Caveolin 1-related autophagy initiated by aldosterone-induced oxidation promotes liver sinusoidal endothelial cells defenestration

Endothelial cell serum and glucocorticoid regulated kinase 1 (SGK1) mediates vascular stiffening

BACKGROUND

Excessive dietary salt intake increases vascular stiffness in humans, especially in salt-sensitive populations. While we recently suggested that the endothelial sodium channel (EnNaC) contributes to salt-sensitivity related endothelial cell (EC) and arterial stiffening, mechanistic understanding remains incomplete. This study therefore aimed to explore the role of EC-serum and glucocorticoid regulated kinase 1 (SGK1), as a reported regulator of sodium channels, in EC and arterial stiffening.

METHODS AND RESULTS

A mouse model of salt sensitivity-associated vascular stiffening was produced by subcutaneous implantation of slow-release deoxycorticosterone acetate (DOCA) pellets, with salt (1 % NaCl, 0.2 % KCl) administered via drinking water. Preliminary data showed that global SGK1 deletion caused significantly decreased blood pressure (BP), EnNaC activity and aortic endothelium stiffness as compared to control mice following DOCA-salt treatment. To probe EC signaling pathways, selective deletion of EC-SGK1 was performed by cross-breeding cadherin 5-Cre mice with sgk1flox/flox mice. DOCA-salt treated control mice had significantly increased BP, EC and aortic stiffness in vivo and ex vivo, which were attenuated by EC-SGK1 deficiency. To demonstrate relevance to humans, human aortic ECs were cultured in the absence or presence of aldosterone and high salt with or without the SGK1 inhibitor, EMD638683 (10uM or 25uM). Treatment with aldosterone and high salt increased intrinsic stiffness of ECs, which was prevented by SGK1 inhibition. Further, the SGK1 inhibitor prevented aldosterone and high salt induced actin polymerization, a key mechanism in cellular stiffening.

CONCLUSION

EC-SGK1 contributes to salt-sensitivity related EC and aortic stiffening by mechanisms appearing to involve regulation of actin polymerization.

Oxidized phospholipid POVPC contributes to vascular calcification by triggering ferroptosis of vascular smooth muscle cells

Vascular calcification is an actively regulated biological process resembling bone formation, and osteogenic differentiation of vascular smooth muscle cells (VSMCs) plays a crucial role in this process. 1-Palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC), an oxidized phospholipid, is found in atherosclerotic plaques and has been shown to induce oxidative stress. However, the effects of POVPC on osteogenic differentiation and calcification of VSMCs have yet to be studied. In the present study, we investigated the role of POVPC in vascular calcification using in vitro and ex vivo models. POVPC increased mineralization of VSMCs and arterial rings, as shown by alizarin red staining. In addition, POVPC treatment increased expression of osteogenic markers Runx2 and BMP2, indicating that POVPC promotes osteogenic transition of VSMCs. Moreover, POVPC increased oxidative stress and impaired mitochondria function of VSMCs, as shown by increased ROS levels, impairment of mitochondrial membrane potential, and decreased ATP levels. Notably, ferroptosis triggered by POVPC was confirmed by increased levels of intracellular ROS, lipid ROS, and MDA, which were decreased by ferrostatin-1, a ferroptosis inhibitor. Furthermore, ferrostatin-1 attenuated POVPC-induced calcification of VSMCs. Taken together, our study for the first time demonstrates that POVPC promotes vascular calcification via activation of VSMC ferroptosis. Reducing the levels of POVPC or inhibiting ferroptosis might provide a novel strategy to treat vascular calcification.

Autophagic degradation of MVBs in LSECs promotes Aldosterone induced-HSCs activation

BACKGROUND AND AIMS

The important role of extracellular vesicles (EVs) in liver fibrosis has been confirmed. However, EVs derived from liver sinusoidal endothelial cells (LSECs) in the activation of hepatic stellate cells (HSCs) and liver fibrosis is still unclear. Our previous work demonstrated that Aldosterone (Aldo) may have the potential to regulate EVs from LSECs via autophagy pathway. Thus, we aim to investigate the role of Aldo in the regulation of EVs derived from LSECs.

APPROACH AND RESULTS

Using an Aldo-continuous pumping rat model, we observed that Aldo-induced liver fibrosis and capillarization of LSECs. In vitro, transmission electron microscopy (TEM) revealed that stimulation of Aldo led to the upregulation of autophagy and degradation of multivesicular bodies (MVBs) in LSECs. Mechanistically, Aldo upregulated ATP6V0A2, which promoted lysosomal acidification and subsequent autophagy in LSECs. Inhibiting autophagy with si-ATG5 adeno-associated virus (AAV) in LSECs effectively mitigated Aldo-induced liver fibrosis in rats. RNA sequencing and nanoparticle tracking (NTA) analyses of EVs derived from LSECs indicated that Aldo result in a decrease in both the quantity and quality of EVs. We also observed a reduction in the protective miRNA-342-5P in EVs derived from Aldo-treated LSECs, which may play a critical role in HSCs activation. Target knockdown of EV secretion with si-RAB27a AAV in LSECs led to the development of liver fibrosis and HSC activation in rats.

