TNF-α suppresses osteogenic differentiation of MSCs by accelerating P2Y2 receptor in estrogen-deficiency induced osteoporosis.

Tumor Necrosis Factor-α (TNF-α)-inhibited osteogenic differentiation of mesenchymal stem cells (MSCs) contributes to impaired bone formation, which plays a central role in the pathogenesis of postmenopausal osteoporosis. However, the exact mechanisms of TNF-α-inhibited osteoblast differentiation have not been fully elucidated. Multiple P2 purinoceptor subtypes are expressed in several species of osteoblasts and are confirmed to regulate bone metabolism. The purpose of this study is to investigate whether P2 purinoceptors are involved in TNF-α-inhibited osteoblast differentiation. This study shows TNF-α increased P2Y2 receptor expression in the differentiation of MSCs into osteoblasts in a noticeable manner. Overexpressing or silencing of the P2Y2 receptor either impaired or promoted osteogenic differentiation of MSCs significantly. Silencing of the P2Y2 receptor attenuated the inhibitory effects of TNF-α on osteoblastic differentiation of MSCs. In addition, silencing of the P2Y2 receptor evidently alleviated TNF-α-inhibited MSC proliferation. P2Y2 receptor expression was mechanistically upregulated by TNF-α mainly through extracellular regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways. Overall, our results revealed a novel function of the P2Y2 receptor and suggested suppressing the P2Y2 receptor may be an effective strategy to promote bone formation in estrogen deficiency-induced osteoporosis.

[Changes of endogenous Spastin expression after sciatic nerve injury in rats].

Objective: To investigate the expression change of endogenous Spastin after sciatic nerve injury in rats, and to discuss the role and significance in the peripheral nerve regeneration. Methods: Thirty-six adult male Sprague Dawley rats weighing 180-220 g were randomly divided into the experimental group ( n=30) and the control group ( n=6). Sciatic nerve compression damage model was established in the experimental group, and the sciatic nerve was only exposed in the control group. The L 4-6 spinal cord tissue was obtained to detect Spastin mRNA and protein levels by real-time fluorescence quantitative PCR and Western blot at 1, 3, 7, 14, and 28 days after operation in the experimental group ( n=6) and at 7 days in the control group. Meanwhile, the sciatic nerve at 5 mm distal to the injured site was obtained to observe the ultrastructure of the distal axon by transmission electron microscope (TEM). Results: The expression trends of Spastin gene and Spastin protein in L 4-6 spinal cord tissue of 2 groups were basically identical. In the experimental group, the expressions of Spastin gene and protein decreased at the beginning, and then increased; the expressions reduced to the minimum at 7 days after operation, and came back to the initial level at 28 days. The expression levels of Spastin mRNA and protein at 3, 7, and 14 days were significantly lower in the experimental group than the control group ( P<0.05), but no significant difference was noted between 2 groups at 1 and 28 days ( P>0.05). The expression levels of Spastin mRNA and protein at 3, 7, and 14 days were significantly lower than those at 1 and 28 days in the experimental group ( P<0.05), but no significant difference was noted between at 1 day and 28 days ( P>0.05). At 1, 3, and 7 days after operation, the myelin damage was observed by TEM; at 14 days, there were regenerating Schwann cells; at 28 days, a large number of myelinated nerve fibers were seen, which were closed to normal form. Conclusion: In the process of sciatic nerve regeneration after injury, a complex succession of changes take place in the expression of endogenous Spastin protein in rats, indicating that Spastin protein plays an important role in the process.