Caveolin-1 Expression Ameliorates Nephrotic Damage in a Rabbit Model of Cholesterol-Induced Hypercholesterolemia

Cav-1 regulates the bile salt export pump on the canalicular membrane of hepatocytes by PKCα-associated signalling under cholesterol stimulation

BACKGROUND AND AIMS

The secretion of bile salts transported by the bile salt export pump (BSEP) is the primary driving force for the generation of bile flow; thus, it is closely related to the formation of cholesterol stones. Caveolin-1 (Cav-1), an essential player in cell signalling and endocytosis, is known to co-localize with cholesterol-rich membrane domains. This study illustrates the role of Cav-1 and BSEP in cholesterol stone formation.

METHODS

Adult male C57BL/6 mice were used as an animal model. HepG2 cells were cultured under different cholesterol concentrations and BSEP, Cav-1, p-PKCα and Hax-1 expression levels were determined via Western blotting. Expression levels of BSEP and Cav-1 mRNA were detected using real-time PCR. Immunofluorescence and immunoprecipitation assays were performed to study BSEP and Hax-1 distribution. Finally, an ATPase activity assay was performed to detect BSEP transport activity under different cholesterol concentrations in cells.

RESULTS

Under low-concentration stimulation with cholesterol, Cav-1 and BSEP protein and mRNA expression levels significantly increased, PKCα phosphorylation significantly decreased, BSEP binding capacity to Hax-1 weakened, and BSEP function increased. Under high-concentration stimulation with cholesterol, Cav-1 and BSEP protein and mRNA expression levels decreased, PKCα phosphorylation increased, BSEP binding capacity to Hax-1 rose, and BSEP function decreased.

CONCLUSION

Cav-1 regulates the bile salt export pump on the canalicular membrane of hepatocytes via PKCα-associated signalling under cholesterol stimulation.

Cyclophilin A accelerates SiO2-induced macrophage foaming

Silicosis is a common occupational disease characterized by lung inflammation, fibrosis and pulmonary dysfunction caused by long-term inhalation of free SiO₂. Cell foaming and the change of CyPA have been observed in SiO₂-induced macrophages, but the specific mechanism of CyPA in SiO₂-induced foam cells remains poorly understood. The purpose of this study is to explore the mechanism of CyPA in SiO₂-induced macrophage foaming and its effect on silicosis. We found that overexpression of CyPA promoted the macrophage foaming and the expression of COL I and α-SMA, while silencing CyPA inhibites the macrophage foaming and the expression of COL I and α-SMA. After blocking the expression of CD36 on the basis of overexpression CyPA, we found it inhibites the macrophage foaming. In conclusion, CyPA can affect the foaming of macrophages and may participate in silicosis fibrosis.

Caveolin-1 Regulates Cellular Metabolism: A Potential Therapeutic Target in Kidney Disease

The kidney is an energy-consuming organ, and cellular metabolism plays an indispensable role in kidney-related diseases. Caveolin-1 (Cav-1), a multifunctional membrane protein, is the main component of caveolae on the plasma membrane. Caveolae are represented by tiny invaginations that are abundant on the plasma membrane and that serve as a platform to regulate cellular endocytosis, stress responses, and signal transduction. However, caveolae have received increasing attention as a metabolic platform that mediates the endocytosis of albumin, cholesterol, and glucose, participates in cellular metabolic reprogramming and is involved in the progression of kidney disease. It is worth noting that caveolae mainly depend on Cav-1 to perform the abovementioned cellular functions. Furthermore, the mechanism by which Cav-1 regulates cellular metabolism and participates in the pathophysiology of kidney diseases has not been completely elucidated. In this review, we introduce the structure and function of Cav-1 and its functions in regulating cellular metabolism, autophagy, and oxidative stress, focusing on the relationship between Cav-1 in cellular metabolism and kidney disease; in addition, Cav-1 that serves as a potential therapeutic target for treatment of kidney disease is also described.

Low Pre-Transplant Caveolin-1 Serum Concentrations Are Associated with Acute Cellular Tubulointerstitial Rejection in Kidney Transplantation

Acute and chronic transplant rejections due to alloreactivity are essential contributors to graft loss. However, the strength of alloreactivity is biased by non-immunological factors such as ischemia reperfusion injury (IRI). Accordingly, protection from IRI could be favorable in terms of limiting graft rejection. Caveolin-1 (Cav-1) is part of the cell membrane and an important regulator of intracellular signaling. Cav-1 has been demonstrated to limit IRI and to promote the survival of a variety of cell types including renal cells under stress conditions. Accordingly, Cav-1 could also play a role in limiting anti-graft immune responses. Here, we evaluated a possible association between pre-transplant serum concentrations of Cav-1 and the occurrence of rejection during follow-up in a pilot study. Therefore, Cav-1-serum concentrations were analyzed in 91 patients at the time of kidney transplantation and compared to the incidence of acute and chronic rejection. Higher Cav-1 levels were associated with lower occurrence of acute cellular tubulointerstitial rejection episodes.