CONCLUSION

Aldo-induced Autophagic degradation of MVBs in LSECs promotes a decrease in the quantity and quality of EVs derived from LSECs, resulting in the activation of HSCs and liver fibrosis under hyperaldosteronism. Modulating the autophagy level of LSECs and their EV secretion may represent a promising therapeutic approach for treating liver fibrosis.

Seawater pearl hydrolysate inhibits photoaging via decreasing oxidative stress, autophagy and apoptosis of Ultraviolet B-induced human skin keratinocytes

BACKGROUND

Ultraviolet (UV) is the main reason to cause photoaging skin which not only hinders beauty, brings the patients with psychological burden, but also pathologically leads to the occurrence of tumors in skin.

OBJECTIVE

This study goes into the inhibitory effect and mechanism of seawater pearl hydrolysate (SPH) to address human skin keratinocytes photoaging induced by UVB.

METHODS

The photoaging model of Hacat cell was constructed by UVB irradiation, the levels of oxidative stress, apoptosis, aging, autophagy and autophagy-related protein and signal pathway expression were assessed to characterize the inhibitory effect and mechanism of SPH on photoaging Hacat cell.

RESULTS

Seawater pearl hydrolysate significantly accelerated (p < 0.05) the activities of superoxide dismutase, catalase, and glutathione peroxidase, and markedly reduced (p < 0.05) the contents of reactive oxygen species (ROS), malondialdehyde, protein carbonyl compound and nitrosylated tyrosine protein, aging level, apoptosis rate in Hacat cell induced by 200 mJ cm-2 UVB after 24 and 48 h of culture; high dose SPH significantly raised (p < 0.05) relative expression level of p-Akt, p-mTOR proteins, and markedly decreased (p < 0.05) relative expression level of LC3II protein, p-AMPK, and autophagy level in Hacat cell induced by 200 mJ cm-2 UVB, or in combination with the intervention of PI3K inhibitor or AMPK overexpression after 48 h of culture.

CONCLUSION

Seawater pearl hydrolysate can effectively inhibit 200 mJ cm-2 UVB-induced photoaging of Hacat cells. The mechanism indicates removing the excessive ROS through increasing the antioxidation of photoaging Hacat cells. Once redundant ROS is eliminated, SPH works to reduce AMPK, increase PI3K-Akt pathway expression, activate mTOR pathway to lowdown autophagy level, and as a result, inhibit apoptosis and aging in photoaging Hacat cells.

The unique structural and functional characteristics of glomerular endothelial cell fenestrations and their potential as a therapeutic target in kidney disease

Glomerular endothelial cell (GEnC) fenestrations are a critical component of the glomerular filtration barrier. Their unique nondiaphragmed structure is key to their function in glomerular hydraulic permeability, and their aberration in disease can contribute to loss of glomerular filtration function. This review provides a comprehensive update of current understanding of the regulation and biogenesis of fenestrae. We consider diseases in which GEnC fenestration loss is recognized or may play a role and discuss methods with potential to facilitate the study of these critical structures. Literature is drawn from GEnCs as well as other fenestrated cell types such as liver sinusoidal endothelial cells that most closely parallel GEnCs.

Protein components of maple syrup as a potential resource for the development of novel anti‑colorectal cancer drugs

Maple syrup is a natural sweetener consumed worldwide. Active ingredients of maple syrup possess antitumor effects; however, these ingredients are phenolic compounds. The present study aimed to investigate components other than phenolic compounds that may have antitumor effects against colorectal cancer (CRC). Cell proliferation assays demonstrated that treatment with the more than 10,000 molecular weight fraction significantly inhibited viability in DLD‑1 cells. Therefore, we hypothesized that the protein components of maple syrup may be the active ingredients in maple syrup. We obtained protein components from maple syrup by ammonium sulfate precipitation, and treatment with the protein fraction of maple syrup (MSpf) was found to exhibit a potential antitumor effect. MSpf‑treated DLD‑1 colon adenocarcinoma cells exhibited significantly decreased proliferation, migration and invasion. In addition, upregulation of LC3A and E‑cadherin and downregulation of MMP‑9 expression levels were observed following MSpf treatment. Investigation of the components of MSpf suggested that it was primarily formed of advanced glycation end products (AGEs). Therefore, whether AGEs in MSpf affected the STAT3 pathway through the binding to its receptor, receptor of AGE (RAGE), was assessed. MSpf treatment was associated with decreased RAGE expression and STAT3 phosphorylation. Finally, to determine whether autophagy contributed to the inhibitory effect of cell proliferation following MSpf treatment, the effect of MSpf treatment on autophagy induction following bafilomycin A1 treatment, a specific autophagy inhibitor, was assessed. The inhibitory effect of MSpf treatment on cell proliferation was enhanced through the inhibition of autophagy by bafilomycin A1 treatment. These results suggested that AGEs in MSpf suppressed cell proliferation and epithelial‑mesenchymal transition through inhibition of the STAT3 signaling pathway through decreased RAGE expression. Therefore, AGEs in MSpf may be potential compounds for the development of antitumor drugs for the treatment of CRC with fewer adverse effects compared with existing antitumor drugs.

