Caveolae-localized signaling microdomains are proposed sites that concentrate G protein-coupled receptors (GPCR), heterotrimeric G-proteins, GPCR/G-protein-regulated effector molecules, and gaseous enzymes involved in generating free radicals and antioxidants, such as heme oxygenase (HO) and nitric oxide synthase (NOS), in a confined region, so as to facilitate coordinated and rapid generation of second messengers and regulation of cell function. The effectiveness of these signaling cascades is dependent upon the organization and location of key signaling proteins within the plasma membrane. Caveolae, 'little caves', a subset of lipid rafts, are cholesterol- and sphingolipid-enriched 50-100 nm invaginations of the plasma membrane that contain isoforms of the structural protein caveolin (Cav-1, -2, and -3). Defining the localization and interaction of GPCR and gaseous signaling components in normal adult cardiac myocytes (CM) is thus essential for understanding signaling cascades that regulate developmental and pathological changes in the heart. Microtubules and microfilaments help regulate plasma membrane topography but their role in compartmentation of caveolar-resident signaling components involved in cAMP production has not been defined. The present study used adult rat cardiac myocytes (CM) to investigate whether (1) GPCR, G-proteins, effector enzymes, and gaseous signaling components (heme oxygenase (HO) and endothelial nitric oxide synthase (eNOS)) involved in free radical generation, localize with caveolin in both sarcolemmal and intracellular membrane regions, and (2) if cytoskeletal disruption influences localization of caveolin (Cav) and expression of caveolae, thereby altering the distribution of G protein-coupled receptor (GPCR) signaling components and cAMP production. The observed distribution of GPCRs, G-proteins, and AC with Cav-3 on both sarcolemmal and intracellular regions defines unique cellular microdomains for regulation and signaling by hormones and drugs in the adult heart. The localization of HO-1 and eNOS with caveolin, and the close apposition between caveolae and mitochondria suggests that caveolae in addition to being sites that generate gaseous signaling components (i.e. CO and NO) may also be sites for generation of antioxidants (biliverdin), and thus 'sinks' for free radicals in adult CM. Disruption microtubules and microfilaments alters the expression of caveolae, phosphorylation state of caveolins, and ability of caveolins to blunt GPCR-AC signal transduction

The plasma membrane in eukaryotic cells contains microdomains that are enriched in certain glycosphingolipids, gangliosides, and sterols (such as cholesterol) to form membrane/lipid rafts (MLR). These regions exist as caveolae, morphologically observable flask-like invaginations, or as a less easily detectable planar form. MLR are scaffolds for many molecular entities, including signaling receptors and ion channels that communicate extracellular stimuli to the intracellular milieu. Much evidence indicates that this organization and/or the clustering of MLR into more active signaling platforms depends upon interactions with and dynamic rearrangement of the cytoskeleton. Several cytoskeletal components and binding partners, as well as enzymes that regulate the cytoskeleton, localize to MLR and help regulate lateral diffusion of membrane proteins and lipids in response to extracellular events (e.g., receptor activation, shear stress, electrical conductance, and nutrient demand). MLR regulate cellular polarity, adherence to the extracellular matrix, signaling events (including ones that affect growth and migration), and are sites of cellular entry of certain pathogens, toxins and nanoparticles. The dynamic interaction between MLR and the underlying cytoskeleton thus regulates many facets of the function of eukaryotic cells and their adaptation to changing environments. Here, we review general features of MLR and caveolae and their role in several aspects of cellular function, including polarity of endothelial and epithelial cells, cell migration, mechanotransduction, lymphocyte activation, neuronal growth and signaling, and a variety of disease settings. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.

Caveolins have been recognized over the past few decades as key regulators of cell physiology. They are ubiquitously expressed and regulate a number of processes that ultimately impact efficiency of cellular processes. Though not critical to life, they are central to stress adaptation in a number of organs. The following review will focus specifically on the role of caveolin in stress adaptation in the heart, brain, and eye, three organs that are susceptible to acute and chronic stress and that show as well declining function with age. In addition, we consider some novel molecular mechanisms that may account for this stress adaptation and also offer potential to drive the future of caveolin research.

