Yuri Yamashita

This study reveals that perlecan, a basement membrane proteoglycan, regulates exercise-induced vascular adaptations and isoform-specific expression of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α) in skeletal muscle. Perlecan-deficient muscle exhibited enhanced levels of alternative promoter-driven PGC-1α isoforms, upregulation of angiogenic genes following acute exercise, and increased baseline and exercise-induced capillary density. These findings demonstrate that basement membrane extracellular matrix composition is associated with exercise-induced muscle-vascular cross talk, identifying perlecan as a candidate regulator of exercise training adaptations.

The extracellular matrix (ECM) of the brain undergoes dynamic remodeling during development and is crucial for neuronal plasticity. While chondroitin sulfates (CS) regulate oligodendrocyte differentiation and myelination, their relationship with oligodendrocyte precursors (OPCs) and synaptic plasticity remains unclear. This study investigated a novel CS‐rich ECM structure, its origin, and its role in synaptic plasticity. Using immunohistochemistry, disaccharide analysis, and dendritic spine characterization in mice, we examined postnatal development and analyzed single‐cell RNA (scRNA) sequencing data from the National Center for Biotechnology Information database. We identified patch‐like structures labeled with the chondroitin sulfate 56 (CS56) antibody (CS clusters) distinct from Wisteria floribunda agglutinin‐positive perineuronal nets. Oligodendrocyte lineage cells expressing G protein‐coupled receptor 17 (GPR17) localized at CS cluster centers, emerging postnatally and peaking at day 14, preceded CS cluster formation. ScRNA sequencing of Gpr17 + cells revealed the expression of carbohydrate sulfotransferase 3 ( Chst3 ) and uronyl 2‐sulfotransferase ( Ust ), genes coding enzymes synthesizing type C and D CS disaccharides, the primary components of the CS56 antibody epitope. Disaccharide analysis revealed elevated levels of type D chondroitin sulfate at day 35. Notably, dendritic spines within the CS clusters were longer and larger than those outside these regions, suggesting enhanced synaptic connectivity. Our findings reveal a CS‐rich structure in the brain ECM that is causally linked to GPR17+ oligodendrocyte lineage cells and closely related to neuronal circuit development. The morphological differences in dendritic spines within CS clusters and persistence of GPR17+ oligodendrocyte lineage cells beyond the postnatal period suggest additional functions that warrant further investigation.

Heparan sulfate proteoglycans (HSPGs) are extracellular matrix components that play central roles in skeletal muscle development, maintenance, and regeneration. HSPGs are localized to the basement membrane, sarcolemma, neuromuscular junction, and satellite cell niche, where they exert multifaceted functions, including providing structural stability, storing and releasing growth factors, and controlling mechanotransduction. Throughout each stage from muscle development to maturation, the expression levels of HSPGs and modification patterns of HS chains change dynamically, precisely controlling myogenesis. Changes in HS sulfation patterns regulate growth factor signaling and affect muscle cell proliferation and differentiation. Based on mechanotransduction control mechanisms elucidated through our perlecan research, this review demonstrates that mechanotransduction control by HSPGs constitutes an important molecular basis for muscle mass and metabolic regulation. HSPG abnormalities are associated with muscular dystrophy, sarcopenia, and metabolic diseases, making the development of therapeutic strategies targeting HSPGs and HS chains a promising area of research.

ヘパラン硫酸プロテオグリカン（HSPG）は、骨格筋の発生・維持・再生において中心的役割を担う細胞外マトリックス構成成分である。HSPGは基底膜、筋細胞膜、神経筋接合部、衛星細胞ニッチに局在し、構造安定性の提供、成長因子の貯蔵・放出、メカノトランスダクションの制御など多面的機能を発揮する。筋発生から成熟に至る各段階で、HSPGの発現量とHS鎖の修飾パターンが動的に変化し、筋形成を精密に制御している。HSの硫酸化パターンの変化は、成長因子シグナル伝達を調節し、筋細胞の増殖・分化に影響を与える。我々のパールカン研究から見出されたメカノトランスダクション制御機構に基づいて、HSPGによるメカノトランスダクション制御が筋量・代謝制御の重要な分子基盤であることを示す。HSPG異常は筋ジストロフィー、サルコペニア、代謝性疾患と関連し、HSPGまたはHS鎖を標的とした治療戦略の開発が期待される。

