Caveolae regulate vasoconstriction of conduit arteries to angiotensin II in hindlimb unweighted rats

Caveolae and lipid sorting: Shaping the cellular response to stress

Caveolae are an abundant and characteristic surface feature of many vertebrate cells. The uniform shape of caveolae is characterized by a bulb with consistent curvature connected to the plasma membrane (PM) by a neck region with opposing curvature. Caveolae act in mechanoprotection by flattening in response to increased membrane tension, and their disassembly influences the lipid organization of the PM. Here, we review evidence for caveolae as a specialized lipid domain and speculate on mechanisms that link changes in caveolar shape and/or protein composition to alterations in specific lipid species. We propose that high membrane curvature in specific regions of caveolae can enrich specific lipid species, with consequent changes in their localization upon caveolar flattening. In addition, we suggest how changes in the association of lipid-binding caveolar proteins upon flattening of caveolae could allow release of specific lipids into the bulk PM. We speculate that the caveolae-lipid system has evolved to function as a general stress-sensing and stress-protective membrane domain.

BKCa compensates impaired coronary vasoreactivity through RhoA/ROCK pathway in hind-limb unweighted rats

Previous studies have demonstrated cardiac and vascular remodeling induced by microgravity exposure. Yet, as the most important branch of vasculatures circulating the heart, the coronary artery has been seldomly studied about its adaptations under microgravity conditions. Large-conductance Ca²⁺-activated potassium channel (BK_Ca) and the Ras homolog family member A (RhoA)/Rho kinase (ROCK) pathway play key roles in control of vascular tone and mediation of microgravity-induced vascular adjustments. Therefore, we investigated the adaptation of coronary vasoreactivity to simulated microgravity and the role of BK_Ca and the RhoA/ROCK pathway in it. Four-week-old hind-limb unweighted (HU) rats were adopted to simulate effects of microgravity. Right coronary artery (RCA) constriction was measured by isometric force recording. The activity and expression of BK_Ca and the RhoA/ROCK pathway were examined by Western blot, patch-clamp recordings, and immunoprecipitation. We found HU significantly decreased RCA vasoconstriction to KCl, serotonin, and U-46619, but increased protein expression and current densities of BK_Ca, inhibition of which by iberiotoxin (IBTX) further decreased RCA vasoconstriction (P < 0.05). Expression of RhoA and ROCK as well as active RhoA and phosphorylation of myosin light chain (MLC) at Ser¹⁹ and MLC phosphatase target-1 at Thr⁶⁹⁶ were significantly increased by HU, and ROCK inhibitor Y-27632 exerted greater suppressing effect on HU RCA vasoconstriction than that of control (P < 0.05). BK_Ca opener NS1619 increased HU RCA vasoconstriction, which was blocked by both RhoA and ROCK inhibitor, similar to the effect of IBTX. These results indicate that HU impairs coronary vasoconstriction but enhances BK_Ca activity acting as a protective mechanism avoiding excessive decrease of coronary vasoreactivity through activation of the RhoA/ROCK pathway.-Wu, Y., Yue, Z., Wang, Q., Lv, Q., Liu, H., Bai, Y., Li, S., Xie, M., Bao, J., Ma, J., Zhu, X., Wang, Z. BK_Ca compensates impaired coronary vasoreactivity through RhoA/ROCK pathway in hind-limb unweighted rats.

Focal adhesions are involved in simulated-microgravity-induced basilar and femoral arterial remodelling in rats

Recent studies have suggested that microgravity-induced arterial remodelling contributes to post-flight orthostatic intolerance and that multiple mechanisms are involved in arterial remodelling. However, the initial mechanism by which haemodynamic changes induce arterial remodelling is unknown. Focal adhesions (FAs) are dynamic protein complexes that have mechanotransduction properties. This study aimed to investigate the role of FAs in simulated-microgravity-induced basilar and femoral arterial remodelling. A 4-week hindlimb-unweighted (HU) rat model was used to simulate the effects of microgravity, and daily 1-hour intermittent artificial gravity (IAG) was used to prevent arterial remodelling. After 4-week HU, wall thickness, volume of smooth muscle cells (SMCs) and collagen content were increased in basilar artery but decreased in femoral artery (P < 0.05). Additionally, the expression of p-FAK Y397 and p-Src Y418 was increased and reduced in SMCs of basilar and femoral arteries, respectively, by HU (P < 0.05). The number of FAs was increased in basilar artery and reduced in femoral artery by HU (P < 0.05). Furthermore, daily 1-hour IAG prevented HU-induced differential structural adaptations and changes in FAs of basilar and femoral arteries. These results suggest that FAs may act as mechanosensors in arterial remodelling by initiating intracellular signal transduction in response to altered mechanical stress induced by microgravity.

Acid sphingomyelinase/ceramide regulates carotid intima-media thickness in simulated weightless rats

Structural adaptation of arteries to weightlessness might lower the working ability or even threaten the physical health of astronauts, but the underlying mechanism is unclear. Acid sphingomyelinase (ASM) catalyzes ceramide (Cer) generation controlling arterial remodeling through multiple signaling pathways. In the present study, we aimed to investigate the contribution of ASM/Cer to the changes of common carotid artery intima-media thickness (CIMT) induced by simulated weightlessness. Hindlimb-unloaded tail-suspended (HU) rats were used to simulate the effect of weightlessness. Morphology of the carotid artery (CA) was examined by hematoxylin-eosin staining. Protein content of ASM or proliferating cell nuclear antigen (PCNA) was detected by Western blot. Cer level was measured by immunohistochemistry analysis. Apoptosis events were observed by transferase-mediated dUTP nick end labeling (TUNEL) staining. During 4 weeks of tail suspension, CIMT was increased gradually in HU but not in their synchronous control rats (P < 0.05). Correspondingly, the CA of HU rats had a lower apoptosis and higher proliferation of vascular smooth muscle cells (VSMCs). As compared to the control, both ASM protein expression and Cer content were reduced significantly in CA of HU rats (P < 0.05), incubation of which with permeable Cer reversed the changes in apoptosis and proliferation substantially. Furthermore, when the ASM protein content as well as Cer level in CA of control rats was diminished by using an ASM inhibitor, an increase of CIMT along with reduced apoptosis and enhanced proliferation of VSMCs was found. Our results suggest that by controlling the balance between apoptosis and proliferation, ASM/Cer plays an important role in the regulation of CIMT during simulated weightlessness.