Calpain inhibition attenuates angiotensin II-induced abdominal aortic aneurysms and atherosclerosis in low-density lipoprotein receptor-deficient mice

Advanced glycation end products promote the progression of chronic kidney diseases by targeting calpain 6

Advanced glycation end products (AGEs) are produced by glycosylation or oxidation of proteins and lipids and are tightly involved in the chronic kidney disease (CKD) process. Calpain 6 (CAPN6) is a non-classical calpain that has been reported to be overexpressed in CKD. This study aimed to explore the effects of AGEs in CKD progress and their correlation with CAPN6. AGEs production was measured using ELISA. The CCK-8 assay was used to test cell proliferation. mRNA and protein levels were tested using qRT-PCR and western blot. The progress of glycolysis was tested by calculating the ATP and ECAR content in HK-2 cells. The expression of AGEs and CAPN6 was significantly increased in patients with CKD3, CKD4, and CKD5. AGEs treatment inhibited cell proliferation and glycolysis and accelerated apoptosis. Additionally, CAPN6 knockdown effectively reversed the effects of AGEs in HK-2 cells. In addition, overexpressed CAPN6 played similar role to AGEs, which suppressed cell proliferation and glycolysis and facilitated apoptosis. Moreover, the administration of 2-DG, a glycolysis inhibitor, counteracted the effects of CAPN6 silencing in HK-2 cells. Mechanistically, CAPN6 interacts with NF-κB and PDTC reduced CAPN6 expression in HK-2 cells. This investigation revealed that AGEs facilitate CKD development in vitro by modulating the expression of CAPN6.

Celastrol Supplementation Ablates Sexual Dimorphism of Abdominal Aortic Aneurysm Formation in Mice

BACKGROUND

Abdominal aortic aneurysms (AAAs) are permanent dilations of the abdominal aorta with 4-5 times greater prevalence in males than in females. The aim of this study is to define whether Celastrol, a pentacyclic triterpene from the root extracts of Tripterygium wilfordii, supplementation influences angiotensin II (AngII)-induced AAAs in hypercholesterolemic mice.

METHODS

Age-matched (8-12 weeks old) male and female low-density lipoprotein (Ldl) receptor-deficient mice were fed a fat-enriched diet supplemented with or without Celastrol (10 mg/kg/day) for five weeks. After one week of diet feeding, mice were infused with either saline (n = 5 per group) or AngII (500 or 1000 ng/kg/min, n = 12-15 per group) for 28 days.

RESULTS

Dietary supplementation of Celastrol profoundly increased AngII-induced abdominal aortic luminal dilation and external aortic width in male mice as measured by ultrasonography and ex vivo measurement, with a significant increase in incidence compared to the control group. Celastrol supplementation in female mice resulted in significantly increased AngII-induced AAA formation and incidence. In addition, Celastrol supplementation significantly increased AngII-induced aortic medial elastin degradation accompanied by significant aortic MMP9 activation in both male and female mice compared to saline and AngII controls.

CONCLUSIONS

Celastrol supplementation to Ldl receptor-deficient mice ablates sexual dimorphism and promotes AngII-induced AAA formation, which is associated with increased MMP9 activation and aortic medial destruction.

Mechanosignals in abdominal aortic aneurysms

Cumulative evidence has shown that mechanical and frictional forces exert distinct effects in the multi-cellular aortic layers and play a significant role in the development of abdominal aortic aneurysms (AAA). These mechanical cues collectively trigger signaling cascades relying on mechanosensory cellular hubs that regulate vascular remodeling programs leading to the exaggerated degradation of the extracellular matrix (ECM), culminating in lethal aortic rupture. In this review, we provide an update and summarize the current understanding of the mechanotransduction networks in different cell types during AAA development. We focus on different mechanosensors and stressors that accumulate in the AAA sac and the mechanotransduction cascades that contribute to inflammation, oxidative stress, remodeling, and ECM degradation. We provide perspectives on manipulating this mechano-machinery as a new direction for future research in AAA.

Edaravone Attenuated Angiotensin II-Induced Atherosclerosis and Abdominal Aortic Aneurysms in Apolipoprotein E-Deficient Mice

Background: The aim of the study was to define whether edaravone, a free-radical scavenger, influenced angiotensin II (AngII)-induced atherosclerosis and abdominal aortic aneurysms (AAAs) formation. Methods: Male apolipoprotein E-deficient mice (8–12 weeks old) were fed with a normal diet for 5 weeks. Either edaravone (10 mg/kg/day) or vehicle was injected intraperitoneally for 5 weeks. After 1 week of injections, mice were infused subcutaneously with either AngII (1000 ng/kg/min, n = 16–17 per group) or saline (n = 5 per group) by osmotic minipumps for 4 weeks. Results: AngII increased systolic blood pressure equivalently in mice administered with either edaravone or saline. Edaravone had no effect on plasma total cholesterol concentrations and body weights. AngII infusion significantly increased ex vivo maximal diameters of abdominal aortas and en face atherosclerosis but was significantly attenuated by edaravone administration. Edaravone also reduced the incidence of AngII-induced AAAs. In addition, edaravone diminished AngII-induced aortic MMP-2 activation. Quantitative RT-PCR revealed that edaravone ameliorated mRNA abundance of aortic MCP-1 and IL-1β. Immunostaining demonstrated that edaravone attenuated oxidative stress and macrophage accumulation in the aorta. Furthermore, edaravone administration suppressed thioglycolate-induced mice peritoneal macrophages (MPMs) accumulation and mRNA abundance of MCP-1 in MPMs in male apolipoprotein E-deficient mice. In vitro, edaravone reduced LPS-induced mRNA abundance of MCP-1 in MPMs. Conclusions: Edaravone attenuated AngII-induced AAAs and atherosclerosis in male apolipoprotein E-deficient mice via anti-oxidative action and anti-inflammatory effect.

Calpain inhibitor prevents atherosclerosis in apolipoprotein E knockout mice by regulating mRNA expression of genes related to cholesterol uptake and efflux

PURPOSE

We previously reported that a calpain inhibitor (CAI) prevents the development of atherosclerosis in rats. This study aimed to investigate the effects of CAI (1 mg/kg) on atherosclerosis in apolipoprotein E knockout (ApoE KO) mice that were fed a high-fat diet (HFD) and explore the underlying mechanism by analyzing the expression of genes related to the uptake and efflux of cholesterol.