The effect of hyperlipidemia on bone graft regeneration of peri-implantal created defects in rabbits

Aim

It is reported that hyperlipidemia affects quality and density of bone and adversely affects wound healing. The effect of hyperlipidemia on implant osseointegration and peri-implant defect regeneration has not been fully explained. The purpose of this study was to examine the effects of hyperlipidemia on the healing potential of the materials used for peri-implant bone regeneration and implant stability.

Materials and methods

Twelve male, New Zealand rabbits were used in this study. Half of the rabbits were fed a 2% cholesterol diet for 8 weeks to induce hypercholesterolemia. Peri-implant defects (7 mm diameter) were created in the tibias of rabbits and placed implants (3.3 mm in diameter). This study was conducted as a split-mouth design. Animals were randomly divided into two groups: (1) hypercholesterol+autogenous graft group and hypercholesterol+xenograft group (n = 6), and (2) autogenous graft and xenograft groups as controls (n = 6). At 8 weeks after surgery, the rabbits were euthanized. During implant surgery and at 8 weeks, implant stability was measured with resonance frequency analysis (RFA values). Bone-to-implant contact (BIC) was analyzed via histomorphometric analysis.

Results

Hyperlipidemic groups showed significantly lower BIC values than those of the control groups at 8 weeks (p < 0.05). According to baseline RFA readings, there was no significant difference between control and hyperlipidemic groups (p ˃ 0.05). The hypercholesterol+autogenous graft group had significantly lower RFA readings and BIC values than the hypercholesterol+xenograft group at 8 weeks (p < 0.05).

Conclusion

Within the limitations of this study, it was found that hyperlipidemia may negatively affect the implant stability especially in the autogenous group and also, may decrease peri-implant bone regeneration. However, further studies are necessary to confirm these results more.

The influence of lipoic acid on caveolin-1-regulated antioxidative enzymes in the mouse model of acute ulcerative colitis

AIM

This study was undertaken to verify if two-weeks treatment of lipoic acid (LA) influence colon damage and pro-inflammatory cytokine synthesis during DSS-induced acute colitis. Moreover, as LA has anti-oxidative properties, we analyzed its influence on the level of antioxidative enzymes, HO-1 and eNOS, and their regulator- caveolin-1.

METHODS

LA was administrated to male C57/BALBc mice at a dose of 25 or 50mg/kg/day (i.p.) for 21days. Acute colitis was induced by administration of 4% DSS (w/v) in drinking water for 5days, followed by 2days of normal drinking water. Mice in LA+DSS groups were treated with LA (25 or 50mg/kg/day; i.p.) starting 14days prior to 4% DSS. Control group received saline for 21days. In the colon tissue we measured myeloperoxidase activity (MPO), IL-1β, IL-6, IL-17A, IL-23 (ELISA method), and tissue level of cav-1, phospho-eNOS, total eNOS and HO-1 (Western blot).

RESULTS

Administration of DSS significantly increased total colon damage (p<0.001), myeloperoxidase (MPO) activity (p<0.05) and pro-inflammatory IL-6 (p<0.05). There was also a tendency towards higher IL-1β, IL-17A, and IL-23 in the colon. LA alone did not influence total colon damage, MPO activity, and pro-inflammatory cytokines concentration compared to control (p<0.05). Notably, mice treated with LA and DSS had significantly decreased total colon damage score (p<0.001), despite augmented colon MPO activity (p<0.01), but similar (IL-17A) or even significantly higher level (IL-1β, IL-23) as compared to the DSS group (p<0.05). IL-6 was insignificantly decreased after LA treatment at a dose of 50mg/kg. In acute colitis there was a tendency towards an increase in cav-1 and HO-1 and a decrease p-eNOS/total eNOS ratio. Moreover, the LA+DSS groups had higher expression of HO-1 and p-eNOS/total eNOS (p<0.05) compared to the DSS group, and a tendency towards higher cav-1 level. The changes did not depend on LA dose.

CONCLUSION

Our study indicated that LA, at lower doses, may influence cav-1-regulated antioxidative enzyme levels (HO-1 and p-eNOS/total eNOS) despite an increase in colon pro-inflammatory cytokine levels during acute colitis. Hence, LA treatment may be - to some extent - beneficial in attenuation of acute colitis.