Maternal hepatic immunology during pregnancy

The liver plays pivotal roles in immunologic responses, and correct hepatic adaptations in maternal immunology are required during pregnancy. In this review, we focus on anatomical and immunological maternal hepatic adaptations during pregnancy, including our recent reports in this area. Moreover, we summarize maternal pregnancy-associated liver diseases, including hyperemesis gravidarum; intrahepatic cholestasis of pregnancy; preeclampsia, specifically hemolysis, elevated liver enzymes, and low platelet count syndrome; and acute fatty liver of pregnancy. In addition, the latest information about the factors that regulate hepatic immunology during pregnancy are reviewed for the first time, including human chorionic gonadotropin, estrogen, progesterone, growth hormone, insulin like growth factor 1, oxytocin, adrenocorticotropic hormone, adrenal hormone, prolactin, melatonin and prostaglandins. In summary, the latest progress on maternal hepatic anatomy and immunological adaptations, maternal pregnancy-associated diseases and the factors that regulate hepatic immunology during pregnancy are discussed, which may be used to prevent embryo loss and abortion, as well as pregnancy-associated liver diseases.

Nucleophagic Degradation of Progerin Ameliorates Defenestration in Liver Sinusoidal Endothelium Due to SIRT1-Mediated Deacetylation of Nuclear LC3

Progerin, a permanently farnesylated prelamin A protein in cell nuclei, is potentially implicated in the defenestration of liver sinusoidal endothelial cells (LSECs) and liver fibrogenesis. Autophagy regulates the degradation of nuclear components, called nucleophagy, in response to damage. However, little is known about the role of nucleophagy in LSEC defenestration. Herein, we aim to dissect the underlying mechanism of progerin and nucleophagy in LSEC phenotype. We found an abnormal accumulation of progerin and a loss of SIRT1 in the nucleus of intrahepatic cells in human fibrotic liver tissue. In vivo, nuclear progerin abnormally accumulated in defenestrated LSECs, along with a depletion of SIRT1 and Cav-1 during liver fibrogenesis, whereas these effects were reversed by the overexpression of SIRT1 with the adenovirus vector. In vitro, H₂O₂ induced the excessive accumulation of progeirn, with the depletion of Lamin B1 and Cav-1 to aggravate LSEC defenestration. NAC and mito-TEMPO, classical antioxidants, inhibited NOX2- and NOX4-dependent oxidative stress to improve the depletion of Lamin B1 and Cav-1 and promoted progerin-related nucleophagy, leading to a reverse in H₂O₂-induced LSEC defenestration. However, rapamycin aggravated the H₂O₂-induced depletion of Lamin B1 and Cav-1 due to excessive autophagy, despite promoting progerin nucleophagic degradation. In addition, overexpressing SIRT1 with the adenovirus vector inhibited oxidative stress to rescue the production of Lamin B1 and Cav-1. Moreover, the SIRT1-mediated deacetylation of nuclear LC3 promoted progerin nucleophagic degradation and subsequently inhibited the degradation of Lamin B1 and Cav-1, as well as improved F-actin remodeling, contributing to maintaining LSEC fenestrae. Hence, our findings indicate a new strategy for reversing LSEC defenestration by promoting progerin clearance via the SIRT1-mediated deacetylation of nuclear LC3.

Caveolin-1 scaffolding domain peptide abrogates autophagy dysregulation in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common and fatal form of interstitial lung disease. IPF is characterized by irreversible scarring of the lungs leading to lung function decline. Although the etiology remains poorly understood, dysregulated autophagy in alveolar-epithelial cells (AECs) together with interplay between apoptotic-AECs and proliferative-myofibroblasts have been strongly implicated in IPF pathogenesis. Recent studies have revealed that a caveolin-1-derived 7-mer peptide, CSP7, mitigates established PF at least in part by improving AEC viability. In the present study, we aimed to determine whether and how CSP7 regulates autophagy in fibrotic-lung AECs. We found that p53 and autophagic proteins were markedly upregulated in AECs from mice with single/multi-doses of bleomycin—or silica-induced PF. This was abolished following treatment of PF-mice with CSP7. Further, CSP7 abrogated silica- or bleomycin-induced p53 and autophagy proteins in AECs. Immunoprecipitation further revealed that CSP7 abolishes the interaction of caveolin-1 with LC3BII and p62 in AECs. AEC-specific p53-knockout mice resisted silica- or bleomycin-induced changes in autophagy proteins, or CSP7 treatment. Our findings provide a novel mechanism by which CSP7 inhibits dysregulated autophagy in injured AECs and mitigates existing PF. These results affirm the potential of CSP7 for treating established PF, including IPF and silicosis.