METHODS

Atherosclerotic plaques were evaluated. The activity of calpain in the aorta and that of superoxide dismutase (SOD) in the serum were assessed. Lipid profiles in the serum and liver were examined. Serum oxidized low-density lipoprotein (oxLDL), malondialdehyde (MDA), tumor necrosis factor (TNF-α), and interleukin-6 (IL-6) levels were measured. The mRNA expressions of CD68, TNF-α, IL-6, CD36, scavenger receptor (SR-A), peroxisome proliferator-activated receptor gamma (PPAR-γ), liver-x-receptor alpha (LXR-α), and ATP-binding cassette transporter class A1 (ABCA1) in the aorta and peritoneal macrophages were also evaluated.

RESULTS

CAI reduced calpain activity in the aorta. CAI also impeded atherosclerotic lesion formation and mRNA expression of CD68 in the aorta and peritoneal macrophages of ApoE KO mice compared with those of mice receiving HFD. However, CAI had no effect on body weight and lipid levels in both the serum and liver. CAI significantly decreased MDA, oxLDL, TNF-α, and IL-6 levels and increased SOD activity in the serum. Moreover, CAI significantly inhibited the mRNA expression of TNF-α and IL-6 genes in the aorta and peritoneal macrophages. In addition, CAI significantly downregulated the mRNA expression of scavenger receptors CD36 and SR-A and upregulated the expression of genes involved in the cholesterol efflux pathway, i.e., PPAR-γ, LXR-α, and ABCA1 in the aorta and peritoneal macrophages.

CONCLUSIONS

CAI inhibited the development of atherosclerotic lesions in ApoE KO mice, and this effect might be related to the reduction of oxidative stress and inflammation and the improvement of cholesterol intake and efflux pathways.

Inducible Depletion of Calpain-2 Mitigates Abdominal Aortic Aneurysm in Mice

[Figure: see text].

Mst1/2 Kinases Inhibitor, XMU-MP-1, Attenuates Angiotensin II-Induced Ascending Aortic Expansion in Hypercholesterolemic Mice

Background: Ascending and abdominal aortic aneurysms (AAs) are asymptomatic, permanent dilations of the aorta with surgical intervention as the currently available therapy. Hippo-Yap signaling cascade plays a critical role in stem cell self-renewal, tissue regeneration and organ size control. By using XMU-MP-1, a pharmacological inhibitor of the key component of Hippo-Yap signaling, MST1/2, we examined the functional contribution of Hippo-Yap in the development of AAs in Angiotensin II (AngII)-infused hypercholesterolemic mice.

Methods and Results: MST, p-MST, p-YAP, p-MOB and TAZ proteins in AngII-infused ascending and abdominal aortas were assessed by immunohistochemical and western blot analyses. To examine the effect of MST1/2 inhibition on AAs, western diet-fed low density lipoprotein (LDL) receptor −/− mice infused with AngII were administered with either vehicle or XMU-MP-1 for 5 weeks. Hippo-YAP signaling proteins were significantly elevated in AngII infused ascending and abdominal aortas. XMU-MP-1 administration resulted in the attenuation of AngII-induced ascending AAs without influencing abdominal AAs and aortic atherosclerosis. Inhibition of Hippo-YAP signaling also resulted in the suppression of AngII-induced matrix metalloproteinase 2 (MMP2) activity, macrophage accumulation, aortic medial hypertrophy and elastin breaks in the ascending aorta.

Conclusions: The present study demonstrates a pivotal role for the Hippo-YAP signaling pathway in AngII-induced ascending AA development.

Fisetin Attenuates Lipopolysaccharide-Induced Inflammatory Responses in Macrophage

Several studies have reported the efficacy and safety of polyphenols in human health; however, the verification of their efficacy remains insufficient. The aim of this study was to examine whether fisetin, one of flavonoids prevalently present in fruits and vegetables, could suppress lipopolysaccharide- (LPS-) induced inflammatory responses in macrophages. LPS increased proinflammatory mRNA abundance (MCP 1, IL-1β, and iNOS) but were suppressed by fisetin. The increment of nitric oxide by LPS, an oxidative stress factor, was attenuated by fisetin. In addition, LPS-enhanced phosphorylation of mitogen-activated protein kinase (ERK and JNK) was reduced. Finally, fisetin attenuated the expression or activity of uPA, uPAR, MMP-2, and MMP-9, which are known as associated factors of macrophage recruitment or infiltration. In conclusion, fisetin is a promising therapeutic agent for macrophage-related inflammation diseases, like sepsis and atherosclerosis.

Targeting mitochondrial fission as a potential therapeutic for abdominal aortic aneurysm

AIMS

Angiotensin II (AngII) is a potential contributor to the development of abdominal aortic aneurysm (AAA). In aortic vascular smooth muscle cells (VSMCs), exposure to AngII induces mitochondrial fission via dynamin-related protein 1 (Drp1). However, pathophysiological relevance of mitochondrial morphology in AngII-associated AAA remains unexplored. Here, we tested the hypothesis that mitochondrial fission is involved in the development of AAA.

METHODS AND RESULTS

Immunohistochemistry was performed on human AAA samples and revealed enhanced expression of Drp1. In C57BL6 mice treated with AngII plus β-aminopropionitrile, AAA tissue also showed an increase in Drp1 expression. A mitochondrial fission inhibitor, mdivi1, attenuated AAA size, associated aortic pathology, Drp1 protein induction, and mitochondrial fission but not hypertension in these mice. Moreover, western-blot analysis showed that induction of matrix metalloproteinase-2, which precedes the development of AAA, was blocked by mdivi1. Mdivi1 also reduced the development of AAA in apolipoprotein E-deficient mice infused with AngII. As with mdivi1, Drp1+/- mice treated with AngII plus β-aminopropionitrile showed a decrease in AAA compared to control Drp1+/+ mice. In abdominal aortic VSMCs, AngII induced phosphorylation of Drp1 and mitochondrial fission, the latter of which was attenuated with Drp1 silencing as well as mdivi1. AngII also induced vascular cell adhesion molecule-1 expression and enhanced leucocyte adhesion and mitochondrial oxygen consumption in smooth muscle cells, which were attenuated with mdivi1.

CONCLUSION

These data indicate that Drp1 and mitochondrial fission play salient roles in AAA development, which likely involves mitochondrial dysfunction and inflammatory activation of VSMCs.

