chondro-osseous junction (COJ) and were absent in the outer surface of pericytes at the metaphysis. Integrin α1/α2, integrin α1, and integrin α2/α6 were detected in the cell membranes of septoclasts, pericytes, and endothelial cells, respectively. These results suggest that the adhesion between septoclasts and the cartilage ECM forming the scaffolds for cartilage resorption and migration is provided by integrin α2-collagen-II/-X interaction and that the adhesions between the BM and pericytes or endothelial cells are mediated by integrin α1-collagen-IV and integrin α2/α6-laminin interaction, respectively.

Combining phosphate binder therapy with vitamin K2 inhibits vascular calcification in an experimental animal model of kidney failure

BACKGROUND

Hyperphosphataemia is strongly associated with cardiovascular disease and mortality. Recently, phosphate binders (PBs), which are used to bind intestinal phosphate, have been shown to bind vitamin K, thereby potentially aggravating vitamin K deficiency. This vitamin K binding by PBs may offset the beneficial effects of phosphate reduction in reducing vascular calcification (VC). Here we assessed whether combining PBs with vitamin K2 supplementation inhibits VC.

METHODS

We performed 3/4 nephrectomy in rats, after which warfarin was given for 3 weeks to induce vitamin K deficiency. Next, animals were fed a high phosphate diet in the presence of low or high vitamin K2 and were randomized to either control or one of four different PBs for 8 weeks. The primary outcome was the amount of thoracic and abdominal aorta VC measured by high-resolution micro-computed tomography (µCT). Vitamin K status was measured by plasma MK7 levels and immunohistochemically analysed in vasculature using uncarboxylated matrix Gla protein (ucMGP) specific antibodies.

RESULTS

The combination of a high vitamin K2 diet and PB treatment significantly reduced VC as measured by µCT for both the thoracic (P = 0.026) and abdominal aorta (P = 0.023), compared with MK7 or PB treatment alone. UcMGP stain was significantly more present in the low vitamin K2-treated groups in both the thoracic (P < 0.01) and abdominal aorta (P < 0.01) as compared with high vitamin K2-treated groups. Moreover, a high vitamin K diet and PBs led to reduced vascular oxidative stress.

CONCLUSION

In an animal model of kidney failure with vitamin K deficiency, neither PB therapy nor vitamin K2 supplementation alone prevented VC. However, the combination of high vitamin K2 with PB treatment significantly attenuated VC.

Evaluation of impaired growth plate development of long bones in skeletally immature mice by antirheumatic agents

Restriction of physical growth and development is a known problem in patients with juvenile idiopathic arthritis (JIA). However, the effect of medical treatment for JIA on skeletal growth in affected children has not been properly investigated. We, therefore, hypothesize that naproxen and methotrexate (MTX) affect endochondral ossification and will lead to reduced skeletal development. Treatment of ATDC5 cells, an in vitro model for endochondral ossification, with naproxen or MTX resulted in increased chondrogenic but decreased hypertrophic differentiation. In vivo, healthy growing C57BL/6 mice were treated with naproxen, MTX, or placebo for 10 weeks. At 15 weeks postnatal, both the length of the tibia and the length of the femur were significantly reduced in the naproxen- and MTX-treated mice compared to their controls. Growth plate analysis revealed a significantly thicker proliferative zone, while the hypertrophic zone was significantly thinner in both experimental groups compared to their controls, comparable to the in vitro results. Micro-computed tomography analysis of the subchondral bone region directly below the growth disc showed significantly altered bone microarchitecture in naproxen and MTX groups. In addition, the involvement of the PTHrP-Ihh loop in naproxen- and MTX-treated cells was shown. Overall, these results demonstrate that naproxen and MTX have a profound effect on endochondral ossification during growth plate development, abnormal subchondral bone morphology, and reduced bone length. A better understanding of how medication influences the development of the growth plate will improve understanding of endochondral ossification and reveal possibilities to improve the treatment of pediatric patients.