Vinculin functions as a molecular clutch that organizes leading edge F-actin, generates traction, and promotes focal adhesion formation and turnover but not adhesion growth.

Vinculin is a ubiquitously expressed multiliganded protein that links the actin cytoskeleton to the cell membrane. In myocytes, it is localized in protein complexes which anchor the contractile apparatus to the sarcolemma. Its function in the myocardium remains poorly understood. Therefore, we developed a mouse model with cardiac-myocyte-specific inactivation of the vinculin (Vcl) gene by using Cre-loxP technology. Sudden death was found in 49% of the knockout (cVclKO) mice younger than 3 months of age despite preservation of contractile function. Conscious telemetry documented ventricular tachycardia as the cause of sudden death, while defective myocardial conduction was detected by optical mapping. cVclKO mice that survived through the vulnerable period of sudden death developed dilated cardiomyopathy and died before 6 months of age. Prior to the onset of cardiac dysfunction, ultrastructural analysis of cVclKO heart tissue showed abnormal adherens junctions with dissolution of the intercalated disc structure, expression of the junctional proteins cadherin and ␤1D integrin were reduced, and the gap junction protein connexin 43 was mislocalized to the lateral myocyte border. This is the first report of tissue-specific inactivation of the Vcl gene and shows that it is required for preservation of normal cell-cell and cell-matrix adhesive structures.

Vinculin and its muscle splice variant metavinculin link focal adhesions and cell-to-cell contact sites to the actin cytoskeleton. We hypothesized that normal expression of vinculin isoforms would be essential for integrity of cardiomyocytes and preservation of normal cardiac function. We studied heterozygous vinculin knockout mice (Vin؉/؊) that develop and breed normally. The Vin؉/؊ mice displayed: 1) a 58% reduction of vinculin and a 63% reduction of metavinculin protein levels versus wild-type littermates; 2) normal basal cardiac function and histology but abnormal electrocardiograms, intercalated disks, and ICD-related protein distribution; 3) increased mortality following acute hemodynamic stress imposed by transverse aortic constriction (TAC); 4) cardiac dysfunction by 6 weeks post-TAC; and 5) misalignment of ␣-actinin containing Z-lines and abnormal myocardial ultrastructure despite preserved cardiac function. Decreased expression of vinculin/metavinculin leads to abnormal myocyte structure without baseline physiological evidence of cardiac dysfunction. These structural changes predispose to stress-induced cardiomyopathy. Vinculin (Vin) is a 117-kd ubiquitously expressed, membrane-associated protein that links focal adhesions (cellsubstrate contacts), adherens junctions (cell-to-cell contacts), and costameres (subsarcolemmal adhesion plaques) to the actin cytoskeleton.1-3 This linkage occurs since vinculin binds to F-actin, ␣-actinin, ␣-catenin, and talin. 4 -6 In cardiac myocytes, vinculin is detected at the lateral sarcolemma, in transverse ribs called costameres, in Z-lines, as well as at cellular attachment sites termed intercalated disks (ICDs). 7-9Dilated cardiomyopathy has been associated with mutations in a number of structural proteins, and many such studies have shown that the link from sarcomere to cell membrane is critical for preservation of normal myocardial function and integrity. 10 Relevant to the focus of the current examination is that a 124-kd splice-variant isoform of vinculin, termed metavinculin (Mvin), is expressed only in cardiac and smooth muscle.11 Alterations in metavinculin have been recently related to human cardiomyopathy. 12,13 Homozygous inactivation of the murine vinculin gene caused embryonic lethality by E10.5. The embryos displayed a thin-walled myocardium and cerebral abnormalities including incomplete fusion of the neural folds.14 The heterozygous knockout mice (Vinϩ/Ϫ) develop and breed normally and are the focus of the current study. We hypothesized that reduced expression of vinculin/metavinculin in the intact Vinϩ/Ϫ mouse heart would lead to impaired cardiac function either in the basal condition or following hemodynamic stress. The strategy used to inactivate the vinculin gene in these mice leads to impaired production of vinculin as well as metavinculin.14 We found that the Vinϩ/Ϫ mice displayed: 1) a 58% reduction of vinculin and a 63% reduction of metavinculin protein levels versus wild-type littermates; 2) normal basal cardiac function and histology but abn...

Vinculin (Vcl) links actin filaments to integrin-and cadherin-based cellular junctions. Zonula occludens-1 (ZO-1, also known as TJP1) binds connexin-43 (Cx43, also known as GJA1), cadherin and actin. Vcl and ZO-1 anchor the actin cytoskeleton to the sarcolemma. Given that loss of Vcl from cardiomyocytes causes maldistribution of Cx43 and predisposes cardiomyocyte-specific Vcl-knockout mice with preserved heart function to arrhythmia and sudden death, we hypothesized that Vcl and ZO-1 interact and that loss of this interaction destabilizes gap junctions. We found that Vcl, Cx43 and ZO-1 colocalized at the intercalated disc. Loss of cardiomyocyte Vcl caused parallel loss of ZO-1 from intercalated dics. Vcl coimmunoprecipitated Cx43 and ZO-1, and directly bound ZO-1 in yeast two-hybrid studies. Excision of the Vcl gene in neonatal mouse cardiomyocytes caused a reduction in the amount of Vcl mRNA transcript and protein expression leading to (1) decreased protein expression of Cx43, ZO-1, talin, and b1D-integrin, (2) reduced PI3K activation, (3) increased activation of Akt, Erk1 and Erk2, and (4) cardiomyocyte necrosis. In summary, this is the first study showing a direct interaction between Vcl and ZO-1 and illustrates how Vcl plays a crucial role in stabilizing gap junctions and myocyte integrity.

