Loss of sarcospan exacerbates pathology inmdxmice, but does not affect utrophin amelioration of disease

Abstract

The dystrophin–glycoprotein complex (DGC) is a membrane adhesion complex that provides structural stability at the sarcolemma by linking the myocyte’s internal cytoskeleton and external extracellular matrix. In Duchenne muscular dystrophy (DMD), the absence of dystrophin leads to the loss of the DGC at the sarcolemma, resulting in sarcolemmal instability and progressive muscle damage. Utrophin (UTRN), an autosomal homolog of dystrophin, is upregulated in dystrophic muscle and partially compensates for the loss of dystrophin in muscle from patients with DMD. Here, we examine the interaction between Utr and sarcospan (SSPN), a small transmembrane protein that is a core component of both UTRN–glycoprotein complex (UGC) and DGC. We show that additional loss of SSPN causes an earlier onset of disease in dystrophin-deficient mdx mice by reducing the expression of the UGC at the sarcolemma. In order to further evaluate the role of SSPN in maintaining therapeutic levels of Utr at the sarcolemma, we tested the effect of Utr transgenic overexpression in mdx mice lacking SSPN (mdx:SSPN −/−:Utr-Tg). We found that overexpression of Utr restored SSPN to the sarcolemma in mdx muscle but that the ablation of SSPN in mdx muscle reduced Utr at the membrane. Nevertheless, Utr overexpression reduced central nucleation and improved grip strength in both lines. These findings demonstrate that high levels of Utr transgenic overexpression ameliorate the mdx phenotype independently of SSPN expression but that loss of SSPN may impair Utr-based mechanisms that rely on lower levels of Utr protein.

Promising therapeutic approaches of utrophin replacing dystrophin in the treatment of Duchenne muscular dystrophy

“…The knockout of SSPN of mdx mice increases utrophin and related DG proteins in the endoplasmic reticulum and Golgi apparatus. However, the transport of these sarcolemma-related proteins to the sarcolemma is hindered [58] . The absence of DPC-related proteins can cause limb-girdle muscular dystrophy and dystroglycanopathy.…”

Sarcospan Deficiency Increases Oxidative Stress and Arrhythmias in Hearts after Acute Ischemia-Reperfusion Injury

“…The protein SSPN has been shown to be important in maintaining cardiac and skeletal muscle function and integrity [8,9]. Unlike the other DGC subunits, it remains unclear whether SSPN has a role in pathogenesis.…”