Over-activation of NMDA receptors promotes ABCA1 degradation and foam cell formation

ATP-binding cassette transporter A1 (ABCA1) is an essential regulator of intracellular cholesterol efflux. Secreted cholesterol binds to lipid-free apolipoprotein A-I (apoA-I) in peripheral blood to constitute high-density lipoprotein cholesterol (HDL) complexes. ABCA1 protein on the surface of macrophages acts as a crucial controller in preventing cholesterol accumulation. Importantly, ABCA1 is unstable and easily degraded via a series of biochemical activities, including but not limited to calpain-mediated and ubiquitin-proteasome system-mediated processes. How accelerated ABCA1 degradation impacts disordered lipid metabolism in macrophages and foam cell formation is unclear. N-methyl d-aspartate receptors (NMDARs) are ionotropic glutamate receptors with high calcium permeability. Calcium influx via NMDARs activates downstream signaling pathways. Over-activation of NMDARs stimulated by NMDA contributes to dysfunctional lipid metabolism in macrophages and foam cell formation via promotion of calpain-mediated ABCA1 proteolysis. However, increased NMDAR activity does not affect liver X receptor expression or ABCA1 mRNA levels. Following NMDA receptor silencing or calpain inhibition, NMDA treatment did not reduce ABCA1 protein levels, nor caused lipid accumulation in macrophages. In addition, NMDAR over-activation activates NF-κB signaling to promote IL-1β and IL-6 macrophage marker expression. However, NMDAR silencing and calpain inhibition reduce inflammatory macrophage responses. In summary, our study suggests that NMDAR activation reduces surface ABCA1 protein, promotes lipid accumulation, and induces the production and secretion of many inflammatory mediators in macrophages, possibly through enhanced calpain-mediated ABCA1 protein degradation. Thus, the NMDAR receptor may be a novel pharmacologic target for atherosclerosis therapy.

Impact of Dysfunctional Protein Catabolism on Macrophage Cholesterol Handling

Protein catabolism in macrophages, which is accomplished mainly through autophagy- lysosomal degradation, ubiquitin-proteasome system, and calpains, is disturbed in atheroprone vessels. Moreover, growing evidence suggests that defects in protein catabolism interfere with cholesterol handling in macrophages. Indeed, decreases in autophagy facilitate the deposition of cholesterol in atheroprone macrophages and the subsequent development of vulnerable atherosclerotic plaques due to impaired catabolism of lipid droplets and limited efferocytic clearance of dead cells. The proteasome is responsible for the degradation of ATP-binding cassette transporters, which leads to impaired cholesterol efflux from macrophages. Overactivation of conventional calpains contributes to excessive processing of functional proteins, thereby accelerating receptor-mediated uptake of oxidized low-density lipoproteins (LDLs) and slowing cholesterol efflux. Furthermore, calpain-6, an unconventional nonproteolytic calpain in macrophages, potentiates pinocytotic uptake of native LDL and attenuates the efferocytic clearance of dead cells. Herein, we focus on recent progress in understanding how defective protein catabolism is associated with macrophage cholesterol handling and subsequent atherogenesis.

Targeting Filamin A Reduces Macrophage Activity and Atherosclerosis

BACKGROUND

The actin-binding protein FLNA (filamin A) regulates signal transduction important for cell locomotion, but the role of macrophage-specific FLNA during atherogenesis has not been explored.

METHODS

We analyzed FLNA expression in human carotid atherosclerotic plaques by immunofluorescence. We also produced mice with Flna-deficient macrophages by breeding conditional Flna-knockout mice ( Flna ^o/fl) with mice expressing Cre from the macrophage-specific lysosome M promoter ( LC). Atherosclerosis in vivo was studied by transplanting bone marrow from male Flna ^o/fl/ LC mice to atherogenic low-density lipoprotein receptor-deficient ( Ldlr^-/-) mice; and by infecting Flna ^o/fl and Flna ^o/fl/ LC mice with AdPCSK9 (adenoviral vector overexpressing proprotein convertase subtilisin/kexin type 9). Furthermore, C57BL/6 mice were infected with AdPCSK9 and then treated with the calpain inhibitor calpeptin to inhibit FLNA cleavage.

RESULTS

We found that macrophage FLNA expression was higher in advanced than in intermediate human atherosclerotic plaques. Flna ^o/fl/ LC macrophages proliferated and migrated less than controls; expressed lower levels of phosphorylated AKT and ERK1/2; exhibited reduced foam cell formation and lipid uptake; and excreted more lipids. The deficiency of Flna in macrophages markedly reduced the size of aortic atherosclerotic plaques in both Ldlr^{-/-BMT: Flnao/fl/LC} and AdPCSK9-infected Flna ^o/fl/ LC mice. Intima/media ratios and numbers of CD68-positive macrophages in atherosclerotic plaques were lower in Flna-deficient mice than in control mice. Moreover, we found that STAT3 interacts with a calpain-cleaved carboxyl-terminal fragment of FLNA. Inhibiting calpain-mediated FLNA cleavage with calpeptin in macrophages reduced nuclear levels of phosphorylated STAT3, interleukin 6 secretion, foam cell formation, and lipid uptake. Finally, calpeptin treatment reduced the size of atherosclerotic plaques in C57BL/6 mice infected with AdPCSK9.

CONCLUSIONS

Genetic inactivation of Flna and chemical inhibition of calpain-dependent cleavage of FLNA impaired macrophage signaling and function, and reduced atherosclerosis in mice, suggesting that drugs targeting FLNA may be useful in the treatment of atherosclerosis.

Exogenous Vasohibin-2 Exacerbates Angiotensin II-Induced Ascending Aortic Dilation in Mice

Background: Chronic angiotensin II (AngII) infusion promotes ascending aortic dilation in C57BL/6J mice. Meanwhile, vasohibin-2 (VASH2) is an angiogenesis promoter in neovascularization under various pathologic conditions. The aim of this study was to investigate whether exogenous VASH2 influences chronic AngII-induced ascending aortic dilation.

Methods and Results: Eight–ten-week-old male C57BL/6J mice were injected with adenovirus (Ad) expressing either VASH2 or LacZ. One week after the injection, mice were infused with either AngII or saline s.c. for 3 weeks. Mice were divided into 4 groups: AngII+VASH2, AngII+LacZ, saline+VASH2, and saline+LacZ. Overexpression of VASH2 significantly increased AngII-induced intimal areas as well as the external diameter of the ascending aorta. In addition, VASH2 overexpression promoted ascending aortic medial elastin fragmentation in AngII-infused mice, which was associated with increased matrix metalloproteinase activity and medial smooth muscle cell (SMC) apoptosis. On western blot analysis, accumulation of apoptotic signaling proteins, p21 and p53 was increased in the AngII+VASH2 group. Furthermore, transfection of human aortic SMC with Ad VASH2 increased p21 and p53 protein abundance upon AngII stimulation. Positive TUNEL staining was also detected in the same group of the human aortic SMC.