Icariside Ⅱ Attenuates Palmitic Acid-Induced Endothelial Dysfunction Through SRPK1-Akt-eNOS Signaling Pathway

Background: Endothelial dysfunction is commonly accompanied by a reduced capacity for nitric oxide (NO) production and decreased NO sensitivity, playing a central role in numerous vascular diseases. Saturated free fatty acids are known to reduce NO production and then induce endothelial dysfunction. Alternative splicing participates in the regulation of cellular and tissular homeostasis and is highly regulated by serine-arginine protein kinase (SRPK1). The role of SRPK1 in the biology of endothelial cells remains elusive. Icariside Ⅱ (ICA Ⅱ) has been reported to have protective effects on endothelial function. However, the specific molecular mechanisms are still unknown. The purpose of this study is to explore the role of SRPK1 in the biology of endothelial cells and the underlying mechanism of ICA Ⅱ on palmitic acid (PA) induced endothelial dysfunction.

Methods: Endothelial dysfunction was induced using PA in human umbilical vein endothelial cells (HUVECs). The expression and phosphorylation of related proteins in the SRPK1-Akt-eNOS signaling pathway were detected by Western Blot. Cell Counting Kit-8 assay and Ki-67 immunofluorescence were used to estimate cell viability. Endothelial cell function was assessed by detecting NO production using DAF-FM DA. Interaction between ICA Ⅱ and SRPK1 was demonstrated by a biotinylated protein interaction pull-down assay.

Results: The expressions of eNOS, Akt, and SRPK1 were down-regulated in the endothelial dysfunction stimulated by PA. SRPK1 inhibitor SPHINX31 restrained endothelial cell viability in a dose-dependent manner. Moreover, inhibition of SRPK1 using SPHINX31 and knockdown of SRPK1 by shRNA also showed a down-regulation of the proteins associated with the SRPK1-Akt-eNOS signaling pathway. Biotinylated protein interaction pull-down assay revealed that ICA Ⅱ could be directly bound with SRPK1. On the other hand, ICA Ⅱ could attenuate the PA-induced endothelial dysfunction and restore cell viability through the SRPK1-Akt-eNOS pathway.

Conclusions: ICA Ⅱ, bound with SRPK1, could attenuate the endothelial dysfunction induced by the PA in HUVECs via the SRPK1-Akt-eNOS signaling pathway.

Caveolin-1 Alleviates Crohn's Disease-induced Intestinal Fibrosis by Inhibiting Fibroblasts Autophagy Through Modulating Sequestosome 1

BACKGROUND

Intestinal fibrosis is a common complication of Crohn's disease (CD) and is characterized by the excessive accumulation of extracellular matrix produced by activated myofibroblasts. Caveolin-1 (CAV1) inhibits fibrosis. However, limited data show that CAV1 affects intestinal fibrosis.

METHODS

Human CD tissue samples were gained from patients with CD who underwent surgical resection of the intestine and were defined as stenotic or nonstenotic areas. A dextran sodium sulfate-induced mouse model of intestinal fibrosis was established. For in vitro experiments, we purchased CCD-18Co intestinal fibrosis cells and isolated and cultured human primary colonic fibroblasts. These fibroblasts were activated by transforming growth factor β administration for 48 hours. In the functional experiments, a specific small interfering RNA or overexpression plasmid was transfected into fibroblasts. The messenger RNA levels of fibrosis markers, such as α-smooth muscle actin, fibronectin, connective tissue growth factor, and collagen I1α, were determined using quantitative polymerase chain reaction. Western blot analysis was applied to detect the expression of CAV1, SQSTM1/p62 (sequestosome 1), and other fibrosis markers.

RESULTS

In human CD samples and the dextran sodium sulfate-induced mouse model of intestinal fibrosis, we observed a downregulation of CAV1 in fibrosis-activated areas. Mechanistically, CAV1 knockdown in both human primary colonic fibroblasts and CCD-18Co cells promoted fibroblast activation, while CAV1 overexpression inhibited fibroblast activation in vitro. We found that SQSTM1/p62 positively correlated with CAV1 expression levels in patients with CD and that it was indirectly modulated by CAV1 expression. Rescue experiments showed that CAV1 decreased primary human intestinal fibroblast activation by inhibiting fibroblast autophagy through the modulation of SQSTM1/p62.

CONCLUSIONS

Our data demonstrate that CAV1 deficiency induces fibroblast activation by indirectly regulating SQSTM1/p62 to promote fibroblast autophagy. CAV1 or SQSTM1/p62 may be potential therapeutic targets for intestinal fibrosis.

The regulatory role and mechanism of autophagy in energy metabolism-related hepatic fibrosis

Hepatic fibrosis is a key pathological process of chronic liver diseases, caused by alcohol, toxic and aberrant energy metabolism. It progresses to cirrhosis or even hepatic carcinoma without effective treatment. Studies have shown that autophagy has important regulatory effects on hepatic stellate cells (HSCs) energy metabolism, and then affect the activation state of HSCs. Autophagy maintains hepatic energy homeostasis, and the dysregulation of autophagy can lead to the activation of HSCs and the occurrence and development of hepatic fibrosis. It is necessary to explore the mechanism of autophagy in energy metabolism-related hepatic fibrosis. Herein, the current study summarizes the regulating mechanisms of autophagy through different targets and signal pathways in energy metabolism-related hepatic fibrosis, and discusses the regulatory effect of autophagy by natural plant-derived, endogenous and synthetic compounds for the treatment of hepatic fibrosis. A better comprehension of autophagy in hepatic stellate cells energy metabolism-related hepatic fibrosis may provide effective intervention of hepatic fibrosis, explore the potential clinical strategies and promote the drug treatment of hepatic fibrosis.

