Obesity Alters Adipogenesis Regulation in Human Skeletal Muscle

Introduction: : Intramuscular fatty accumulation is a hallmark of obesity and skeletal muscle pathologies, leading to muscle dysfunction and functional decline. Fibroadipogenic progenitors (FAPs), a mesenchymal progenitor cell population in muscle tissue, are a key source of fatty infiltration due to their adipogenic potential. Recent studies have identified a CD142⁺ subpopulation, termed adipogenesis regulators (Aregs), which suppressed adipocyte differentiation in both adipose tissue and skeletal muscle. However, the interactions between Aregs and FAPs remain poorly understood. We hypothesize that obesity alters Areg function and secretomes in skeletal muscle leading to increased FAP adipogenesis and fatty infiltration.

Materials and

Methods: : Human skeletal muscle samples (n=51, 21 females, 30 males) were obtained from patients who were undergoing internal fixation of limb fractures or anterior cruciate ligament (ACL) reconstruction surgeries. Patients ranged from 18 to 86 years old (mean 35.5 ± 13.5 years) with BMIs from 18.1 to 47.4 kg/m² (mean 27.7 ± 5.9 kg/m²; normal weight: 18.5–24.9, overweight: 25–29.9, obese: ≥30). No statistical differences were observed between age and BMI groups (One-Way Anova; p=0.3119). Aregs (CD142⁺CD140a⁺CD140b⁺) and FAPs (CD142⁻CD140a⁺CD140b⁺) were sorted via flow cytometry. Adipogenic differentiation was induced for 14 days. A novel device (ParaTalk, Fig. 1A-C), designed and printed in-house, was used to investigate paracrine interaction between Aregs and FAPs.

Results, Conclusions, and Discussions:: We identified a CD142⁺ subpopulation within skeletal muscle FAPs co-expressing FAP markers CD140a and CD140b by flow cytometry. Obese individuals exhibited ~2-fold more Aregs (n=21, p=0.04) with increased proliferation rates compared to normal-weight individuals (n=4, 7% increase, p=0.05). Adipogenic differentiation assays had a negative correlation between CD142⁺ population abundance and FAP adipogenesis, consistent with previous findings in adipose tissue. This supports the role of CD142⁺ cells as Aregs in skeletal muscle. Using our patent pending ParaTalk device, adipogenesis was maintained (measured by FABP4 immunofluorescence, Fig.1 D-F) when FAPs of normal-weight subjects were exposed to soluble stimuli secreted by Aregs from normal or obese subjects. In contrast, obese FAPs exhibited at least 100% increase in adipogenicity when exposed to secreted factors from either normal or obese Aregs. Cytokine profiling of Areg- and FAP-conditioned media revealed differential secretion patterns between obese and normal weight groups. Notably, Obese Aregs and FAPs exhibited increased secretion of Dickkopf 1 (Dkk1) and IGFBP-3, regulators of adipogenesis, while obese Aregs also upregulated pentraxin 3 and endoglin, factors linked to inflammation and adipogenesis in obesity.

Overall, these data support the presence of a local Areg population in skeletal muscle that regulates the adipogenicity of FAPs. We demonstrated that FAPs are more adipogenic in obese subjects and that obesity disrupts Areg-FAP paracrine signaling, shifting FAPs toward adipogenesis. Thus Areg secreted factors, which are dyregulated in obesity, could be therapeutic targets to mitigate intramuscular fatty accumulation.

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