Conclusions: Exogenous VASH2 exacerbates AngII-induced ascending aortic dilation in vivo, which is associated with increased medial apoptosis and elastin fragmentation.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Calpain inhibitor I attenuates atherosclerosis and inflammation in atherosclerotic rats through eNOS/NO/NF-κB pathway

We previously reported that calpain, the Ca2+-sensitive cysteine protease, gets involved in atherogenesis. This study aimed to investigate the effects of calpain inhibitor I (CAI, 5 mg/kg per day) with or without NG-nitro-l-arginine-methyl ester (l-NAME) (100 mg/kg per day), the inhibitor of nitric oxide synthase (NOS), on atherosclerosis and inflammation in a rat model induced by high-cholesterol diet (HCD). The results demonstrated HCD increased protein expression of calpain-1 but not calpain-2 in aortic tissue. In addition, CAI reduced the thickness of atherosclerotic intima compared with HCD group, which was weakened by the l-NAME combination. CAI with or without l-NAME decreased the activity of calpain in the aorta. Also, CAI decreased the expressions of vascular cell adhesion molecule-1 (VCAM-1), intracellular cell adhesion molecule-1 (ICAM-1), and monocyte chemoattractant protein-1 (MCP-1) in the aorta at the levels of both mRNA and protein. Furthermore, CAI increased the activity and the protein expression of endothelial NOS (eNOS) accompanied by increased content of NO and downregulated the protein expression of nuclear factor κB (NF-κB) of the nucleus in the aorta. However, the abovementioned effects were at least partly cancelled by l-NAME except for the protein expression of eNOS. The results suggested that CAI attenuated atherosclerosis and inflammation through eNOS/NO/NF-κB pathway.

Defective Protein Catabolism in Atherosclerotic Vascular Inflammation

Vascular inflammation in atheroprone vessels propagates throughout the arterial tree in dyslipidemic patients, thereby accelerating atherosclerotic progression. To elucidate the mechanism of vascular inflammation, most previous studies have focused on inflammation-related signals that are sent in response to vasoactive stimuli. However, it is also important to understand how normal blood vessels become defective and start degenerating. Growing evidence suggests that major protein catabolism pathways, including the ubiquitin-proteasome, autophagy, and calpain systems, are disturbed in atheroprone vessels and contribute to the pathogenesis of atherosclerosis. Indeed, dysregulation of ubiquitin-proteasome pathways results in the accumulation of defective proteins in blood vessels, leading to vascular endothelial dysfunction and apoptosis in affected cells. Impaired autophagy-lysosomal degradation affects smooth muscle cell transformation and proliferation, as well as endothelial integrity and phagocytic clearance of cellular corpses. Dysregulation of the calpain system confers proatherogenic properties to endothelial cells, smooth muscle cells, and macrophages. In this review article, we will discuss the current information available on defective protein catabolism in atheroprone vessels and its potential interrelation with inflammation-related signals.

Calpain Inhibition Attenuates Adipose Tissue Inflammation and Fibrosis in Diet-induced Obese Mice

Adipose tissue macrophages have been proposed as a link between obesity and insulin resistance. However, the mechanisms underlying these processes are not completely defined. Calpains are calcium-dependent neutral cysteine proteases that modulate cellular function and have been implicated in various inflammatory diseases. To define whether activated calpains influence diet-induced obesity and adipose tissue macrophage accumulation, mice that were either wild type (WT) or overexpressing calpastatin (CAST Tg), the endogenous inhibitor of calpains were fed with high (60% kcal) fat diet for 16 weeks. CAST overexpression did not influence high fat diet-induced body weight and fat mass gain throughout the study. Calpain inhibition showed a transient improvement in glucose tolerance at 5 weeks of HFD whereas it lost this effect on glucose and insulin tolerance at 16 weeks HFD in obese mice. However, CAST overexpression significantly reduced adipocyte apoptosis, adipose tissue collagen and macrophage accumulation as detected by TUNEL, Picro Sirius and F4/80 immunostaining, respectively. CAST overexpression significantly attenuated obesity-induced inflammatory responses in adipose tissue. Furthermore, calpain inhibition suppressed macrophage migration to adipose tissue in vitro. The present study demonstrates a pivotal role for calpains in mediating HFD-induced adipose tissue remodeling by influencing multiple functions including apoptosis, fibrosis and inflammation.

BDA-410 Treatment Reduces Body Weight and Fat Content by Enhancing Lipolysis in Sedentary Senescent Mice

Loss of muscle mass and force with age leads to fall risk, mobility impairment, and reduced quality of life. This article shows that BDA-410, a calpain inhibitor, induced loss of body weight and fat but not lean mass or skeletal muscle proteins in a cohort of sedentary 23-month-old mice. Food and water intake and locomotor activity were not modified, whereas BDA-410 treatment decreased intramyocellular lipid and perigonadal fat, increased serum nonesterified fatty acids, and upregulated the genes mediating lipolysis and oxidation, lean phenotype, muscle contraction, muscle transcription regulation, and oxidative stress response. This finding is consistent with our recent report that lipid accumulation in skeletal myofibers is significantly correlated with slower fiber-contraction kinetics and diminished power in obese older adult mice. A proteomic analysis and immunoblot showed downregulation of the phosphatase PPP1R12B, which increases phosphorylated myosin half-life and modulates the calcium sensitivity of the contractile apparatus. This study demonstrates that BDA-410 exerts a beneficial effect on skeletal muscle contractility through new, alternative mechanisms, including enhanced lipolysis, upregulation of "lean phenotype-related genes," downregulation of the PP1R12B phosphatase, and enhanced excitation-contraction coupling. This single compound holds promise for treating age-dependent decline in muscle composition and strength.