The Hepatic Sinusoid in Chronic Liver Disease: The Optimal Milieu for Cancer

Simple Summary

During the development of chronic liver disease, the hepatic sinusoid undergoes major changes that further compromise the hepatic function, inducing persistent inflammation and the formation of scar tissue, together with alterations in liver hemodynamics. This diseased background may induce the formation and development of hepatocellular carcinoma (HCC), which is the most common form of primary liver cancer and a major cause of mortality. In this review, we describe the ways in which the dysregulation of hepatic sinusoidal cells—including liver sinusoidal cells, Kupffer cells, and hepatic stellate cells—may have an important role in the development of HCC. Our review summarizes all of the known sinusoidal processes in both health and disease, and possible treatments focusing on the dysregulation of the sinusoid; finally, we discuss how some of these alterations occurring during chronic injury are shared with the pathology of HCC and may contribute to its development.

Abstract

The liver sinusoids are a unique type of microvascular beds. The specialized phenotype of sinusoidal cells is essential for their communication, and for the function of all hepatic cell types, including hepatocytes. Liver sinusoidal endothelial cells (LSECs) conform the inner layer of the sinusoids, which is permeable due to the fenestrae across the cytoplasm; hepatic stellate cells (HSCs) surround LSECs, regulate the vascular tone, and synthetize the extracellular matrix, and Kupffer cells (KCs) are the liver-resident macrophages. Upon injury, the harmonic equilibrium in sinusoidal communication is disrupted, leading to phenotypic alterations that may affect the function of the whole liver if the damage persists. Understanding how the specialized sinusoidal cells work in coordination with each other in healthy livers and chronic liver disease is of the utmost importance for the discovery of new therapeutic targets and the design of novel pharmacological strategies. In this manuscript, we summarize the current knowledge on the role of sinusoidal cells and their communication both in health and chronic liver diseases, and their potential pharmacologic modulation. Finally, we discuss how alterations occurring during chronic injury may contribute to the development of hepatocellular carcinoma, which is usually developed in the background of chronic liver disease.

Klotho as Potential Autophagy Regulator and Therapeutic Target

The protein Klotho can significantly delay aging, so it has attracted widespread attention. Abnormal downregulation of Klotho has been detected in several aging-related diseases, such as Alzheimer’s disease, kidney injury, cancer, chronic obstructive pulmonary disease (COPD), vascular disease, muscular dystrophy and diabetes. Conversely, many exogenous and endogenous factors, several drugs, lifestyle changes and genetic manipulations were reported to exert therapeutic effects through increasing Klotho expression. In recent years, Klotho has been identified as a potential autophagy regulator. How Klotho may contribute to reversing the effects of aging and disease became clearer when it was linked to autophagy, the process in which eukaryotic cells clear away dysfunctional proteins and damaged organelles: the abovementioned diseases involve abnormal autophagy. Interestingly, growing evidence indicates that Klotho plays a dual role as inducer or inhibitor of autophagy in different physiological or pathological conditions through its influence on IGF-1/PI3K/Akt/mTOR signaling pathway, Beclin 1 expression and activity, as well as aldosterone level, which can help restore autophagy to beneficial levels. The present review examines the role of Klotho in regulating autophagy in Alzheimer’s disease, kidney injury, cancer, COPD, vascular disease, muscular dystrophy and diabetes. Targeting Klotho may provide a new perspective for preventing and treating aging-related diseases.

Sirtuin 1 ameliorates defenestration in hepatic sinusoidal endothelial cells during liver fibrosis via inhibiting stress-induced premature senescence

OBJECTIVE

Premature senescence is related to progerin and involves in endothelial dysfunction and liver diseases. Activating sirtuin 1 (SIRT1) ameliorates liver fibrosis. However, the mechanisms of premature senescence in defenestration of hepatic sinusoidal endothelial cells (HSECs) and how SIRT1 affects HSECs fenestrae remain elusive.

METHODS

We employed the CCl4 -induced liver fibrogenesis rat models and cultured primary HSECs in vitro, administered with the SIRT1-adenovirus vector, the activator of SIRT1 and knockdown NOX2. We measured the activity of senescence-associated β-galactosidase (SA-β-gal) in HSECs. Meanwhile, the protein expression of SIRT1, NOX2, progerin, Lamin A/C, Ac p53 K381 and total p53 was detected by Western blot, co-immunoprecipitation and immunofluorescence.

RESULTS

In vivo, premature senescence was triggered by oxidative stress during CCl4 -induced HSECs defenestration and liver fibrogenesis, whereas overexpressing SIRT1 with adenovirus vector lessened premature senescence to relieve CCl4 -induced HSECs defenestration and liver fibrosis. In vitro, HSECs fenestrae disappeared, with emerging progerin-associated premature senescence; these effects were aggravated by H2 O2 . Nevertheless, knockdown of NOX2, activation of SIRT1 with resveratrol and SIRT1-adenovirus vector inhibited progerin-associated premature senescence to maintain fenestrae through deacetylating p53. Furthermore, more Ac p53 K381 and progerin co-localized with the abnormal accumulation of actin filament (F-actin) in the nuclear envelope of H2 O2 -treated HSECs; in contrast, these effects were rescued by overexpressing SIRT1.

