Integrin-β1/FAK signaling is involved in electrical stimulation to prevent disuse muscular atrophy induced by tail suspension in mice.

Effects of Electrical Muscle Stimulation on Skeletal Muscle During Lipopolysaccharide-Induced Inflammation: A Controlled Murine Study.

EMS applied during LPS-induced systemic inflammation exacerbated skeletal muscle atrophy and was associated with activation of IL-6/STAT3-C/EBPδ signaling and proteolytic pathways.

Aging preserves mTORC1 but attenuates JNK-SMAD2L signaling sensitivity to passive stretch-induced tension development in isolated mouse skeletal muscle.

INTRODUCTION Aging is associated with impaired skeletal muscle mass and function, often attributed to reduced sensitivity to anabolic stimuli. This study investigated whether aging influences the sensitivity of key anabolic signaling pathways to mechanical tension development in skeletal muscle. METHODS Using an ex vivo model, extensor digitorum longus (EDL) muscles from adult (16 weeks) and old (24 months) female mice were subjected to a standardized passive stretch protocol, with contralateral muscles serving as controls. During recovery, phosphorylation of proteins related to downstream mTORC1 and JNK-SMAD2-L signaling were assessed by immunoblotting. RESULTS Passive stretch significantly increased phosphorylation of mTORC1-related proteins (mTOR, p70S6K, rpS6, and 4E-BP1) in both adult and old muscles, with no significant differences between age groups, indicating preserved mTORC1 signaling sensitivity to mechanical tension with aging. In contrast, the magnitude of activation of JNK and SMAD2-L signaling was attenuated in old muscles. DISCUSSION Our findings reveal that mechanosensitive anabolic signaling is differentially affected by aging. While the intrinsic capacity for mTORC1 activation in response to mechanical tension appears to be preserved with aging, JNK-SMAD2L signaling exhibits reduced mechanosensitivity in aged muscle. This divergence suggests that aging selectively impairs tension-sensitive transcriptional pathways, potentially constraining muscle remodeling despite preserved translational signaling capacity. These findings further imply that age-related deficits observed in vivo may, at least in part, arise from systemic influences rather than intrinsic defects adhering to mTORC1 mechanotransduction.

The Integrin-Mediated Focal Adhesion Is Critically Involved in the Macrophage-to-Myofibroblast Transition in Subretinal Fibrosis.

Fibrosis, a common endpoint of chronic inflammatory diseases across organs, remains a major therapeutic challenge. Macrophages are central regulators of fibrotic remodeling, with evidence suggesting their direct role through macrophage-to-myofibroblast transition (MMT). However, the upstream mechanisms governing macrophage fibrogenic reprogramming remain unclear. Using a laser-induced mouse model of subretinal fibrosis, we investigated whether adhesion-dependent mechanotransduction regulates macrophage-driven fibrosis. Bulk RNA-seq of retinal pigment epithelium (RPE)-choroid tissues revealed significant enrichment of adhesion-related genes and focal adhesion pathways, with upregulation of integrins such as Itgb2, Itgal, and Itgax. Increased integrin expression and focal adhesion kinase phosphorylation (pFAK) were detected in infiltrating F4/80+ macrophages within fibrotic lesions. Bone marrow-derived macrophages under high-adherence conditions expressed higher levels of fibrosis-related genes and focal adhesion kinases-related genes such as Ptk2 and Ptk2b. FAK inhibitor PF562271 suppressed TGF-β1-induced upregulation of fibrosis-related genes (Col1a1, Fn1, Acta2) and α-SMA in macrophages. Intraperitoneal administration PF562271 reduced adhesion molecules ITGB2 and ITGAL expression on circulating monocytes and alleviated subretinal fibrosis. These findings identify integrin-FAK-mediated mechanotransduction as a key regulator of macrophage fibrogenic reprogramming and MMT, highlighting adhesion-dependent signaling as a conserved pathway linking tissue remodeling to fibrotic macrophage activation and FAK as a potential therapeutic target.

