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ZAKb is a cellular compression sensor that mediates hypertrophic signaling in skeletal muscle

ABSTRACT: Mechanosensing is required for the senses of touch and hearing, and impacts on cellular processes such as cell differentiation, migration, invasion and tissue homeostasis. Mechanical inputs give rise to p38- and JNK-signaling, which mediates adaptive physiological responses in various tissues. In muscle, fiber contraction-induced p38 and JNK signaling ensures adaptation to exercise, muscle repair and hypertrophy. However, the mechanism by which muscle fibers sense mechanical load to activate this signaling, as well as the physiological roles of mechanical stress sensing more broadly, have remained elusive. Here, we show that the upstream MAP3K ZAK is a sensor of cellular compression induced by osmotic shock and cyclic compression in vitro, and muscle contraction in vivo. This function relies on ZAK’s ability to recognize stress fibers in cells and the corresponding Z-discs in muscle fibers, when under tension. Consequently, ZAK-deficient mice present with skeletal muscle defects characterized by fibers with centralized nuclei and progressive adaptation towards a slower myosin profile. Our results highlight how cells in general sense mechanical compressive load, and how mechanical forces generated during muscle contraction are translated into MAP kinase signaling.

INSTRUMENT(S): Orbitrap Exploris 480

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Thigh Muscle

SUBMITTER: Ana Martinez-Val

LAB HEAD: Jesper V. Olsen

PROVIDER: PXD028548 | Pride | 2022-05-31

REPOSITORIES: Pride

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Project description:Background: Niemann-Pick disease type A (NPDA), a disease caused by mutations in acid sphingomyelinase (ASM), involves severe neurodegeneration and early death. Intracellular lipid accumulation and plasma membrane alterations are implicated in the pathology. ASM is also linked to the mechanism of plasma membrane repair, so we investigated the impact of ASM deficiency in skeletal muscle, a tissue that undergoes frequent cycles of injury and repair in vivo. Methods: Utilizing the NPDA/B mouse model ASM−/− and wild type (WT) littermates, we performed excitation- contraction coupling/Ca2+ mobilization and sarcolemma injury/repair assays with isolated flexor digitorum brevis fibers, proteomic analyses with quadriceps femoris, flexor digitorum brevis, and tibialis posterior muscle and in vivo tests of the contractile force (maximal isometric torque) of the quadriceps femoris muscle before and after eccentric contraction-induced muscle injury. Results: ASM−/− flexor digitorum brevis fibers showed impaired excitation-contraction coupling compared to WT, a defect expressed as reduced tetanic [Ca2+]i in response to electrical stimulation and early failure in sustaining [Ca2+]i during repeated tetanic contractions. When injured mechanically by needle passage, ASM−/− flexor digitorum brevis fibers showed susceptibility to injury similar to WT, but a reduced ability to reseal the sarcolemma. Proteomic analyses revealed changes in a small group of skeletal muscle proteins as a consequence of ASM deficiency, with downregulation of calsequestrin occurring in the three different muscles analyzed. In vivo, the loss in maximal isometric torque of WT quadriceps femoris was similar immediately after and 2 min after injury. The loss in ASM−/− mice immediately after injury was similar to WT, but was markedly larger at 2 min after injury. Conclusions: Skeletal muscle fibers from ASM−/− mice have an impairment in intracellular Ca2+ handling that results in reduced Ca2+ mobilization and a more rapid decline in peak Ca2+ transients during repeated contraction-relaxation cycles. Isolated fibers show reduced ability to repair damage to the sarcolemma, and this is associated with an exaggerated deficit in force during recovery from an in vivo eccentric contraction- induced muscle injury. Our findings uncover the possibility that skeletal muscle functional defects may play a role in the pathology of NPDA/B disease.

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ZAKb is a cellular compression sensor that mediates hypertrophic signaling in skeletal muscle

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