CONCLUSION

SIRT1-mediated deacetylation maintains HSECs fenestrae and attenuates liver fibrogenesis through inhibiting oxidative stress-induced premature senescence.

Aldosterone enhances high phosphate-induced vascular calcification through inhibition of AMPK-mediated autophagy

It remains unclear whether the necessity of calcified mellitus induced by high inorganic phosphate (Pi) is required and the roles of autophagy plays in aldosterone (Aldo)‐enhanced vascular calcification (VC) and vascular smooth muscle cell (VSMC) osteogenic differentiation. In the present study, we found that Aldo enhanced VC both in vivo and in vitro only in the presence of high Pi, alongside with increased expression of VSMC osteogenic proteins (BMP2, Runx2 and OCN) and decreased expression of VSMC contractile proteins (α‐SMA, SM22α and smoothelin). However, these effects were blocked by mineralocorticoid receptor inhibitor, spironolactone. In addition, the stimulatory effects of Aldo on VSMC calcification were further accelerated by the autophagy inhibitor, 3‐MA, and were counteracted by the autophagy inducer, rapamycin. Moreover, inhibiting adenosine monophosphate‐activated protein kinase (AMPK) by Compound C attenuated Aldo/MR‐enhanced VC. These results suggested that Aldo facilitates high Pi‐induced VSMC osteogenic phenotypic switch and calcification through MR‐mediated signalling pathways that involve AMPK‐dependent autophagy, which provided new insights into Aldo excess‐associated VC in various settings.

Alamandine attenuates hepatic fibrosis by regulating autophagy induced by NOX4-dependent ROS

Angiotensin II (Ang II) has been reported to aggravate hepatic fibrosis by inducing NADPH oxidase (NOX)-dependent oxidative stress. Alamandine (ALA) protects against fibrosis by counteracting Ang II via the MAS-related G-protein coupled (MrgD) receptor, though the effects of alamandine on hepatic fibrosis remain unknown. Autophagy activated by reactive oxygen species (ROS) is a novel mechanism of hepatic fibrosis. However, whether autophagy is involved in the regulation of Ang II-induced hepatic fibrosis still requires investigation. We explored the effect of alamandine on hepatic fibrosis via regulation of autophagy by redox balance modulation. In vivo, alamandine reduced CCl4-induced hepatic fibrosis, hydrogen peroxide (H2O2) content, protein levels of NOX4 and autophagy impairment. In vitro, Ang II treatment elevated NOX4 protein expression and ROS production along with up-regulation of the angiotensin converting enzyme (ACE)/Ang II/Ang II type 1 receptor (AT1R) axis. These changes resulted in the accumulation of impaired autophagosomes in hepatic stellate cells (HSCs). Treatment with NOX4 inhibitor VAS2870, ROS scavenger N-acetylcysteine (NAC), and NOX4 small interfering RNA (siRNA) inhibited Ang II-induced autophagy and collagen synthesis. Alamandine shifted the balance of renin-angiotensin system (RAS) toward the angiotensin converting enzyme 2 (ACE2)/alamandine/MrgD axis, and inhibited both Ang II-induced ROS and autophagy activation, leading to attenuation of HSCs migration or collagen synthesis. In summary, alamandine attenuated liver fibrosis by regulating autophagy induced by NOX4-dependent ROS.

Twist1-induced miR-199a-3p promotes liver fibrosis by suppressing caveolin-2 and activating TGF-β pathway

The activation of hepatic stellate cells (HSCs) participates in liver fibrosis, and emerging evidences indicate that microRNAs (miRNAs) are abnormally expressed during HSC activation. However, the potential roles of miRNAs in liver fibrosis still remain elusive. Therefore, this study aimed to investigate the role of miR-199a-3p in liver fibrosis and its underlying mechanism. We found that miR-199a-3p expression was dramatically upregulated during HSC activation in vitro, and during liver fibrogenesis in CCl₄-treated rats, and its liver expression was increased in the patients with cirrhosis. By the luciferase assay and RT-qPCR, we revealed that the expression of miR-199a-3p in HSCs was driven by the transcription factor Twist1 which could be further induced by TGF-β treatment. Functional studies showed that inhibition of miR-199a-3p in both human LX2 cells and rat HSCs significantly decreased the expression of fibrotic markers, such as fibronectin and connective tissue growth factor (CTGF), whereas the forced expression of miR-199a-3p exhibited opposite effects, demonstrating the role of miR-199a-3p in promoting HSC activation. Mechanistically, miR-199a-3p plays an important role in TGF-β signalling pathway activation through targeting CAV2 that negatively regulates the expression of transforming growth factor-beta receptor type I (TGFβRI). Importantly, administration of antagomiR-199a-3p in the CCl₄-treated mice significantly ameliorated hepatic fibrosis. In conclusion, Twist1-induced miR-199a-3p mediates the activation of HSCs by suppressing CAV2 expression and subsequently increasing TGFβRI expression to promote TGF-β pathway. Our findings highlight the therapeutic potential of miR-199a-3p for hepatic fibrosis.

