Background/Purpose:  Age-related accumulation of muscular fat and loss of muscle mass contribute to impaired muscle function and consequent mobility impairment in older adults. These muscle changes may result from excess ectopic fat accumulation, which produces inflammatory cytokines that promote differentiation of muscle satellite cells into adipocytes versus myoblasts. It is unknown whether this muscle-fat cross-talk occurs primarily via systemic effects of circulating cytokines, or through paracrine effects between adjacent compartments. Our objective was to determine the association of peri-aortic adipose tissue (PAAT) volume with size and fat content of adjacent trunk muscles among 948 participants (56% women) in the community-based Framingham Study.

Methods:  Multidetector CT abdominal imaging measured PAAT volume (cm³), as well as cross-sectional area (mm²) and attenuation (HU), a marker of fat content, of the erector spinae, transversospinalis, and trapezius muscles at the T7 and T8 levels. Cross-sectional area and attenuation of each muscle was averaged for the left and right sides, and across vertebral levels. Linear regression was used to calculate coefficients (β) estimating the associations of PAAT volume with muscle cross-sectional area and attenuation, adjusting for sex, age, height, body mass index (BMI) and self-reported physical activity (Framingham Physical Activity Index). Models were further adjusted for abdominal visceral (VAT) and subcutaneous adipose tissue (SAT) volumes (cm³), measured from the same CT images, to determine if PAAT associations were independent of abdominal fat depots.

Results:  Mean age was 58 years (range 45-81), mean BMI was 28 kg/m² (range 18-53). While there was no association with muscle cross sectional area (β=-0.96, P=0.37), PAAT was inversely associated with muscle attenuation (β=-0.31, P<0.0001), indicating greater muscle fat content with increasing PAAT. The association remained after further adjustment for VAT (β for PAAT=-0.21, P<0.0001) and SAT (β for PAAT=-0.33, P<0.0001). Results were similar when stratified by sex and categorizing PAAT as quartiles.

Conclusion:   We found that increased fat surrounding the aorta was associated with greater fat content in nearby trunk muscles, independent of overall obesity and specific abdominal fat depot volumes. PAAT was not, however, associated with trunk muscle size. Our findings suggest that age-related fat accumulation in skeletal muscle may result mainly from local paracrine effects of adjacent fat depots. Cross-talk between neighboring fat and muscle is a potential novel target for therapies aiming to prevent or restore loss of muscle function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/peri-aortic-adipose-tissue-volume-is-directly-associated-with-fat-accumulation-in-adjacent-trunk-muscles-independent-of-other-fat-depots-the-framingham-study/