Endocrine Abstracts

Background: Macrophages the key players in coordinating muscle regeneration in response to injury and damage, where androgens such as testosterone (T) and dihydrotestosterone (DHT) contribute to anabolic muscle metabolism. We have shown that androgen metabolism in macrophages is dynamically regulated by inflammation. We propose that this process may be dysregulated in inflammatory disease.

Methods: Primary human macrophages from healthy donors, were polarised (TNFα/IFNγ) or left unpolarised before treatment with DHT precursors (T & A4;100 nmol/l). Treated macrophages or conditioned media were then incubated or co-cultured with primary muscle myotube and myoblast cultures generated from healthy human quadriceps. Macrophage DHT synthesis was measured by LCMS. Muscle myotube thickness (microscopy), markers of muscle metabolism (qRT-PCR), cell migration (scratch assay), proliferation assay (BrdU), and protein synthesis (synthesis assay) were then assessed.

Results: Inflammatory-activated macrophages showed a unique regulation of steroid metabolism increasing DHT activation from T and A4. Conditioned media or co-culture of activated macrophages resulted in attenuated myotube fiber size without influencing the metabolic gene expression profile. Conditioned media with T increased proliferation after 48 hours (P = 0.0768) and 72 hours (P = 0.0738) treatment in myoblasts without changing cell viability. The conditioned media with T decreased catabolic Foxo1 and anti-anabolic Myostatin (Mstn) and increased differentiation marker Myodesmin gene expression after 24-hour treatment. In contrast, the addition of T to these inflammatory macrophages increased fiber thickness (P < 0.001, ***). DHT treatment did not increase the protein synthesis rate compared to control. Examination in myoblasts revealed that inflammatory macrophage-conditioned media increased cell migration and proliferation independently of T precursor treatment.

Conclusions: This study reveals that inflammatory-activated macrophages dynamically regulate androgen metabolism, and influence myotube thickness and metabolism. Whether this process is dysregulated in chronic inflammatory diseases resulting in a maladaptive response to muscle injury and regeneration has yet to be determined.