Atrophy is thought to be a primary mode of muscle loss in neuromuscular injuries. The differential effects of central and peripheral injuries on atrophy and degeneration/regeneration in skeletal muscle tissue have not been well described. This study investigated skeletal muscle atrophy and degeneration/regeneration in an animal model of traumatic brain injury (TBI). Eight 8-month-old wild-type C57BL6 mice underwent either a sham craniotomy or TBI targeting the motor cortex. Atrophy (fiber area; FA) and degeneration/regeneration (centralized nuclei proportions; CN) of the soleus and tibialis anterior (TA) muscles were measured 2 months post-injury. Injured soleus FAs were smaller than sham soleus (p = 0.02) and injured TA (p < 0.001). Mean CNs were higher in the TBI-injured TA than in other muscles. Differential TBI-induced atrophy and degeneration/regeneration in lower limb muscles suggests that muscle responses to cortical injury involve more complex changes than those observed with simple disuse atrophy.

Mitochondrial dysfunction plays a pivotal role in the Alzheimer's Disease (AD) pathology. Disrupted mitochondrial dynamics (i.e., fusion/fission balance), which are essential for normal mitochondria structure and function, are documented in AD. Caveolin-1 (Cav-1), a membrane/lipid raft (MLR) scaffolding protein regulates metabolic pathways in several different cell types such as hepatocytes and cancer cells. Previously, we have shown decreased expression of Cav-1 in the hippocampus of 9-month (m) old PSAPP mice, while hippocampal overexpression of neuron-targeted Cav-1 using the synapsin promoter (i.e., SynCav1) preserved cognitive function, neuronal morphology, and synaptic ultrastructure in 9 and 12 m PSAPP mice. Considering the central role of energy production in maintaining normal neuronal and synaptic function and survival, the present study reveals that PSAPP mice exhibit disrupted mitochondrial distribution, morphometry, and respiration. In contrast, SynCav1 mitigates mitochondrial damage and loss and enhances mitochondrial respiration. Furthermore, by examining mitochondrial dynamics, we found that PSAPP mice showed a significant increase in the phosphorylation of mitochondrial dynamin-related GTPase protein (DRP1), resulting in excessive mitochondria fragmentation and dysfunction. In contrast, hippocampal delivery of SynCav1 significantly decreased p-DRP1 and augmented the level of the mitochondrial fusion protein, mitofusin1 (Mfn1) in PSAPP mice, a molecular event, which may mechanistically explain for the preserved balance of mitochondria fission/fusion and metabolic resilience in 12 m PSAPP-SynCav1 mice. Our data demonstrate the critical role for Cav-1 in maintaining normal mitochondrial morphology and function through affecting mitochondrial dynamics and explain a molecular and cellular mechanism underlying the previously reported neuroprotective and cognitive preservation induced by SynCav1 in PSAPP mouse model of AD.

Investigations of Alzheimer's disease (AD), traumatic brain injury (TBI), and related brain disorders have provided extensive evidence for involvement of cathepsin B, a lysosomal cysteine protease, in mediating the behavioral deficits and neuropathology of these neurodegenerative diseases. This review integrates findings of cathepsin B regulation in clinical biomarker studies, animal model genetic and inhibitor evaluations, structural studies, and lysosomal cell biological mechanisms in AD, TBI, and related brain disorders. The results together indicate the role of cathepsin B in the behavioral deficits and neuropathology of these disorders. Lysosomal leakage occurs in AD and TBI, and related neurodegeneration, which leads to the hypothesis that cathepsin B is redistributed from the lysosome to the cytosol where it initiates cell death and inflammation processes associated with neurodegeneration. These results together implicate cathepsin B as a major contributor to these neuropathological changes and behavioral deficits. These findings support the investigation of cathepsin B as a potential drug target for therapeutic discovery and treatment of AD, TBI, and TBI-related brain disorders.

