Hord Jeffrey M, Burns Sarah, Willer Tobias, Goddeeris Matthew M, Venzke David, Campbell Kevin P
Department of Molecular Physiology and Biophysics, and Department of Neurology, Howard Hughes Medical Institute, Senator Paul D. Wellstone Muscular Dystrophy Specialized Research Center, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, Iowa, USA.
Skelet Muscle. 2025 Jan 9;15(1):1. doi: 10.1186/s13395-024-00370-2.
Maintaining the connection between skeletal muscle fibers and the surrounding basement membrane is essential for muscle function. Dystroglycan (DG) serves as a basement membrane extracellular matrix (ECM) receptor in many cells, and is also expressed in the outward-facing membrane, or sarcolemma, of skeletal muscle fibers. DG is a transmembrane protein comprised of two subunits: alpha-DG (α-DG), which resides in the peripheral membrane, and beta-DG (β-DG), which spans the membrane to intracellular regions. Extensive post-translational processing and O-mannosylation are required for α-DG to bind ECM proteins, which is mediated by a glycan structure known as matriglycan. O-mannose glycan biosynthesis is initiated by the protein O-mannosyltransferase 1 (POMT1) and POMT2 enzyme complex and leads to three subtypes of glycans called core M1, M2, and M3. The lengthy core M3 is capped with matriglycan. Genetic defects in post-translational O-mannosylation of DG interfere with its receptor function and result in muscular dystrophy with central nervous system and skeletal muscle pathophysiology.
To evaluate how the loss of O-mannosylated DG in skeletal muscle affects the development and progression of myopathology, we generated and characterized mice in which the Pomt1 gene was specifically deleted in skeletal muscle (Pomt1) to interfere with POMT1/2 enzyme activity. To investigate whether matriglycan is the primary core M glycan structure that provides the stabilizing link between the sarcolemma and ECM, we generated mice that retained cores M1, M2, and M3, but lacked matriglycan (conditional deletion of like-acetylglucosaminyltransferase 1; Large1). Next, we restored Pomt1 using gene transfer via AAV2/9-MCK-mPOMT1 and determined the effect on Pomt1 pathophysiology.
Our data showed that in Pomt1 mice O-mannosylated DG is required for sarcolemma resilience, remodeling of muscle fibers and muscle tissue, and neuromuscular function. Notably, we observed similar body size limitations, sarcolemma weakness, and neuromuscular weakness in Large1 mice that only lacked matriglycan. Furthermore, our data indicate that genetic rescue of Pomt1 in Pomt1 mice limits contraction-induced sarcolemma damage and skeletal muscle pathology.
Collectively, our data indicate that DG modification by Pomt1/2 results in core M3 capped with matriglycan, and that this is required to reinforce the sarcolemma and enable skeletal muscle health and neuromuscular strength.
维持骨骼肌纤维与周围基底膜之间的连接对于肌肉功能至关重要。在许多细胞中，肌营养不良蛋白聚糖（DG）作为基底膜细胞外基质（ECM）受体，也在骨骼肌纤维向外的膜（即肌膜）中表达。DG是一种跨膜蛋白，由两个亚基组成：位于外周膜的α-肌营养不良蛋白聚糖（α-DG）和跨膜至细胞内区域的β-肌营养不良蛋白聚糖（β-DG）。α-DG与ECM蛋白结合需要广泛的翻译后加工和O-甘露糖基化，这由一种称为基质糖链的聚糖结构介导。O-甘露糖聚糖生物合成由蛋白质O-甘露糖基转移酶1（POMT1）和POMT2酶复合物启动，并产生三种聚糖亚型，称为核心M1、M2和M3。冗长的核心M3被基质糖链封端。DG翻译后O-甘露糖基化的遗传缺陷会干扰其受体功能，并导致伴有中枢神经系统和骨骼肌病理生理学的肌肉营养不良。
为了评估骨骼肌中O-甘露糖基化DG的缺失如何影响肌病的发展和进展，我们构建并鉴定了在骨骼肌中特异性缺失Pomt1基因（Pomt1）以干扰POMT1/2酶活性的小鼠。为了研究基质糖链是否是在肌膜和ECM之间提供稳定连接的主要核心M聚糖结构，我们构建了保留核心M1、M2和M3但缺乏基质糖链的小鼠（条件性缺失类乙酰葡糖胺基转移酶1；Large1）。接下来，我们通过AAV2/9-MCK-mPOMT1基因转移恢复Pomt1，并确定其对Pomt病理生理学的影响。
我们的数据表明，在Pomt1小鼠中，O-甘露糖基化DG对于肌膜弹性、肌纤维和肌肉组织重塑以及神经肌肉功能是必需的。值得注意的是，我们在仅缺乏基质糖链的Large1小鼠中观察到了类似的体型限制、肌膜无力和神经肌肉无力。此外，我们的数据表明，Pomt1小鼠中Pomt1的基因拯救限制了收缩诱导的肌膜损伤和骨骼肌病理。
总体而言，我们的数据表明，Pomt1/2对DG的修饰导致核心M3被基质糖链封端，这是加强肌膜并实现骨骼肌健康和神经肌肉力量所必需的。
