Bone and skeletal muscle work in coordination to maintain the function of the musculoskeletal system, in which skeletal muscle contraction drives the movement of the bone lever system while bone provides insert sites for skeletal muscle through the bone-muscle junction. Existing evidence suggests that factors secreted by skeletal muscle and bone mediate the interaction between the two tissues. Herein, we focused on the relationship between skeletal muscle and bone and the underlying mechanism of the interaction. Exercise can promote bone strength and secrete osteocalcin and insulin-like growth factor I into the blood, thus improving muscle quality. In addition, exercise can also promote myostatin, interleukin-6, Irisin, and apelin in muscles to enter the blood so that they can act on bones to maintain the balance between bone absorption and bone formation. There is a special regulatory axis interleukin-6/osteocalcin between myokines and osteokines, which is mainly influenced by exercise. Therefore, we pay attention to the important factors in the bone-muscle intersection that are affected by exercise, which were found or their functions were expanded, which strengthened the connection between organs of the whole body, highlighting the importance of exercise and contributing to the diagnosis, prevention, and treatment of osteoporosis and sarcopenia in the clinic.

Osteoclasts are giant bone-digesting cells that harbor specialized lysosome-related organelles termed secretory lysosomes (SLs). SLs store cathepsin K and serve as a membrane precursor to the ruffled border, the osteoclast’s ‘resorptive apparatus’. Yet, the molecular composition and spatiotemporal organization of SLs remains incompletely understood. Here, using organelle-resolution proteomics, we identify member a2 of the solute carrier 37 family (Slc37a2) as a SL sugar transporter. We demonstrate in mice that Slc37a2 localizes to the SL limiting membrane and that these organelles adopt a hitherto unnoticed but dynamic tubular network in living osteoclasts that is required for bone digestion. Accordingly, mice lacking Slc37a2 accrue high bone mass owing to uncoupled bone metabolism and disturbances in SL export of monosaccharide sugars, a prerequisite for SL delivery to the bone-lining osteoclast plasma membrane. Thus, Slc37a2 is a physiological component of the osteoclast’s unique secretory organelle and a potential therapeutic target for metabolic bone diseases.

To investigate the underlying mechanisms of low metabolic activity of primary chondrocytes obtained from girls with adolescent idiopathic scoliosis (AIS); AIS is a spine-deforming disease that often occurs in girls. AIS is associated with a lower bone mass than that of healthy individuals and osteopenia. Leptin was shown to play an important role in bone growth. It can also regulate the function of chondrocytes. Changes in leptin and Ob-R levels in AIS patients have been reported in several studies. The underlying mechanisms between the dysfunction of peripheral leptin signaling and abnormal chondrocytes remain unclear; The following parameters were evaluated in AIS patients and the control groups: total serum leptin levels; Ob-R expression in the plasma membrane of primary chondrocytes; JAK2 and STAT3 phosphorylation status. Then, we inhibited the lysosome and proteasome and knocked down clathrin heavy chain (CHC) expression in primary chondrocytes isolated from girls with AIS and evaluated Ob-R expression. We investigated the effects of leptin combined with a lysosome inhibitor or CHC knockdown in primary chondrocytes obtained from AIS patients; Compared with the controls, AIS patients showed similar total serum leptin levels, reduced JAK2 and STAT3 phosphorylation, and decreased cartilage matrix synthesis in the facet joint. Lower metabolic activity and lower membrane expression of Ob-R were observed in primary chondrocytes from the AIS group than in the controls. Lysosome inhibition increased the total Ob-R content but had no effect on the membrane expression of Ob-R or leptin’s effects on AIS primary chondrocytes. CHC knockdown upregulated the membrane Ob-R levels and enhanced leptin’s effects on AIS primary chondrocytes; The underlying mechanism of chondrocytes that are hyposensitive to leptin in some girls with AIS is low plasma membrane Ob-R expression that results from an imbalance between the rate of receptor endocytosis and the insertion of newly synthesized receptors into the membrane.

Background: How to treat the posterior cruciate ligament (PCL) tibial insertion small and comminuted avulsion fracture is still challenging. Our study evaluated the clinical and radiological outcomes after ORIF of PCL tibial insertion avulsion fractures through the inverted L-shaped postero-medial approach using a homemade pin-hook. Methods: Between January 2009 and December 2020, twenty-four patients with isolated PCL tibial insertion bony avulsion were enrolled. There were 16 males and 8 females. The age range was 18-48 (32.5 ± 9.3) years. The time from injury to surgery was 1-10 (4.4 ± 2.8) days. There were 11 cases in the left knee and 13 cases in the right knee. The patients received anticoagulant therapy to prevent thrombosis. Preoperative standard X-ray, computerized tomography (CT) and magnetic resonance imaging (MRI) were performed. According to the Meyers-McKeever classification, there were 8 cases of type II and 16 cases of type III. Results: The operation time was 60-120 (89.6 ± 19.8) min. Postoperative follow-up ranged from 3 to 18 months. The average follow-up was 11.4 ± 4.3 months. In all patients, one or two homemade pin-hooks were used to fix different sizes of fracture segments. X-ray or CT scans taken after surgery revealed fracture union. The fractures healed in 9-16 (11.8 ± 1.7) weeks. At the last follow-up, the patients were able to fully straighten. The ROM (132.6° ± 3.9°), the Tegner-Lysholm score (96.2 ± 2.3) and the IKDC scores (95.5 ± 1.6) were all significantly improved compared with the preoperative values (77.5° ± 13.1°, 46.8 ± 8.9, 36.2 ± 7.9). The posterior drawer test was negative. The gastrocnemius muscle strength did not diminish. No internal fixation migration was observed during the follow-up. No neurovascular bundle- or hardware-related complications were reported. Conclusions: The inverted L-shaped postero-medial approach with homemade pin-hook fixation for the treatment of PCL avulsion fractures produces acceptable clinical and radiological results. Moreover, the homemade pin-hook made of K-wires is affordable and reduces patient costs. It is a practical application and worth recommending, especially for community hospitals.