Non-caveolar caveolins – duties outside the caves

Caveolae are invaginations of the plasma membrane that are remarkably abundant in adipocytes, endothelial cells and muscle. Caveolae provide cells with resources for mechanoprotection, can undergo fission from the plasma membrane and can regulate a variety of signaling pathways. Caveolins are fundamental components of caveolae, but many cells, such as hepatocytes and many neurons, express caveolins without forming distinguishable caveolae. Thus, the function of caveolins goes beyond their roles as caveolar components. The membrane-organizing and -sculpting capacities of caveolins, in combination with their complex intracellular trafficking, might contribute to these additional roles. Furthermore, non-caveolar caveolins can potentially interact with proteins normally excluded from caveolae. Here, we revisit the non-canonical roles of caveolins in a variety of cellular contexts including liver, brain, lymphocytes, cilia and cancer cells, as well as consider insights from invertebrate systems. Non-caveolar caveolins can determine the intracellular fluxes of active lipids, including cholesterol and sphingolipids. Accordingly, caveolins directly or remotely control a plethora of lipid-dependent processes such as the endocytosis of specific cargoes, sorting and transport in endocytic compartments, or different signaling pathways. Indeed, loss-of-function of non-caveolar caveolins might contribute to the common phenotypes and pathologies of caveolin-deficient cells and animals.

Hepatocyte caveolin-1 modulates metabolic gene profiles and functions in non-alcoholic fatty liver disease

Caveolin-1 (CAV1) is a crucial regulator of lipid accumulation and metabolism. Previous studies have shown that global Cav1 deficiency affects lipid metabolism and hepatic steatosis. We aimed to analyze the consequences of hepatocyte-specific Cav1 knockout under healthy conditions and upon non-alcoholic fatty liver disease (NAFLD) development. Male and female hepatocyte-specific Cav1 knockout (HepCAV1ko) mice were fed a methionine/choline (MCD) deficient diet for 4 weeks. MCD feeding caused severe hepatic steatosis and slight fibrosis. In addition, liver function parameters, i.e., ALT, AST, and GLDH, were elevated, while cholesterol and glucose level were reduced upon MCD feeding. These differences were not affected by hepatocyte-specific Cav1 knockout. Microarray analysis showed strong differences in gene expression profiles of livers from HepCAV1ko mice compared those of global Cav1 knockout animals. Pathway enrichment analysis identified that metabolic alterations were sex-dimorphically regulated by hepatocyte-specific CAV1. In male HepCAV1ko mice, metabolic pathways were suppressed in NAFLD, whereas in female knockout mice induced. Moreover, gender-specific transcription profiles were modulated in healthy animals. In conclusion, our results demonstrate that hepatocyte-specific Cav1 knockout significantly altered gene profiles, did not affect liver steatosis and fibrosis in NAFLD and that gender had severe impact on gene expression patterns in healthy and diseased hepatocyte-specific Cav1 knockout mice.

Critical role of caveolin-1 in aflatoxin B1-induced hepatotoxicity via the regulation of oxidation and autophagy

Aflatoxin B1 (AFB1) is a potent hepatocarcinogen in humans and exposure to AFB1 is known to cause both acute and chronic hepatocellular injury. As the liver is known to be the main target organ of aflatoxin, it is important to identify the key molecules that participate in AFB1-induced hepatotoxicity and to investigate their underlying mechanisms. In this study, the critical role of caveolin-1 in AFB1-induced hepatic cell apoptosis was examined. We found a decrease in cell viability and an increase in oxidation and apoptosis in human hepatocyte L02 cells after AFB1 exposure. In addition, the intracellular expression of caveolin-1 was increased in response to AFB1 treatment. Downregulation of caveolin-1 significantly alleviated AFB1-induced apoptosis and decreased cell viability, whereas overexpression of caveolin-1 reversed these effects. Further functional analysis showed that caveolin-1 participates in AFB1-induced oxidative stress through its interaction with Nrf2, leading to the downregulation of cellular antioxidant enzymes and the promotion of oxidative stress-induced apoptosis. In addition, caveolin-1 was found to regulate AFB1-induced autophagy. This finding was supported by the effect that caveolin-1 deficiency promoted autophagy after AFB1 treatment, leading to the inhibition of apoptosis, whereas overexpression of caveolin-1 inhibited autophagy and accelerated apoptosis. Interestingly, further investigation showed that caveolin-1 participates in AFB1-induced autophagy by regulating the EGFR/PI3K-AKT/mTOR signaling pathway. Taken together, our data reveal that caveolin-1 plays a crucial role in AFB1-induced hepatic cell apoptosis via the regulation of oxidation and autophagy, which provides a potential target for the development of novel treatments to combat AFB1 hepatotoxicity.

