Murine obscurin and Obsl1 have functionally redundant roles in sarcolemmal integrity, sarcoplasmic reticulum organization, and muscle metabolism

Abstract

Biological roles of obscurin and its close homolog Obsl1 (obscurin-like 1) have been enigmatic. While obscurin is highly expressed in striated muscles, Obsl1 is found ubiquitously. Accordingly, obscurin mutations have been linked to myopathies, whereas mutations in Obsl1 result in 3M-growth syndrome. To further study unique and redundant functions of these closely related proteins, we generated and characterized Obsl1 knockouts. Global Obsl1 knockouts are embryonically lethal. In contrast, skeletal muscle-specific Obsl1 knockouts show a benign phenotype similar to obscurin knockouts. Only deletion of both proteins and removal of their functional redundancy revealed their roles for sarcolemmal stability and sarcoplasmic reticulum organization. To gain unbiased insights into changes to the muscle proteome, we analyzed tibialis anterior and soleus muscles by mass spectrometry, uncovering additional changes to the muscle metabolism. Our analyses suggest that all obscurin protein family members play functions for muscle membrane systems.

The Role of Cullin-RING Ligases in Striated Muscle Development, Function, and Disease

“…Generation and culture of Obsl1 knockout lung fibroblasts are described elsewhere [ 372 ]. Isolation and culture of neonatal mouse cardiomyocytes (NMCs) was done as previously described [ 381 ].…”

“…All procedures involving vertebrate animals were reviewed and approved by the Animal Care and Use Committee at the University of California San Diego (protocol number S13009, approval date 12/19/2019). Skeletal muscle specific obscurin and Obsl1 knockout mice were described previously [ 372 ].…”

“…In cross-striated muscles, both obscurin and Obsl1 are co-expressed and were shown to play important roles in maintaining muscle structure by binding redundantly to the sarcomeric proteins titin and myomesin [ 343 , 344 ]. Removal of both obscurin and Obsl1 affected sarcolemmal integrity, sarcoplasmic reticulum organization (including sAnk1.5 protein levels), and metabolism of skeletal muscles [ 372 , 373 , 374 , 375 ]. However, the reduction of cullin E3-ligase levels in tibialis anterior muscles is less noticeable compared to knockout lung fibroblasts ( Figure 7 F).…”

miR-486 is modulated by stretch and increases ventricular growth

“…Immunoblots of SDS-acrylamide gels or SDS-agarose gels were performed as previously described (77, 78). Briefly, protein samples lysed into sample buffer were boiled for 2 minutes and loaded onto 4%–20% polyacrylamide gradient gels (Bio-Rad) or SDS-agarose gels.…”

Exploring Obscurin and SPEG Kinase Biology

“…Surprisingly though, unlike SPEG knockouts, loss of obscurin in mice is tolerable [ 35 ], suggesting that loss of function can be compensated during cardiac development. Part of the explanation may be due to overlapping functions between obscurin and other members of this protein family [ 36 ]. More recently, a new mouse model was established that sheds further light on the biological functions of obscurin: mice that delete Ig-domains 58/59 of the protein display age-dependent pathological remodeling of the heart and arrhythmias [ 37 ].…”