Schwartz–Jampel syndrome (SJS) is an autosomal recessive disorder caused by loss-of-function mutations in heparan sulfate proteoglycan 2 (HSPG2), which encodes the core basement membrane protein perlecan. Myotonia is a major criterion for the diagnosis of SJS; however, its evaluation is based solely on physical examination and can be challenging in neonates and young children. Furthermore, the pathomechanism underlying SJS-related myotonia is not fully understood, and effective treatments for SJS are limited. Here, we established a cellular model of SJS using patient-derived human-induced pluripotent stem cells. This model exhibited hyper-responsiveness to acetylcholine as a result of abnormalities in the perlecan molecule, which were confirmed via comparison of their calcium imaging with calcium imaging of satellite cells derived from Hspg2^−/−-Tg mice, which exhibit myotonic symptoms similar to SJS symptoms. Therefore, our results confirm the utility of creating cellular models for investigating SJS and their application in evaluating myotonia in clinical cases, while also providing a useful tool for the future screening of SJS therapies.

In skeletal muscles, muscle fibers are highly organized and bundled within the basement membrane. Several microfabricated substrate models have failed to mimic the macrostructure of native muscle, including various extracellular matrix (ECM) proteins. Therefore, we developed and evaluated a system using decellularized muscle tissue and mouse myoblasts C2C12 to analyze the interaction between native ECM and myocytes. Chicken skeletal muscle was sliced into sheets and decellularized to prepare decellularized skeletal muscle sheets (DSMS). C2C12 was then seeded and differentiated on DSMS. Immunostaining for ECM molecules was performed to examine the relationship between myoblast adhesion status, myotube orientation, and collagen IV orientation. Myotube survival in long-term culture was confirmed by calcein staining. C2C12 myoblasts adhered to scaffolds in DSMS and developed adhesion plaques and filopodia. Furthermore, C2C12 myotubes showed orientation along the ECM orientation within DSMS. Compared to plastic dishes, detachment was less likely to occur on DSMS, and long-term incubation was possible. This culture technique reproduces a cell culture environment reflecting the properties of living skeletal muscle, thereby allowing studies on the interaction between the ECM and myocytes.

Perlecan is an extracellular matrix molecule anchored to the sarcolemma by a dystrophin–glycoprotein complex. Perlecan-deficient mice are tolerant to muscle atrophy, suggesting that perlecan negatively regulates mechanical stress-dependent skeletal muscle mass. Delocalization of neuronal nitric oxide synthase (nNOS) from the sarcolemma to the cytosol triggers protein degradation, thereby initiating skeletal muscle atrophy. We hypothesized that perlecan regulates nNOS delocalization and activates protein degradation during this process. To determine the role of perlecan in nNOS-mediated mechanotransduction, we used sciatic nerve transection as a denervation model of gastrocnemius muscles. Gastrocnemius muscle atrophy was significantly lower in perinatal lethality-rescued perlecan-knockout (Hspg2^−/−-Tg) mice than controls (WT-Tg) on days 4 and 14 following surgery. Immunofluorescence microscopy showed that cell membrane nNOS expression was reduced by denervation in WT-Tg mice, with marginal effects in Hspg2^−/−-Tg mice. Moreover, levels of atrophy-related proteins—i.e., FoxO1a, FoxO3a, atrogin-1, and Lys48-polyubiquitinated proteins—increased in the denervated muscles of WT-Tg mice but not in Hspg2^−/−-Tg mice. These findings suggest that during denervation, perlecan promotes nNOS delocalization from the membrane and stimulates protein degradation and muscle atrophy by activating FoxO signaling and the ubiquitin–proteasome system.