Defective Protein Catabolism in Atherosclerotic Vascular Inflammation

Calpain and Cardiometabolic Diseases

Calpain is defined as a member of the superfamily of cysteine proteases possessing the CysPC motif within the gene. Calpain-1 and -2, which are categorized as conventional isozymes, execute limited proteolysis in a calcium-dependent fashion. Accordingly, the calpain system participates in physiological and pathological phenomena, including cell migration, apoptosis, and synaptic plasticity. Recent investigations have unveiled the contributions of both conventional and unconventional calpains to the pathogenesis of cardiometabolic disorders. In the context of atherosclerosis, overactivation of conventional calpain attenuates the barrier function of vascular endothelial cells and decreases the immunosuppressive effects attributed to lymphatic endothelial cells. In addition, calpain-6 induces aberrant mRNA splicing in macrophages, conferring atheroprone properties. In terms of diabetes, polymorphisms of the calpain-10 gene can modify insulin secretion and glucose disposal. Moreover, conventional calpain reportedly participates in amino acid production from vascular endothelial cells to induce alteration of amino acid composition in the liver microenvironment, thereby facilitating steatohepatitis. Such multifaceted functionality of calpain underscores its potential as a promising candidate for pharmaceutical targets for the treatment of cardiometabolic diseases. Consequently, the present review highlights the pivotal role of calpains in the complications of cardiometabolic diseases and embarks upon a characterization of calpains as molecular targets.

Calpain-mediated proteolytic production of free amino acids in vascular endothelial cells augments obesity-induced hepatic steatosis

Free amino acids that accumulate in the plasma of diabetes and obesity patients influence lipid metabolism and protein synthesis in the liver. The stress-inducible intracellular protease calpain proteolyzes various substrates in vascular endothelial cells (ECs), although its contribution to the supply of free amino acids in the liver microenvironment remains enigmatic. In the present study, we showed that calpains are associated with free amino acid production in cultured ECs. Furthermore, conditioned media derived from calpain-activated ECs facilitated the phosphorylation of ribosomal protein S6 kinase (S6K) and de novo lipogenesis in hepatocytes, which were abolished by the amino acid transporter inhibitor, JPH203, and the mTORC1 inhibitor, rapamycin. Meanwhile, calpain-overexpressing capillary-like ECs were observed in the livers of high-fat diet-fed mice. Conditional knockout of EC/hematopoietic Capns1, which encodes a calpain regulatory subunit, diminished levels of branched chain amino acids in the hepatic microenvironment without altering plasma amino acid levels. Concomitantly, conditional knockout of Capns1 mitigated hepatic steatosis without normalizing body weight and the plasma lipoprotein profile in an amino acid transporter-dependent manner. Mice with targeted Capns1 knockout exhibited reduced phosphorylation of S6K and maturation of lipid homeostasis transcription factor SREBP1 in hepatocytes. Finally, we show that bone marrow transplantation negated the contribution of hematopoietic calpain systems; therefore, calpains are likely responsible for the observed phenotypes of ECs. We conclude that overactivation of calpain systems may be responsible for the production of free amino acid in ECs, which may be sufficient to potentiate S6K/SREBP1-induced lipogenesis in surrounding hepatocytes.

New insight into biology, molecular diagnostics and treatment options of unstable carotid atherosclerotic plaque: a narrative review

Indications for intervention in hemodynamically relevant carotid artery stenosis (carotid endarterectomy or stenting) are primarily based on a degree of stenosis and symptomatology. To date the plaque vulnerability is rarely taken into account in clinical decision making although development of molecular imaging allows a better understanding of plaque biology and provides new techniques detecting potentially vulnerable plaque at risk. A significant number of reports describing the mechanisms of unstable plaque formation suggest that it is a multifactorial process. Inflammation, lipid accumulation, apoptosis, proteolysis, the thrombotic process and angiogenesis are among the main factors of carotid plaque destabilization. Although inflammation is a key process in development of plaque vulnerability, the hemostasis and neoangiogenesis should be regarded as equally important. Only a small group of asymptomatic patients may benefit from the invasive treatment and it remains a challenge to determine whether initially asymptomatic carotid plaque become unstable or vulnerable. Currently, the main task of research on atherosclerotic lesion imaging is focused on functional state of the plaque. The presence of one or more features such as stenosis progression, large plaque area, large juxta-luminal black area, plaque echolucency, intra-plaque hemorrhage, impaired cerebral vascular reserve and spontaneous embolization may indicate patients at higher risk for stroke suitable for revascularization. Treatment of carotid stenosis as one of the manifestations of generalized atherosclerosis requires a broad approach. Nowadays pharmacological treatment options for the atherosclerotic process are largely aimed at stimulating the plaque stabilization, but in symptomatic patients and selected asymptomatic patients, carotid plaque should be removed as a potential source of embolism.

Impaired lipophagy in endothelial cells with prolonged exposure to oxidized low‑density lipoprotein

Oxidative stress induces the formation of oxidized low-density lipoprotein (ox-LDL), which accelerates the development of atherosclerosis and the rupture of atherosclerotic plaques by promoting lipid accumulation and inhibiting autophagy in vascular cells. Lipophagy is known to be involved in maintaining the balance of neutral lipid metabolism; however, the phenomenon of lipophagy deficiency in ox-LDL-treated endothelial cells (ECs) remains to be elucidated. It has been demonstrated that lipid accumulation caused by ox-LDL inhibits autophagy, which promotes apoptosis in ECs. The aim of the present study was to investigate the association between decreased autophagy and lipid accumulation in ECs treated with ox-LDL. Electron microscopy demonstrated that the formation of autolipophagosomes was decreased in ox-LDL-treated human umbilical vein ECs compared with that in the LDL-treated group and was accompanied by a decrease in the autophagy-associated proteins via western blotting analysis. Using laser focal colocalization detection, decreased lipid processing was observed in the lysosomes of ox-LDL-treated ECs, which indicated that lipophagy may be attenuated and subsequently result in lipid accumulation in ox-LDL-treated ECs.

