Research Progress of the Correlation between Caveolin and Unexpected Sudden Cardiac Death / 法医学杂志

Due to the negative autopsy and without cardiac structural abnormalities, unexpected sudden cardiac death （USCD） is always a tough issue for forensic pathological expertise. USCD may be associated with parts of fatal arrhythmic diseases. These arrhythmic diseases may be caused by disorders of cardiac ion channels or channel-related proteins. Caveolin can combine with multiple myocardial ion channel proteins through its scaffolding regions and plays an important role in maintaining the depolarization and repolarization of cardiac action potential. When the structure and function of caveolin are affected by gene mutations or abnormal protein expression, the functions of the regulated ion channels are correspondingly impaired, which leads to the occurrence of multiple channelopathies, arrhythmia or even sudden cardiac death. It is important to study the effects of caveolin on the functions of ion channels for exploring the mechanisms of malignant arrhythmia and sudden cardiac death.

Distribution of caveolin isoforms in the lemur retina

The distribution of caveolin isoforms was previouslyevaluated in the retinas of different species, but has notyet been described in the primate retina. In this study, thedistribution of caveolins was assessed via immunochemistryusing isoform-specific antibodies in the retina of the black-and-white ruffed lemur. Here, we report the presence of avariety of caveolin isoforms in many layers of the lemurretina. As normal human retinas were not available forresearch and the retinas of primates are fairly similar tothose of humans, the lemur retina can be utilized as amodel for caveolin distribution in normal humans.

Evaluation of vasopressin mediated effects on hemostatic mechanisms: relationship with aquaporins and caveolin proteins.

With a view to evaluate the role of AQP-1 and caveolin proteins in the hemostatic actions of vasopressin, hemostasis was evaluated by bleeding and clotting time respectively.Groups of mice and guinea pigs were treated with arginine vasopressin (AVP) and 1-deamino-8D-AVP (DDAVP) to evaluate their effects on the hemostasis. DDAVP and AVP were able to appreciably reduce the bleeding and clotting time after sodium thiopentone, but not effectively after TEA treatment. Animal groups were pretreated with aquaporin-1 (AQP-1) blockers or water deprived to enhance the expression of AQP-1 water channels. Another group of animals were treated with caveolin protein modulators, cholera toxin (CTX) and the effect of vasopressin analogues evaluated. The results suggest that AQP-1 water channels and caveolin proteins contribute to modulate the hemostatic mechanisms of vasopressin.

Calcium sensing receptor forms complex with and is up-regulated by caveolin-1 in cultured human osteosarcoma (Saos-2) cells

The calcium sensing receptor (CaSR) plays an important role for sensing local changes in the extracellular calcium concentration ([Ca2+]o) in bone remodeling. Although the function of CaSR is known, the regulatory mechanism of CaSR remains controversial. We report here the regulatory effect of caveolin on CaSR function as a process of CaSR regulation by using the human osteosarcoma cell line (Saos-2). The intracellular calcium concentration ([Ca2+]i) was increased by an increment of [Ca2+]o. This [Ca2+]i increment was inhibited by the pretreatment with NPS 2390, an antagonist of CaSR. RT-PCR and Western blot analysis of Saos-2 cells revealed the presence of CaSR, caveolin (Cav)-1 and -2 in both mRNA and protein expressions, but there was no expression of Cav-3 mRNA and protein in the cells. In the isolated caveolae-rich membrane fraction from Saos-2 cells, the CaSR, Cav-1 and Cav-2 proteins were localized in same fractions (fraction number 4 and 5). The immuno-precipitation experiment using the respective antibodies showed complex formation between the CaSR and Cav-1, but no complex formation of CaSR and Cav-2. Confocal microscopy also supported the co-localization of CaSR and Cav-1 at the plasma membrane. Functionally, the [Ca2+]o- induced [Ca2+]i increment was attenuated by the introduction of Cav-1 antisense oligodeoxynucleotide (ODN). From these results, in Saos-2 cells, the function of CaSR might be regulated by binding with Cav-1. Considering the decrement of CaSR activity by antisense ODN, Cav-1 up-regulates the function of CaSR under normal physiological conditions, and it may play an important role in the diverse pathophysiological processes of bone remodeling or in the CaSR- related disorders in the body.

Modulation of the caveolin-3 and Akt status in caveolae by insulin resistance in H9c2 cardiomyoblasts

We investigated glucose uptake and the translocation of Akt and caveolin-3 in response to insulin in H9c2 cardiomyoblasts exposed to an experimental insulin resistance condition of 100 nM insulin in a 25 mM glucose containing media for 24 h. The cells under the insulin resistance condition exhibited a decrease in insulin-stimulated 2-deoxy[3 H]glucose uptake as compared to control cells grown in 5 mM glucose media. In addition to a reduction in insulin-induced Akt translocation to membranes, we observed a significant decrease in insulin-stimulated membrane association of phosphorylated Akt with a consequent increase of the cytosolic pool. Actin remodeling in response to insulin was also greatly retarded in the cells. When translocation of Akt and caveolin-3 to caveolae was examined, the insulin resistance condition attenuated localization of Akt and caveolin-3 to caveolae from cytosol. As a result, insulin-stimulated Akt activation in caveolae was significantly decreased. Taken together, our data indicate that the decrease of glucose uptake into the cells is related to their reduced levels of caveolin-3, Akt and phosphorylated Akt in caveolae. We conclude that the insulin resistance condition induced the retardation of their translocation to caveolae and in turn caused an attenuation in insulin signaling, namely activation of Akt in caveolae for glucose uptake into H9c2 cardiomyoblasts.

Co-localization and interaction of organic anion transporter 1 with caveolin-2 in rat kidney

The organic anion transporters (OAT) have recently been identified. Although the some transport properties of OATs in the kidney have been verified, the regulatory mechanisms for OAT's functions are still not fully understood. The rat OAT1 (rOAT1) transports a number of negatively charged organic compounds between the cells and their extracellular milieu. Caveolin (Cav) also plays a role in membrane transport. Therefore, we investigated the protein-protein interactions between rOAT1 and caveolin-2. In the rat kidney, the expressions of rOAT1 mRNA and protein were observed in both the cortex and the outer medulla. With respect to Cav-2, the expressions of mRNA and protein were observed in all portions of the kidney (cortex < outer medulla = inner medulla). The results of Western blot analysis using the isolated caveolae-enriched membrane fractions or the immunoprecipitates by respective antibodies from the rat kidney showed that rOAT1 and Cav-2 co-localized in the same fractions and they formed complexes each other. These results were confirmed by performing confocal microscopy with immunocytochemistry using the primary cultured renal proximal tubular cells. When the synthesized cRNA of rOAT1 along with the antisense oligodeoxynucleotides of Xenopus Cav-2 were co-injected into Xenopus oocytes, the [14C]p-aminohippurate and [3H]methotrexate uptake was slightly, but significantly decreased. The similar results were also observed in rOAT1 over-expressed Chinese hamster ovary cells. These findings suggest that rOAT1 and caveolin-2 are co-expressed in the plasma membrane and rOAT1's function for organic compound transport is upregulated by Cav-2 in the normal physiological condition.