Elevated CD47 is a hallmark of dysfunctional aged muscle stem cells that can be targeted to augment regeneration

In aging, skeletal muscle strength and regenerative capacity decline, due in part to functional impairment of muscle stem cells (MuSCs), yet the underlying mechanisms remain elusive. Here, we capitalize on mass cytometry to identify high CD47 expression as a hallmark of dysfunctional MuSCs (CD47hi) with impaired regenerative capacity that predominate with aging. The prevalent CD47hi MuSC subset suppresses the residual functional CD47lo MuSC subset through a paracrine signaling loop, leading to impaired proliferation. We uncover that elevated CD47 levels on aged MuSCs result from increased U1 snRNA expression, which disrupts alternative polyadenylation. The deficit in aged MuSC function in regeneration can be overcome either by morpholino-mediated blockade of CD47 alternative polyadenylation or antibody blockade of thrombospondin-1/CD47 signaling, leading to improved regeneration in aged mice, with therapeutic implications. Our findings highlight a previously unrecognized age-dependent alteration in CD47 levels and function in MuSCs, which underlies reduced muscle repair in aging.

Abstract P2120: Microdystrophin Design Comparisons In Dystrophin-Deficient Cardiomyocytes

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease caused by the lack of dystrophin. Dilated cardiomyopathy is the leading cause of death in DMD patients. Preclinical data show that smaller versions of dystrophin, called microdystrophins, can ameliorate disease progression. These transgenes, amenable to packaging into adeno-associated virus, have shown to be effective in improving skeletal muscle function; however, the functional benefit of microdystrophins in delaying heart failure is unknown. To identify the design principles that are important for addressing DMD heart dysfunction, three microdystrophin variants currently in clinical trials were tested in cardiomyocytes differentiated from induced pluripotent stem cells (iPSC-CMs) with deficiencies in dystrophin. Previously, we reported that mechanical contraction and calcium handling are impaired in DMD iPSC-CMs. To test the functional benefit of the microdystrophins, we performed traction force microscopy, that provides multiparametric measurements of contraction, and calcium imaging with a ratiometric calcium-binding dye. Our results show a partial rescue of contractile deficits and aberrant calcium handling, underscoring the need for new design variants that address cardiomyocyte dysfunction.