Calpain proteolytic systems counteract endothelial cell adaptation to inflammatory environments

Vascular endothelial cells (ECs) make up the innermost surface of arteries, veins, and capillaries, separating the remaining layers of the vessel wall from circulating blood. Under non-inflammatory conditions, ECs are quiescent and form a robust barrier structure; however, exposure to inflammatory stimuli induces changes in the expression of EC proteins that control transcellular permeability and facilitate angiogenic tube formation. Increasing evidence suggests that dysfunction in intracellular proteolytic systems disturbs EC adaptation to the inflammatory environment, leading to vascular disorders such as atherosclerosis and pathological angiogenesis. Recent work has highlighted the contribution of the calpain–calpastatin stress-responsive intracellular proteolytic system to adaptation failure in ECs. In this review, we summarize our current knowledge of calpain–calpastatin-mediated physiologic and pathogenic regulation in ECs and discuss the molecular basis by which disruption of this system perturbs EC adaptation to the inflammatory environment.

Methylomic Changes of Autophagy-Related Genes by Legionella Effector Lpg2936 in Infected Macrophages

Legionella pneumophila (L. pneumophila) is a Gram-negative bacterium that infects the human respiratory tract causing Legionnaires' disease, a severe form of pneumonia. Recently, rising evidence indicated the ability of Legionella to regulate host defense via its type 4 secretion system including hundreds of effectors that promote intracellular bacterial replication. The host defense against such invaders includes autophagic machinery that is responsible for degradation events of invading pathogens and recycling of cell components. The interplay between host autophagy and Legionella infection has been reported, indicating the role of bacterial effectors in the regulation of autophagy during intracellular replication. Here, we investigated the potential impact of Legionella effector Lpg2936 in the regulation of host autophagy and its role in bacterial replication using mice-derived macrophages and human lung epithelial cells (A549 cells). First, monitoring of autophagic flux following infection revealed a marked reduction of Atg7 and LC3B expression profile and low accumulation levels of autophagy-related LC3-I, LC3-II, and the Atg12-Atg5 protein complex. A novel methyladenine alteration was observed due to irreversible changes of GATC motif to G(6 mA) TC in the promoter region of Atg7 and LC3B indicated by cleaved genomic-DNA using the N6 methyladenine-sensitive restriction enzyme DpnI. Interestingly, RNA interference (RNAi) of Lpg2936 in infected macrophages showed dramatic inhibition of bacterial replication by restoring the expression of autophagy-related proteins. This is accompanied by low production levels of bacterial-associated pro-inflammatory cytokines. Furthermore, a constructed Lpg2936 segment in the GFP expression vector was translocated in the host nucleus and successfully induced methyladenine changes in Atg7 and LC3B promoter region and subsequently regulated autophagy in A549 cells independent of infection. Finally, treatment with methylation inhibitors 5-AZA and (2)-Epigallocatechin-3-gallate (EGCG) was able to restore autophagy-related gene expression and to disrupt bacterial replication in infected macrophages. This cumulative evidence indicates the methylation effect of Legionella effector Lpg2936 on the host autophagy-related molecules Atg7 and LC3B and subsequent reduction in the expression levels of autophagy effectors during intracellular replication of L. pneumophila.

Endothelial calpain systems orchestrate myofibroblast differentiation during wound healing

The transformation of fibroblasts to myofibroblasts plays a major role in fibrogenic responses during dermal wound healing. We show a contribution of calpain systems (intracellular regulatory protease systems) in vascular endothelial cells (ECs) to myofibroblast differentiation in wound sites. Dermal wound healing experiments in mice found that calpastatin (an endogenous inhibitor of calpains) is enriched in preexisting vessels but not in newly formed capillaries. Transgenic overexpression of calpastatin in ECs delayed wound healing in mice as well as reducing the keratinocyte layer, extracellular matrix deposition, and myofibroblast accumulation in wound sites. EC and leukocyte markers, however, remain unchanged. Calpastatin overexpression reduced the expression of genes encoding platelet-derived growth factor-B and PDGF receptor-β (PDGFR-β). Topical application of platelet-derived growth factor-BB-containing ointment to wounds accelerated healing in control mice, but calpastatin overexpression prevented this acceleration. In cultured human dermal fibroblasts, α-smooth muscle actin and PDGFR-β were up-regulated by coculturing with ECs, but this action was inhibited by suppression of EC calpain activity. EC-driven transformation of mouse dermal fibroblasts was also suppressed by calpastatin overexpression in ECs. These results suggest that endothelial calpain systems influence PDGFR-β signaling in fibroblasts, EC-driven myofibroblast differentiation, and subsequent fibrogenic responses in wounds.-Miyazaki, T., Haraguchi, S., Kim-Kaneyama, J.-R., Miyazaki, A. Endothelial calpain systems orchestrate myofibroblast differentiation during wound healing.