Dysregulation of Calpain Proteolytic Systems Underlies Degenerative Vascular Disorders

Chronic vascular diseases such as atherosclerosis, aneurysms, diabetic angiopathy/retinopathy as well as fibrotic and proliferative vascular diseases are generally complicated by the progression of degenerative insults, which are characterized by endothelial dysfunction, apoptotic/necrotic cell death in vascular/immune cells, remodeling of extracellular matrix or breakdown of elastic lamella. Increasing evidence suggests that dysfunctional calpain proteolytic systems and defective calpain protein metabolism in blood vessels contribute to degenerative disorders. In vascular endothelial cells, the overactivation of conventional calpains consisting of calpain-1 and -2 isozymes can lead to the disorganization of cell-cell junctions, dysfunction of nitric oxide synthase, sensitization of Janus kinase/signal transducer and activator of transcription cascades and depletion of prostaglandin I₂, which contributes to degenerative disorders. In addition to endothelial cell dysfunctions, calpain overactivation results in inflammatory insults in macrophages and excessive fibrogenic/proliferative signaling in vascular smooth muscle cells. Moreover, calpain-6, a non-proteolytic unconventional calpain, is involved in the conversion of macrophages to a pro-atherogenic phenotype, leading to the pinocytotic deposition of low-density lipoprotein cholesterol in the cells. Here, we discuss the recent progress that has been made in our understanding of how calpain contributes to degenerative vascular disorders.

Specific calpain inhibition protects kidney against inflammaging

Calpains are ubiquitous pro-inflammatory proteases, whose activity is controlled by calpastatin, their specific inhibitor. Transgenic mice over-expressing rabbit calpastatin (CalpTG) are protected against vascular remodelling and angiotensin II-dependent inflammation. We hypothesized that specific calpain inhibition would protect against aging-related lesions in arteries and kidneys. We analysed tissues from 2-months and 2-years-old CalpTG and wild-type mice and performed high throughput RNA-Sequencing of kidney tissue in aged mice. In addition, we analysed inflammatory response in the kidney of aged CalpTG and wild-type mice, and in both in vivo (monosodium urate peritonitis) and in vitro models of inflammation. At two years, CalpTG mice had preserved kidney tissue, less vascular remodelling and less markers of senescence than wild-type mice. Nevertheless, CalpTG mice lifespan was not extended, due to the development of lethal spleen tumors. Inflammatory pathways were less expressed in aged CalpTG mice, especially cytokines related to NF-κB and NLRP3 inflammasome activation. CalpTG mice had reduced macrophage infiltration with aging and CalpTG mice produced less IL-1α and IL-1β in vivo in response to inflammasome activators. In vitro, macrophages from CalpTG mice produced less IL-1α in response to particulate activators of inflammasome. Calpains inhibition protects against inflammaging, limiting kidney and vascular lesions related to aging.

Emerging roles of calpain proteolytic systems in macrophage cholesterol handling

Calpains are Ca2+-dependent intracellular proteases that play central roles in the post-translational processing of functional proteins. In mammals, calpain proteolytic systems comprise the endogenous inhibitor calpastatin as well as 15 homologues of the catalytic subunits and two homologues of the regulatory subunits. Recent pharmacological and gene targeting studies in experimental animal models have revealed the contribution of conventional calpains, which consist of the calpain-1 and -2 isozymes, to atherosclerotic diseases. During atherogenesis, conventional calpains facilitate the CD36-dependent uptake of oxidized low-density lipoprotein (LDL), and block cholesterol efflux through ATP-binding cassette transporters in lesional macrophages, allowing the expansion of lipid-enriched atherosclerotic plaques. In addition, calpain-6, an unconventional non-proteolytic calpain, in macrophages reportedly potentiates pinocytotic uptake of native LDL, and attenuates the efferocytic clearance of apoptotic and necrotic cell corpses from the lesions. Herein, we discuss the recent progress that has been made in our understanding of how calpain contributes to atherosclerosis, in particular focusing on macrophage cholesterol handling.

Angiotensin II Peptide Vaccine Protects Ischemic Brain Through Reducing Oxidative Stress

Background and Purpose—

Medication nonadherence is one of major risk factors for the poor outcome in ischemic stroke. Vaccination is expected to solve such a problem because of its long-lasting effects, but its effect on ischemic brain damage is still unknown. Here, we focused on vaccination for renin–angiotensin system and examined the effects of angiotensin II (Ang II) peptide vaccine in permanent middle cerebral artery occlusion model in rats.

Methods—

Male Wistar rats were exposed to permanent middle cerebral artery occlusion after 3× injections of Ang II peptide vaccine, and the serum or brain level of anti–Ang II antibody was examined. The effects of the vaccine were evaluated by differences in infarction volume, brain renin–angiotensin system components, and markers for neurodegeneration and oxidative stress.

Results—

Ang II vaccination successfully produced anti–Ang II antibodies in serum without concomitant change in blood pressure. Sufficient production of serum anti–Ang II antibody led to reduction of infarct volume and induced the penetration of anti–Ang II antibody in ischemic hemisphere, with suppressed expression of Ang II type 1 receptor mRNA. Vaccinated rats with sufficient antibody production showed the reduction of Fluoro-Jade B–positive cells, spectrin fragmentation, 4-hydroxynonenal-positive cells, and Nox 2 mRNA expression.

Conclusions—

Our findings indicate that Ang II vaccination exerts neuroprotective and antioxidative effects in cerebral ischemia, with renin–angiotensin system blockade by penetration of anti–Ang II antibodies into ischemic brain lesion. Ang II peptide vaccination could be a promising approach to treat ischemic stroke.

Simvastatin inhibited oxLDL-induced proatherogenic effects through calpain-1–PPARγ–CD36 pathway

We previously reported that simvastatin, an inhibitor of HMG-CoA reductase, inhibits atherosclerosis in rats. The present study was designed to investigate the effect of simvastatin on mouse peritoneal macrophage foam cell formation, the early feature of atherosclerosis, and explore its mechanisms. The results showed that simvastatin decreased cholesterol content and DiI–oxLDL (1,1′-didodecyl 3,3,3′,3′-indocarbocyanine perchlorate – oxidized low-density lipoprotein) uptake, reduced the levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the medium, down-regulated the mRNA and protein expression of CD36 (a fatty acid receptor), and reduced the mRNA expressions of peroxisome proliferator-activated receptor gamma (PPARγ), TNF-α, and IL-6 in macrophages treated with oxLDL. However, PPARγ agonist troglitazone partly abolished the effects of simvastatin on foam cells. In addition, simvastatin reduced the protein expression of calpain-1, a Ca2+-sensitive cysteine protease, in oxLDL-treated macrophages. Furthermore, PD150606, a specific calpain inhibitor, reduced mRNA expressions of PPARγ and CD36 in macrophages treated with oxLDL. Combination of simvastatin and PD150606 had no further effect on mRNA expression of PPARγ and CD36 compared with either alone. However, over-expression of calpain-1 in macrophages partly reversed the simvastatin effects, including cell cholesterol content, mRNA expressions of PPARγ, and CD36. The results suggested that simvastatin inhibits foam cell formation of oxLDL-treated macrophages through a calpain-1–PPARγ–CD36 pathway.