Aldosterone Rapidly Enhances Levels of the Striatin and Caveolin-1 Proteins in Rat Kidney: The Role of the Mineralocorticoid Receptor

BACKGROUND

Striatin and caveolin-1 (cav-1) are scaffolding/regulating proteins that are associated with salt-sensitive high blood pressure and promote renal sodium and water reabsorption, respectively. The mineralocorticoid receptor (MR) interacts with striatin and cav-1, while aldosterone increases striatin and cav-1 levels. However, no in vivo data have been reported for the levels of these proteins in the kidney.

METHODS

Male Wistar rats were intraperitoneally injected with normal saline solution, aldosterone alone (Aldo: 150 μg/kg body weight), or aldosterone after pretreatment with eplerenone, an MR blocker, 30 minutes before the aldosterone injection (eplerenone [Ep.]+Aldo). Thirty minutes after the aldosterone injection, the amount and localization of striatin and cav-1 were determined by Western blot analysis and immunohistochemistry, respectively.

RESULTS

Aldosterone increased striatin levels by 150% (P<0.05), and cav-1 levels by 200% (P<0.001). Eplerenone had no significant effect on striatin levels, but partially blocked the aldosterone-induced increase in cav-1 levels. Aldosterone stimulated striatin and cav-1 immunoreactivity in both the cortex and medulla. Eplerenone reduced cav-1 immunostaining in both areas; however, striatin intensity was reduced in the cortex, but increased in the medulla.

CONCLUSION

This is the first in vivo study demonstrating that aldosterone rapidly enhances renal levels of striatin and cav-1. Aldosterone increases striatin levels via an MR-independent pathway, whereas cav-1 is partially regulated through MR.

The Reactive Oxygen Species-Mitophagy Signaling Pathway Regulates Liver Endothelial Cell Survival During Ischemia/Reperfusion Injury

Ischemia/reperfusion injury (IRI) is the main cause of complications following liver transplantation. Reactive oxygen species (ROS) were thought to be the main regulators of IRI. However, recent studies demonstrate that ROS activate the cytoprotective mechanism of autophagy promoting cell survival. Liver IRI initially damages the liver endothelial cells (LEC), but whether ROS-autophagy promotes cell survival in LEC during IRI is not known. Primary human LEC were isolated from human liver tissue and exposed to an in vitro model of IRI to assess the role of autophagy in LEC. The role of autophagy during liver IRI in vivo was assessed using a murine model of partial liver IRI. During IRI, ROS specifically activate autophagy-related protein (ATG) 7 promoting autophagic flux and the formation of LC3B-positive puncta around mitochondria in primary human LEC. Inhibition of ROS reduces autophagic flux in LEC during IRI inducing necrosis. In addition, small interfering RNA knockdown of ATG7 sensitized LEC to necrosis during IRI. In vivo murine livers in uninjured liver lobes demonstrate autophagy within LEC that is reduced following IRI with concomitant reduction in autophagic flux and increased cell death. In conclusion, these findings demonstrate that during liver IRI ROS-dependent autophagy promotes the survival of LEC, and therapeutic targeting of this signaling pathway may reduce liver IRI following transplantation.

Autophagic degradation of caveolin-1 promotes liver sinusoidal endothelial cells defenestration

Autophagy, interacting with actin cytoskeleton and the NO-dependent pathway, may affect the phenotype and function of endothelial cells. Moreover, caveolin-1 (Cav-1), as a structure protein in liver sinusoidal endothelial cells (LSECs), is closely related to autophagy. Hence, we aim to explore the role of autophagic degradation of Cav-1 in LSECs defenestration. In vivo, we found the increase of autophagy in liver sinusoidal endothelium in human fibrotic liver. Furthermore, autophagy, degradation of Cav-1, and actin filament (F-actin) remodeling were triggered during the process of CCl4-induced LSECs defenestration; in contrast, autophagy inhibitor 3MA diminished the degradation of Cav-1 to maintain fenestrae and relieve CCl4-induced fibrosis. In vitro, during LSECs defenestration, the NO-dependent pathway was down-regulated through the reduction of the PI3K–AKT–MTOR pathway and initiation of autophagic degradation of Cav-1; while, these effects were aggravated by starvation. However, VEGF inhibited autophagic degradation of Cav-1 and F-actin remodeling to maintain LSECs fenestrae via activating the PI3K–AKT–MTOR pathway. Additionally, inhibiting autophagy, such as 3MA, bafilomycin, or ATG5-siRNA, could attenuate the depletion of Cav-1 and F-actin remodeling to maintain LSECs fenestrae and improve the NO-dependent pathway; in turn, eNOS-siRNA and L-NAME, for blocking the NO-dependent pathway, could elevate autophagic degradation of Cav-1 to aggravate defenestration. Finally, overexpressed Cav-1 rescued rapamycin-induced autophagic degradation of Cav-1 to maintain LSECs fenestrae; whereas knockdown of Cav-1 facilitated defenestration due to the activation of the AMPK-dependent autophagy. Consequently, autophagic degradation of Cav-1 promotes LSECs defenestration via inhibiting the NO-dependent pathway and F-actin remodeling.