Dopamine D1 receptor (D1R) function is regulated by membrane/lipid raft-resident protein caveolin-1 (Cav1). We examined whether altered expression of Cav1 in the dorsal striatum would affect self-administration of methamphetamine, an indirect agonist at the D1Rs. A lentiviral construct expressing Cav1 (LV-Cav1) or containing a short hairpin RNA against Cav1 (LV-shCav1) was used to overexpress or knock down Cav1 expression respectively, in the dorsal striatum. Under a fixed-ratio schedule, LV-Cav1 enhanced and LV-shCav1 reduced responding for methamphetamine in an extended access paradigm compared to LV-GFP controls. LV-Cav1 and LV-shCav1 also produced an upward and downward shift in a dose-response paradigm, generating a drug vulnerable/resistant phenotype. LV-Cav1 and LV-shCav1 did not alter responding for sucrose. Under a progressive-ratio schedule, LV-shCav1 generally reduced positive-reinforcing effects of methamphetamine and sucrose as seen by reduced breakpoints. Western blotting confirmed enhanced Cav1 expression in LV-Cav1 rats and reduced Cav1 expression in LV-shCav1 rats. Electrophysiological findings in LV-GFP rats demonstrated an absence of high-frequency stimulation (HFS)-induced long-term potentiation (LTP) in the dorsal striatum after extended access methamphetamine self-administration, indicating methamphetamine-induced occlusion of plasticity. LV-Cav1 prevented methamphetamine-induced plasticity via increasing phosphorylation of calcium calmodulin kinase II, suggesting a mechanism for addiction vulnerability. LV-shCav1 produced a marked deficit in the ability of HFS to produce LTP and, therefore, extended access methamphetamine was unable to alter striatal plasticity, indicating a mechanism for resistance to addiction-like behavior. Our results demonstrate that Cav1 expression and knockdown driven striatal plasticity assist with modulating addiction to drug and nondrug rewards, and inspire new strategies to reduce psychostimulant addiction.

Cirrhotic cardiomyopathy is a clinical syndrome in patients with liver cirrhosis characterized by blunted cardiac contractile responses to stress and/or heart rate-corrected QT (QTc) interval prolongation. Caveolin-3 (Cav-3) plays a critical role in cardiac protection and is an emerging therapeutic target for heart disease. We investigated the protective role of cardiac-specific overexpression (OE) of Cav-3 in cirrhotic cardiomyopathy. Biliary fibrosis was induced in male Cav-3 OE mice and transgene negative (TG_neg) littermates by feeding a diet containing 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC; 0.1%) for 3 wk. Liver pathology and blood chemistries were assessed, and stress echocardiography, telemetry, and isolated heart perfusion studies to assess adrenergic responsiveness were performed. Cav-3 OE mice showed a similar degree of hyperdynamic contractility, pulmonary hypertension, and QTc interval prolongation as TG_neg mice after 3 wk of DDC diet. Blunted systolic responses were shown in both DDC-fed Cav-3 OE and TG_neg hearts after in vivo isoproterenol challenge. However, QTc interval prolongation after in vivo isoproterenol challenge was significantly less in DDC-fed Cav-3 OE hearts compared with DDC-fed TG_neg hearts. In ex vivo perfused hearts, where circulatory factors are absent, isoproterenol challenge showed hearts from DDC-fed Cav-3 OE mice had better cardiac contractility and relaxation compared with DDC-fed TG_neg hearts. Although Cav-3 OE in the heart did not prevent cardiac alterations in DDC-induced biliary fibrosis, cardiac expression of Cav-3 reduced QTc interval prolongation after adrenergic stimulation in cirrhosis.NEW & NOTEWORTHY Prevalence of cirrhotic cardiomyopathy is up to 50% in cirrhotic patients, and liver transplantation is the only treatment. However, cirrhotic cardiomyopathy is associated with perioperative morbidity and mortality after liver transplantation; therefore, management of cirrhotic cardiomyopathy is crucial for successful liver transplantation. This study shows cardiac myocyte specific overexpression of caveolin-3 (Cav-3) provides better cardiac contractile responses and less corrected QT prolongation during adrenergic stress in a cirrhotic cardiomyopathy model, suggesting beneficial effects of Cav-3 expression in cirrhotic cardiomyopathy.

The author reports that data for electrophysiology findings reported in Figs. 4 and 5 for control group and Meth Rst group have been published previously (Galinato MH et al., J Neurosci. 2018 Feb 21; 38(8):2029-2042.