Calpain research for drug discovery: challenges and potential

Calpains are a family of proteases that were scientifically recognized earlier than proteasomes and caspases, but remain enigmatic. However, they are known to participate in a multitude of physiological and pathological processes, performing 'limited proteolysis' whereby they do not destroy but rather modulate the functions of their substrates. Calpains are therefore referred to as 'modulator proteases'. Multidisciplinary research on calpains has begun to elucidate their involvement in pathophysiological mechanisms. Therapeutic strategies targeting malfunctions of calpains have been developed, driven primarily by improvements in the specificity and bioavailability of calpain inhibitors. Here, we review the calpain superfamily and calpain-related disorders, and discuss emerging calpain-targeted therapeutic strategies.

Calpain-6 confers atherogenicity to macrophages by dysregulating pre-mRNA splicing

Macrophages contribute to the development of atherosclerosis through pinocytotic deposition of native LDL-derived cholesterol in macrophages in the vascular wall. Inhibiting macrophage-mediated lipid deposition may have protective effects in atheroprone vasculature, and identifying mechanisms that potentiate this process may inform potential therapeutic interventions for atherosclerosis. Here, we report that dysregulation of exon junction complex-driven (EJC-driven) mRNA splicing confers hyperpinocytosis to macrophages during atherogenesis. Mechanistically, we determined that inflammatory cytokines induce an unconventional nonproteolytic calpain, calpain-6 (CAPN6), which associates with the essential EJC-loading factor CWC22 in the cytoplasm. This association disturbs the nuclear localization of CWC22, thereby suppressing the splicing of target genes, including those related to Rac1 signaling. CAPN6 deficiency in LDL receptor-deficient mice restored CWC22/EJC/Rac1 signaling, reduced pinocytotic deposition of native LDL in macrophages, and attenuated macrophage recruitment into the lesions, generating an atheroprotective phenotype in the aorta. In macrophages, the induction of CAPN6 in the atheroma interior limited macrophage movements, resulting in a decline in cell clearance from the lesions. Consistent with this finding, we observed that myeloid CAPN6 contributed to atherogenesis in a murine model of bone marrow transplantation. Furthermore, macrophages from advanced human atheromas exhibited increased CAPN6 induction and impaired CWC22 nuclear localization. Together, these results indicate that CAPN6 promotes atherogenicity in inflamed macrophages by disturbing CWC22/EJC systems.

Dual roles of calpain in facilitating Coxsackievirus B3 replication and prompting inflammation in acute myocarditis

Background

Viral myocarditis (VMC) treatment has long been lacking of effective methods. Our former studies indicated roles of calpain in VMC pathogenesis. This study aimed at verifying the potential of calpain in Coxsackievirus B3 (CVB3)-induced myocarditis treatment.

Methods

A transgenic mouse overexpressing the endogenous calpain inhibitor, calpastatin, was introduced in the study. VMC mouse model was established via intraperitoneal injection of CVB3 in transgenic and wild mouse respectively. Myocardial injury was assayed histologically (HE staining and pathology grading) and serologically (myocardial damage markers of CK-MB and cTnI). CVB3 replication was observed in vivo and in vitro via the capsid protein VP1 detection or virus titration. Inflammation/fibrotic factors of MPO, perforin, IFNγ, IL17, Smad3 and MMP2 were evaluated using western blot or immunohistology stain. Role of calpain in regulating fibroblast migration was studied in scratch assays.

Results

Calpastatin overexpression ameliorated myocardial injury induced by CVB3 infection significantly in transgenic mouse indicated by reduced peripheral CK-MB and cTnI levels and improved histology injury. Comparing with CVB3-infected wild type mouse, the transgenic mouse heart tissue carried lower virus load. The inflammation factors of MPO, perforin, IFNγ and IL17 were down-regulated accompanied with fibrotic agents of Smad3 and MMP2 inhibition. And calpain participated in the migration of fibroblasts in vitro, which further proves its role in regulating fibrosis.

Conclusion

Calpain plays dual roles of facilitating CVB3 replication and inflammation promotion. Calpain inhibition in CVB3-induced myocarditis showed significant treatment effect. Calpain might be a novel target for VMC treatment in clinical practices.

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Calpain is involved in virus replication in myocarditis.

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Calpain mediates inflammation infiltration in myocarditis.

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Calpain might be a candidate for viral myocarditis treatment.

Leukocyte Calpain Deficiency Reduces Angiotensin II-Induced Inflammation and Atherosclerosis But Not Abdominal Aortic Aneurysms in Mice

OBJECTIVE

Angiotensin II (AngII) infusion profoundly increases activity of calpains, calcium-dependent neutral cysteine proteases, in mice. Pharmacological inhibition of calpains attenuates AngII-induced aortic medial macrophage accumulation, atherosclerosis, and abdominal aortic aneurysm in mice. However, the precise functional contribution of leukocyte-derived calpains in AngII-induced vascular pathologies has not been determined. The purpose of this study was to determine whether calpains expressed in bone marrow (BM)-derived cells contribute to AngII-induced atherosclerosis and aortic aneurysms in hypercholesterolemic mice.

APPROACH AND RESULTS

To study whether leukocyte calpains contributed to AngII-induced aortic pathologies, irradiated male low-density lipoprotein receptor(-/-) mice were repopulated with BM-derived cells that were either wild-type or overexpressed calpastatin, the endogenous inhibitor of calpains. Mice were fed a fat-enriched diet and infused with AngII (1000 ng/kg per minute) for 4 weeks. Overexpression of calpastatin in BM-derived cells significantly attenuated AngII-induced atherosclerotic lesion formation in aortic arches, but had no effect on aneurysm formation. Using either BM-derived cells from calpain-1-deficient mice or mice with leukocyte-specific calpain-2 deficiency generated using cre-loxP recombination technology, further studies demonstrated that independent deficiency of either calpain-1 or -2 in leukocytes modestly attenuated AngII-induced atherosclerosis. Calpastatin overexpression significantly attenuated AngII-induced inflammatory responses in macrophages and spleen. Furthermore, calpain inhibition suppressed migration and adhesion of macrophages to endothelial cells in vitro. Calpain inhibition also significantly decreased hypercholesterolemia-induced atherosclerosis in the absence of AngII.

CONCLUSIONS

The present study demonstrates a pivotal role for BM-derived calpains in mediating AngII-induced atherosclerosis by influencing macrophage function.