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Interventions that preserve motor neurons or restore functional motor neuroplasticity may extend longevity in amyotrophic lateral sclerosis (ALS). Delivery of neurotrophins may potentially revive degenerating motor neurons, yet this approach is dependent on the proper subcellular localization of neurotrophin receptor (NTR) to plasmalemmal signaling microdomains, termed membrane/lipid rafts (MLRs). We previously showed that over‐expression of synapsin‐driven caveolin‐1 (Cav‐1) (SynCav1) increases MLR localization of NTR [e.g., receptor tyrosine kinase B (TrkB)], promotes hippocampal synaptic and neuroplasticity, and significantly improves learning and memory in aged mice. The present study crossed a SynCav1 transgene‐positive (SynCav1+) mouse with the mutant human superoxide dismutase glycine to alanine point mutation at amino acid 93 (hSOD1G93A) mouse model of ALS. When compared with hSOD1G93A, hSOD1G93A/SynCav1+ mice exhibited greater body weight and longer survival as well as better motor function. Microscopic analyses of hSOD1G93A/SynCav1+ spinal cords revealed preserved spinal cord α‐motor neurons and preserved mitochondrial morphology. Moreover, hSOD1G93A/SynCav1+ spinal cords contained more MLRs (cholera toxin subunit B positive) and MLR‐associated TrkB and Cav‐1 protein expression. These findings demonstrate that SynCav1 delays disease progression in a mouse model of ALS, potentially by preserving or restoring NTR expression and localization to MLRs.—Sawada, A., Wang, S., Jian, M., Leem, J., Wackerbarth, J., Egawa, J., Schilling, J. M., Platoshyn, O., Zemljic‐Harpf, A., Roth, D. M., Patel, H. H., Patel, P. M., Marsala, M., Head, B. P. Neuron‐targeted caveolin‐1 improves neuromuscular function and extends survival in SOD1G93A mice. FASEB J. 33, 7545–7554 (2019). http://www.fasebj.org

A delicate interneuronal communication between pre- and postsynaptic membranes is critical for synaptic plasticity and the formation of memory. Evidence shows that membrane/lipid rafts (MLRs), plasma membrane microdomains enriched in cholesterol and sphingolipids, organize presynaptic proteins and postsynaptic receptors necessary for synaptic formation and signaling. MLRs establish a cell polarity that facilitates transduction of extracellular cues to the intracellular environment. Here we show that neuron-targeted overexpression of an MLR protein, caveolin-1 (SynCav1), in the adult mouse hippocampus increased the number of presynaptic vesicles per bouton, total excitatory type I glutamatergic synapses, number of same-dendrite multiple-synapse boutons, increased myelination, increased long-term potentiation, and increased MLR-localized N-methyl-d-aspartate receptor subunits (GluN1, GluN2A, and GluN2B). Immunogold electron microscopy revealed that Cav-1 localizes to both the pre- and postsynaptic membrane regions as well as in the synaptic cleft. These findings, which are consistent with a significant increase in ultrastructural and functional synaptic plasticity, provide a fundamental framework that underlies previously demonstrated improvements in learning and memory in adult and aged mice by SynCav1. Such observations suggest that Cav-1 and MLRs alter basic aspects of synapse biology that could serve as potential therapeutic targets to promote neuroplasticity and combat neurodegeneration in a number of neurological disorders.

Vinculin (Vcl) plays a key structural role in ventricular myocytes that, when disrupted, can lead to contractile dysfunction and dilated cardiomyopathy. To investigate the role of Vcl in myocyte and myocardial function, cardiomyocyte-specific Vcl knockout mice (cVclKO) and littermate control wild-type mice were studied with transmission electron microscopy (TEM) and in vivo magnetic resonance imaging (MRI) tagging before the onset of global ventricular dysfunction. MRI revealed significantly decreased systolic strains transverse to the myofiber axis in vivo, but no changes along the muscle fibers or in fiber tension in papillary muscles from heterozygous global Vcl null mice. Myofilament lattice spacing from TEM was significantly greater in cVclKO versus wild-type hearts fixed in the unloaded state. AFM in Vcl heterozygous null mouse myocytes showed a significant decrease in membrane cortical stiffness. A multiscale computational model of ventricular mechanics incorporating cross-bridge geometry and lattice mechanics showed that increased transverse systolic stiffness due to increased lattice spacing may explain the systolic wall strains associated with Vcl deficiency, before the onset of ventricular dysfunction. Loss of cardiac myocyte Vcl may decrease systolic transverse strains in vivo by decreasing membrane cortical tension, which decreases transverse compression of the lattice thereby increasing interfilament spacing and stress transverse to the myofibers.