Improved health by combining dietary restriction and promoting muscle growth in DNA repair-deficient progeroid mice

DR temporarily suppresses growth, and when applied to progeroid DNA repair-deficient mice doubles lifespan with systemic health benefits. Counterintuitively, attenuation of myostatin/activin signalling by soluble activin receptor (sActRIIB), boosts the growth of muscle, and in these animals prevents muscle wasting, improves kidney functioning, and compresses morbidity. Here we investigated a combined approach, applying an anabolic regime (sActRIIB) at the same time as DR to Ercc1d/- progeroid mice. Following both single treatments and combined, we monitored global effects on body weight, lifespan and behaviour, and local effects on muscle and tissue weight, muscle morphology and function, and ultrastructural and transcriptomic changes in muscle and kidney. Lifespan was mostly influenced by DR (extended from approx. 20 to 40-weeks; p<0.001), with sActRIIB clearly increasing muscle mass (35-65%) and tetanic force (p<0.001). The combined regime yielded a stable uniform body weight, but increased compared to DR alone, synergistically improved motor coordination and further delayed the onset and development of balance problems. sActRIIB significantly increased muscle fibre size (p<0.05) in mice subjected to DR and lowered all signs of muscle damage. In the neuromuscular junction of Ercc1d/- mice the junctional folding of the basement membrane at the postsynaptic side was either rudimentary or completely missing. Single interventions by sActRIIB treatment or DR only partially rescued this phenotype, while in the double intervention group the regularly shaped junctional foldings were maintained. In kidney of Ercc1d/- mice we observed a mild but significant foot process effacement, which was restored by either intervention. Transcriptome analysis also pointed towards reduced levels of DNA damage in muscle and kidney by DR, but not sActRIIB, while these levels retained lower in the double intervention. In muscle we found synergistic effects of combining sActRIIB with DR, but not in kidney, with an overall better health in the double intervention group. Crucially, the benefits of each single intervention are not lost when administered in combination, but rather strengthened, even when sActRIIB was applied late in life, opening opportunities for translation to human.