Clonal expansion of T cells in abdominal aortic aneurysm: a role for doxycycline as drug of choice?

Most reported studies with animal models of abdominal aortic aneurysm (AAA) and several studies with patients have suggested that doxycycline favourably modifies AAA; however, a recent large long-term clinical trial found that doxycycline did not limit aneurysm growth. Thus, there is currently no convincing evidence that doxycycline reduces AAA expansion. Here, we critically review the available experimental and clinical information about the effects of doxycycline when used as a pharmacological treatment for AAA. The view that AAA can be considered an autoimmune disease and the observation that AAA tissue shows clonal expansion of T cells is placed in the light of the well-known inhibition of mitochondrial protein synthesis by doxycycline. In T cell leukaemia animal models, this inhibitory effect of the antibiotic has been shown to impede T cell proliferation, resulting in complete tumour eradication. We suggest that the available evidence of doxycycline action on AAA is erroneously ascribed to its inhibition of matrix metalloproteinases (MMPs) by competitive binding of the zinc ion co-factor. Although competitive binding may explain the inhibition of proteolytic activity, it does not explain the observed decreases of MMP mRNA levels. We propose that the observed effects of doxycycline are secondary to inhibition of mitochondrial protein synthesis. Provided that serum doxycycline levels are kept at adequate levels, the inhibition will result in a proliferation arrest, especially of clonally expanding T cells. This, in turn, leads to the decrease of proinflammatory cytokines that are normally generated by these cells. The drastic change in cell type composition may explain the changes in MMP mRNA and protein levels in the tissue samples.

Metal complexes and metalloproteases: targeting conformational diseases

In recent years many metalloproteases (MPs) have been shown to play important roles in the development of various pathological conditions. Although most of the literature is focused on matrix MPs (MMPs), many other MPs have been demonstrated to be involved in the degradation of peptides or proteins whose accumulation and dyshomeostasis are considered as being responsible for the development of conformational diseases, i.e., diseases where non-native protein conformations lead to protein aggregation. It seems clear that, at least in principle, it must be possible to control the levels of many aggregation-prone proteins not only by reducing their production, but also by enhancing their catabolism. Metal complexes that can perform this function were designed and tested according to at least two different strategies: (i) intervening on the endogenous MPs by directly or indirectly modulating their activity; (ii) acting as artificial MPs, replacing or synergistically functioning with endogenous MPs. These two different bioinorganic approaches are widely represented in the current literature and the aim of this review is to rationally organize and discuss both of them so as to give a critical insight into these approaches and highlighting their limitations and future perspectives.

Monitoring the biomolecular interactions and the activity of Zn-containing enzymes involved in conformational diseases: experimental methods for therapeutic purposes

Zinc metalloproteases (ZnMPs) participate in diverse biological reactions, encompassing the synthesis and degradation of all the major metabolites in living organisms. In particular, ZnMPs have been recognized to play a very important role in controlling the concentration level of several peptides and/or proteins whose homeostasis has to be finely regulated for the correct physiology of cells. Dyshomeostasis of aggregation-prone proteins causes pathological conditions and the development of several different diseases. For this reason, in recent years, many analytical approaches have been applied for studying the interaction between ZnMPs and their substrates/inhibitors and how environmental factors can affect enzyme activities. In this scenario, nuclear magnetic resonance, X-ray diffraction, mass spectrometric (MS), and optical methods occupy a very important role in elucidating different aspects of the ZnMPs-substrates/inhibitors interaction, ranging from identification of cleavage sites to quantitation of kinetic parameters and inhibition constants. Here, an overview of all the main achievements in the application of different experimental approaches with special attention to MS methods to the investigation of ZnMPs-substrates/inhibitors interaction is given. A general MS experimental protocol which has been proved to be useful to study such interactions is also described.

Calpain 1 inhibitor BDA-410 ameliorates α-klotho-deficiency phenotypes resembling human aging-related syndromes

Taking good care of elderly is a major challenge of our society, and thus identification of potential drug targets to reduce age-associated disease burden is desirable. α-klotho^-/- (α-kl) is a short-lived mouse model that displays multiple phenotypes resembling human aging-related syndromes. Such ageing phenotype of α-kl^-/- mice is associated with activation of a proteolytic enzyme, Calpain-1. We hypothesized that uncontrolled activation of calpain-1 might be causing age-related phenotypes in α-kl-deficient mice. We found that daily administration of BDA-410, a calpain-1 inhibitor, strikingly ameliorated multiple aging-related phenotypes. Treated mice showed recovery of reproductive ability, increased body weight, reduced organ atrophy, and suppression of ectopic calcifications, bone mineral density reduction, pulmonary emphysema and senile atrophy of skin. We also observed ectopic expression of FGF23 in calcified arteries of α-kl^-/- mice, which might account for the clinically observed association of increased FGF23 level with increased risk of cardiovascular mortality. These findings allow us to propose that modulation of calpain-1 activity is a potential therapeutic option for delaying age-associated organ pathology, particularly caused by the dysregulation of mineral ion homeostasis.

Calpastatin prevents NF-κB-mediated hyperactivation of macrophages and attenuates colitis

Calpain enzymes proteolytically modulate cellular function and have been implicated in inflammatory diseases. In this study, we found that calpain levels did not differ between intestinal tissues from inflammatory bowel disease (IBD) patients and healthy controls, but IBD tissues showed increased levels of the endogenous calpain inhibitor, calpastatin (CAST). To investigate the role of CAST in the immune system during IBD, mice were x-ray irradiated, reconstituted with either CAST-knockout (KO) or wild-type (WT) bone marrow, and subjected to dextran sulfate sodium-induced colitis. CAST-KO recipients with induced colitis exhibited more severe weight loss, bloody diarrhea, and anemia compared with WT controls. Histological evaluation of colons from KO recipients with colitis revealed increased inflammatory pathology. Macrophages purified from the colons of KO recipients had higher IL-6, TNF-α, and IFN-γ mRNA levels compared with WT controls. Mechanistic investigations using small interfering RNA and KO bone marrow to generate CAST-deficient macrophages showed that CAST deficiency during activation with bacterial pathogen associated molecular patterns, including heat-killed Enterococcus faecalis or CpG DNA, led to increased IκB cleavage, NF-κB nuclear localization, and IL-6 and TNF-α secretion. Thus, CAST plays a central role in regulating macrophage activation and limiting pathology during inflammatory disorders like IBD.

