Downregulation of Organ-Derived Activin A Attenuates Muscle Atrophy and Intramuscular Fat Infiltration in Cancer Cachexia Mice.

Abstract

BACKGROUND: Cancer cachexia is a multifactorial wasting syndrome marked by profound skeletal muscle loss. Tumours can release high levels of Activin A (ActA), which activates the ubiquitin-proteasome pathway (UPP) and drives muscle wasting. Systemic blockade of the ActA pathway is associated with inflammatory adverse effects, and tumour-restricted targeting alone often fails to reverse cachexia. We asked whether ActA produced by host (nontumour) organs contributes to circulating ActA and muscle wasting. METHODS: We profiled ActA across tissues and in serum in Lewis lung carcinoma (LLC) cancer cachexia mice to generate an organ-wide expression map. Functional studies were then performed using adeno-associated-virus (AAV)-knockdown in the heart (cTnT/hTCF21 promoters) and kidney (CMV promoter), followed by cachexia induction. Body weight (BW), food intake, skeletal muscle mass, muscle function and muscle histomorphology were assessed. Mitochondrial ultrastructure and lipid metabolic pathways in muscle and adipose tissue were also examined. RESULTS: LLC cachexia mice exhibited significant reductions in body weight (-6.0%, p&#x2009;<&#x2009;0.05), food intake (-9.9%, p&#x2009;<&#x2009;0.05), quadriceps mass (-15.3%, p&#x2009;<&#x2009;0.05) and grip strength (-13.0%, p&#x2009;<&#x2009;0.0001) compared with non-tumour-bearing (NTB) mice (n&#x2009;=&#x2009;6-12/group). ActA expression was markedly increased in the host organs, particularly in the kidney (2.8-fold vs. NTB, p&#x2009;<&#x2009;0.001) and heart (2.7-fold vs. NTB, p&#x2009;<&#x2009;0.05) (n&#x2009;=&#x2009;10/group). Compared with the sh-NC, organ-targeted ActA knockdown restored body weight (+6.1%, p&#x2009;<&#x2009;0.05) and food intake (+8.4%, p&#x2009;<&#x2009;0.05), increased quadriceps mass (+17.2%, p&#x2009;<&#x2009;0.05) and grip strength (+10.7%, p&#x2009;<&#x2009;0.01), reduced intramuscular fat infiltration and attenuated UPP signalling (n&#x2009;=&#x2009;8-16/group). These effects were accompanied by increased expression of the mitochondrial fatty-acid oxidation regulator carnitine palmitoyltransferase 1B (CPT1B) (+42.3% of mRNA level; +30.9% of protein level; both p&#x2009;<&#x2009;0.05) and CPT2 (+57.7% of mRNA level, p&#x2009;<&#x2009;0.05), improved mitochondrial ultrastructure and partial restoration of adipose mass. CONCLUSIONS: Simultaneous downregulation of Activin A in the kidney and heart attenuates skeletal muscle atrophy and intramuscular adipogenesis, improves muscle mass and function and mitigates adipose tissue mass loss in cancer cachexia mice. These findings identify heart- and kidney-derived Activin A as a key driver of cachexia, which acts through a combinatorial effect rather than an isolated contribution from either one alone, highlighting its potential as a therapeutic target.