Biomechanical stiffness is essential for CD8+ T cell activation and proliferation 2258840

The cytoskeleton maintains cellular shape and structure, and serves as a biomechanical regulator of cellular responses. Although CD8+ T cell activation is well characterized, the roles of mechanotransduction and cytoskeletal stiffness remain unclear. Understanding how these biomechanical properties affect CD8+ T cell activation and function could provide new insight into immune regulation. We examined CD8+ T cells from a Protein Tyrosine Phosphatase Non-Receptor Type 21 knockout (Ptpn21⁻/⁻, KO) mouse model, previously reported to exhibit a disorganized actin cytoskeleton in hematopoietic stem cells. Intrinsic biomechanical properties were quantified using atomic force microscopy (AFM) with Hertzian modeling. Functional consequences of altered stiffness were evaluated by flow cytometry, comparing KO and wild-type (WT) mice after in vitro stimulation and in vivo adoptive transfer of CD8+OT-I T cells into B16-OVA tumor-bearing recipients. AFM revealed that Ptpn21⁻/⁻ CD8+ T cells were mechanically softer with a reduced elastic modulus. This softening was functionally significant to CD8+ T cell behavior. KO cells showed reduced activation upon CD3/CD28 bead stimulation, while responses to soluble OVA peptide remained comparable, indicating defective mechanotransduction. Calcium-flux assays demonstrated reduced store-operated Ca²+ entry, and AFM showed prolonged relaxation time, together suggesting impaired mechanotransduction during early TCR signaling. In vivo, the percentage of KO CD8+ T cells circulating in the spleen, lymph nodes, and peripheral blood was significantly lower than that of WT cells in a competitive adoptive transfer model, and the residual KO cells were less activated and proliferative. In conclusion, our findings demonstrate that cytoskeletal softening in Ptpn21⁻/⁻ CD8+ T cells impairs mechanotransduction, resulting in weakened T cell activation and reduced proliferation within a tumor-bearing environment. HL162725, HL130995, CA282579 Immune Response Regulation: Cellular Mechanisms (IRC)

Characterization of calcium sources and downstream signaling pathways following electrical field stimulation of rodent longitudinal esophageal muscle

Aims To explore the mechanisms involved in esophageal body longitudinal muscle contraction induced by electrical field stimulation. Methods Isometric contractions of esophageal segments from wistar rats in an organ bath were induced by electrical field stimulation (duration 1 s, frequency 1-100 Hz, intensity 30-90 V) before and after application of pharmacological probes to test involvement of muscarinic receptors, Rho kinase, Ca2+ release, protein kinase C, calmodulin and L-type Ca2+ channels. Results Electrical field stimulation (EFS) induced contractions showed a frequency and intensity-dependent behavior. Based on the effect size, expressed by the Cohen’s d, they were insensitive to the muscarinic receptor blocker atropine (1 µM), the Rho kinase inhibitor Y-27632 (10 µM) as well as the inhibitors of Ca2+ release 2-aminoethoxydiphenylborane (2-APB, 100µM) and 1,1’-diheptyl-4,4’-bipyridinium (DHBP, 100 µM). In contrast, contractions were reduced by the protein kinase C inhibitor chelerythrine (10µM) and by the calmodulin antagonist N-[6-aminohexyl]-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7, 100 µM). Verapamil (100 µM) abolished EFS-induced contractions. Conclusions Based on our findings with 2-APB, DHBP, and verapamil, extracellular Ca²+ appears to be the source of the increase in intracellular Ca²+ underlying EFS-induced EB contractions. Furthermore, the effects observed with chelerythrine and W-7 may suggest that this increase in intracellular Ca²+ may subsequently activate PKC- and calmodulin-dependent signaling pathways.

Cardiomyocyte-specific depletion of integrin α3 preserves cardiac function after myocardial infarction