Sex-specific response of intramuscular fat to diet-induced obesity in rats.

Metabolic abnormalities associated with excess adiposity in obesity contribute to many noncommunicable diseases, including sarcopenic obesity. Sarcopenic obesity is the loss of muscle mass coupled with excess fat mass and fatty infiltrations in muscle tissue called myosteatosis. A diet-induced obesity model was developed to study fat infiltration in muscle tissue. Only male rats have been considered in these investigations neglecting that female rats might respond differently. The objective of this study was to determine if the response to diet-induced obesity can be generalized to both sexes, or whether sex affects the response to the HFS diet, as indicated by markers of metabolic syndrome and changed in muscle integrity. Using a combination of histological staining techniques, quantitative proteomics, and measures of metabolic syndrome and inflammation, it was determined that the diet-induced obesity model in female Sprague-Dawley rats is a viable model with pronounced effects on the musculoskeletal system. We found sex-dependent and muscle-specific differences in intramuscular fat infiltration between male and female rats receiving the obesogenic diet. Including females in research may allow for identifying distinct causes of the mechanistic relationship between diet, obesity, metabolic syndrome, and the sex-dependent differential effects of these factors on adaptation and degeneration of musculoskeletal tissues.