Bone and muscle closely interacted anatomically, chemically, and metabolically. Various muscle-derived humoral factors, known as myokines, affect bone. Extracellular vesicles (EVs) play a vital role in physiological and pathophysiological processes by transferring their contents to distant tissues, including bone metabolism. However, the amount and cargo of released EVs, consisting of microRNAs (miRNAs), mRNA, proteins, and DNA, are altered in obesity. Therefore, the roles of EVs in muscle-bone interactions in obesity remain unknown. The present study investigated the effects of EVs secreted from obese and lean mice muscles on bone cells, strength, and quality.
EVs were isolated from muscle samples of leptin receptor mutant db/db mice (obese) and myostatin null mice (lean) to determine the size, concentration, and miRNA profile. EVs were stained with CD63 and visualized under Electron Microscopy. In addition, femurs and tibias were extracted for micro-CT, 3-point bending, and bone histomorphometry. Furthermore, bones were stained for adiponectin, PPAR gamma, and perilipin RNA levels by RNA scope.
Compared to lean mice, muscle-derived EVs obtained from db/bd mice showed significant upregulation (3.5 fold) of mir-465 miRNA, which associates with three genes (CDC37, DAPK1, and Tirap). These genes are associated with Leucine-Rich Repeat Kinase 1 (LRRK1), a vital regulator of osteoclastogenesis. In addition, LRRK1 levels were significantly higher in femurs of db/db mice than in lean mice. Furthermore, we showed that db/db mice had a 23% increase in osteoclast numbers and a 10% decrease in osteoblast numbers compared to lean mice. Furthermore, we showed that db/db mice had significantly lower bone quality by micro-CT and 3-point bending compared to lean mice. Lastly, db/db mice also showed increased adiponectin, PPAR gamma, and perilipin RNA levels compared to lean mice.
In conclusion, these findings suggest that muscle EVs from obese mice directly impact bone cells and quality via their microRNA cargo.