Intermittent cyclic mechanical compression promotes endplate chondrocytes degeneration by disturbing Nrf2/PINK1 signaling pathway-dependent mitophagy.

An abnormal mechanical load is a pivotal inducer of endplate cartilage degeneration, which subsequently promotes intervertebral disc degeneration. Our previous study indicated that intermittent cyclic mechanical compression (ICMC) promotes endplate chondrocyte degeneration, but the mechanism underlying this effect is unclear. In this study, we investigated PTEN-induced kinase 1(PINK1) dependent mitophagy during ICMC-induced endplate chondrocyte degeneration. Furthermore, we determined whether NF-E2-related factor 2 (Nrf2) activation correlated with PINK1-dependent mitophagy regulation and increased oxidation resistance of endplate chondrocytes under ICMC application. First, we generated a mechanical compression-induced endplate chondrocyte degeneration model in vitro and in vivo. ICMC was found to promote endplate chondrocyte extracellular matrix degradation. PINK1-mediated mitophagy was suppressed in the ICMC-stimulated endplate chondrocytes, while increased mitochondrial reactive oxygen species generation suggested that mitophagy is involved in the protective effect of mechanical strain on endplate chondrocytes. Moreover, Nrf2 expression, interaction with Kelch-like ECH-associated protein (Keap1), and nuclear translocation were inhibited by ICMC. Nrf2 overexpression inhibited reactive oxygen species production and reversed ICMC-induced endplate chondrocyte degeneration. Transfection with PINK1 shRNA abolished this effect and partially blocked Nrf2-induced mitophagy. Our findings suggested that ICMC could inhibit the Nrf2/PINK1 signaling pathway to reduce the mitophagy levels which significantly promote oxidative stress and thereby endplate chondrocyte degeneration. Therapeutic regulation of the Nrf2/PINK1 signaling pathway may be an efficient anabolic strategy for inhibiting this process.

[Treatment of intertrochanteric fracture of femur with closed reduction of proximal femoral anti rotation intramedullary nail in supine position].

OBJECTIVE: To investigate the effect and feasibility of closed reduction and internal fixation with PFNA in the treatment of intertrochanteric fracture of femur in the supine position without traction bed. METHODS: From June 2014 to March 2018, 45 patients with intertrochanteric fracture of femur who were treated and followed up were analyzed retrospectively. There were 21 males and 24 females, with an average age of 67.4 years (43 to 92 years);18 cases on the left side and 27 on the right side. According to Evans Jensen classification, there were 7 patients of type Ⅱ, 17 patients of type Ⅲ, 16 patients of type Ⅳ and 5 patients of type Ⅴ. The time from injury to operationwas 2 to 6 days. The operation time, blood loss and fracture healing, closing time, postoperative complications and Harris score of hip joint were recorded. RESULTS: The operation time of 45 patients was 35 to 80 min, with an average of 52.6 min;the intraoperative bleeding volume was 40 to 110 ml, with an average of 68.7 ml;the hospitalization time was 6 to 11 days, with an average of 8.4 days;the follow up time was 12 to 18 months, with an average of 14.7 months;the internal fixation of 2 patients failed, and 43 patients achieved bony healing;the deep vein thrombosis of the lower extremity in the perioperative period was 1 case, and the inferior vena cava filter was inserted;the internal fixation of 2 patients was cut out, and the hip was renovated. The incidence of complications was 8.9%(4 / 45). At the final follow up, Harris score of hip joint was 56 to 95 (81.30±8.40), including excellent 15 cases, good 26 cases, fair 2 cases and poor 2 cases. CONCLUSION: It is safe and feasible to treat intertrochanteric fracture of femur with closed reduction and anti rotation intramedullary nailing under the bed without traction in a supine position. It has the advantages of small trauma and low complications, and the clinical effect is satisfactory. It is worth popularizing and using in basic hospitals.

MicroRNA-365 functions as a mechanosensitive microRNA to inhibit end plate chondrocyte degeneration by targeting histone deacetylase 4.

End plate chondrocyte degeneration is a major cause of intervertebral disc degeneration. Mechanical biophysical forces, including intermittent cyclic mechanical tension (ICMT), exacerbate end plate chondrocyte degeneration. However, the underlying molecular mechanism of mechanical stretch-induced end plate chondrocyte degeneration is still unclear. This study sought to determine whether microRNAs (miRNAs) respond to mechanical stretch and play a role in regulating mechanically-induced end plate chondrocyte degeneration. We identified miR-365 as a mechanoresponsive miRNA in primary human end plate chondrocytes after ICMT application by miRNA microarray analysis. The expression of miR-365 was down-regulated in the disc samples obtained from patients with disc degeneration. We also found that the miR-365 stimulates chondrocyte proliferation but does not promote end plate chondrocyte death. Using bioinformatic analyses and subsequent confirmation by real-time RT-PCR, we identified multiple candidate target genes of miR-365 that responded to in vitro mechanical stimulation; among them, HDAC4 was fully characterized. Mutation of putative miR-365 binding sites in HDAC4 mRNA abolished miR-365 mediated repression of HDAC4 3'-untranslated region (3'UTR) luciferase reporter activity, suggesting that miR-365 binds to the HDAC4 3'UTR. Overexpression of miR-365 significantly decreased the HDAC4 protein level, suggesting that miR-365 acts as an endogenous attenuator of HDAC4 in human end plate chondrocytes. Further, perturbation of miR-365 expression also had a significant effect on the expression of COL2A and ACAN and on matrix degeneration. Overexpression of HDAC4 abolished miR-365 rescued end plate chondrocyte degeneration during ICMT application. Furthermore, we found that the wnt/ß-catenin signal pathway was related to HDAC4 and promoted end plate chondrocyte degeneration. Overall, our results suggest that miR-365 is a mechanosensitive miRNA that regulates human chondrocyte degeneration by directly targeting HDAC4. We propose that therapeutic regulation of miR-365 may be an efficient anabolic strategy for inhibiting end plate chondrocyte degeneration.