Calpain-2 compensation promotes angiotensin II-induced ascending and abdominal aortic aneurysms in calpain-1 deficient mice

Background and Objective

Recently, we demonstrated that angiotensin II (AngII)-infusion profoundly increased both aortic protein and activity of calpains, calcium-activated cysteine proteases, in mice. In addition, pharmacological inhibition of calpain attenuated AngII-induced abdominal aortic aneurysm (AA) in mice. Recent studies have shown that AngII infusion into mice leads to aneurysmal formation localized to the ascending aorta. However, the precise functional contribution of calpain isoforms (-1 or -2) in AngII-induced abdominal AA formation is not known. Similarly, a functional role of calpain in AngII-induced ascending AA remains to be defined. Using BDA-410, an inhibitor of calpains, and calpain-1 genetic deficient mice, we examined the relative contribution of calpain isoforms in AngII-induced ascending and abdominal AA development.

Methodology/Results

To investigate the relative contribution of calpain-1 and -2 in development of AngII-induced AAs, male LDLr −/− mice that were either calpain-1 +/+ or −/− were fed a saturated fat-enriched diet and infused with AngII (1,000 ng/kg/min) for 4 weeks. Calpain-1 deficiency had no significant effect on body weight or blood pressure during AngII infusion. Moreover, calpain-1 deficiency showed no discernible effects on AngII-induced ascending and abdominal AAs. Interestingly, AngII infusion induced increased expression of calpain-2 protein, thus compensating for total calpain activity in aortas of calpain-1 deficient mice. Oral administration of BDA-410, a calpain inhibitor, along with AngII-infusion significantly attenuated AngII-induced ascending and abdominal AA formation in both calpain-1 +/+ and −/− mice as compared to vehicle administered mice. Furthermore, BDA-410 administration attenuated AngII-induced aortic medial hypertrophy and macrophage accumulation. Western blot and immunostaining analyses revealed BDA-410 administration attenuated AngII-induced C-terminal fragmentation of filamin A, an actin binding cytoskeletal protein in aorta.

Conclusion

Calpain-2 compensates for loss of calpain-1, and both calpain isoforms are involved in AngII-induced aortic aneurysm formation in mice.

Novel mechanisms of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a common but asymptomatic disease that has high susceptibility to rupture. Current therapeutic options are limited to surgical procedures because no pharmacological approaches have been proven to decrease either expansion or rupture of human AAAs. The current dearth of effective medical treatment is attributed to insufficient understanding of the mechanisms underlying the initiation, propagation and rupture of AAAs. This review will emphasize recent advances in mechanistic studies that may provide insights into potential pharmacological treatments for this disease. While we primarily focus on recent salient findings, we also discuss mechanisms that continue to be controversial depending on models under study. Despite the progress on exploring mechanisms of experimental AAAs, ultimate validation of mechanisms will require completion of prospective double-blinded clinical trials. In addition, we advocate increased emphasis of collaborative studies using animal models and human tissues for determination of mechanisms that explore expansion and rupture of existing AAAs.

Calpain and atherosclerosis

This review highlights the pro-atherogenic roles of Ca(2+)-sensitive intracellular protease calpains. Among more than ten species of calpain isozymes, µ- and m-calpains have been characterized most extensively. These two isozymes are ubiquitously expressed in mammalian tissues, including blood vessels, and tightly regulate functional molecules in the vascular component cells through limited proteolytic cleavage. Indeed, previous cell-based experiments showed that calpains play significant roles in nitric oxide production in vascular endothelial cells (ECs), maintenance of EC barrier function and angiogenesis for maintaining vascular homeostasis. Recently, we demonstrated that modified-low density lipoprotein (LDL)-induced m-calpain causes hyperpermeability in ECs, leading to the infiltration of monocytes/macrophages and plasma lipids into the intimal spaces (Miyazaki T. et al., Circulation. 2011; 124: 2522-2532). Calpains also mediate oxidized LDL-induced apoptotic death in ECs. In monocytes/macrophages, calpains induce proteolytic degradation of ATP-binding cassette transporter A1 (ABCA1) and G1 (ABCG1), which results in impaired cholesterol efflux and subsequent macrophage foam cell formation. In vascular smooth muscle cells, calpains may be involved in the conversion from contractile phenotype to proliferative phenotype. In hepatocytes, calpains disrupt the biogenesis of high-density lipoprotein via proteolytic degradation of ABCA1. Thus, calpains may serve as novel candidate molecular targets for control of atherosclerosis.

Involvement of the renin-angiotensin system in abdominal and thoracic aortic aneurysms

Aortic aneurysms are relatively common maladies that may lead to the devastating consequence of aortic rupture. AAAs (abdominal aortic aneurysms) and TAAs (thoracic aortic aneurysms) are two common forms of aneurysmal diseases in humans that appear to have distinct pathologies and mechanisms. Despite this divergence, there are numerous and consistent demonstrations that overactivation of the RAS (renin-angiotensin system) promotes both AAAs and TAAs in animal models. For example, in mice, both AAAs and TAAs are formed during infusion of AngII (angiotensin II), the major bioactive peptide in the RAS. There are many proposed mechanisms by which the RAS initiates and perpetuates aortic aneurysms, including effects of AngII on a diverse array of cell types and mediators. These experimental findings are complemented in humans by genetic association studies and retrospective analyses of clinical data that generally support a role of the RAS in both AAAs and TAAs. Given the lack of a validated pharmacological therapy for any form of aortic aneurysm, there is a pressing need to determine whether the consistent findings on the role of the RAS in animal models are translatable to humans afflicted with these diseases. The present review compiles the recent literature that has shown the RAS as a critical component in the pathogenesis of aortic aneurysms.

Calpain inhibition stabilizes the platelet proteome and reactivity in diabetes

Platelets from patients with diabetes are hyperreactive and demonstrate increased adhesiveness, aggregation, degranulation, and thrombus formation, processes that contribute to the accelerated development of vascular disease. Part of the problem seems to be dysregulated platelet Ca2+ signaling and the activation of calpains, which are Ca2+-activated proteases that result in the limited proteolysis of substrate proteins and subsequent alterations in signaling. In the present study, we report that the activation of μ- and m-calpain in patients with type 2 diabetes has profound effects on the platelet proteome and have identified septin-5 and the integrin-linked kinase (ILK) as novel calpain substrates. The calpain-dependent cleavage of septin-5 disturbed its association with syntaxin-4 and promoted the secretion of α-granule contents, including TGF-β and CCL5. Calpain was also released by platelets and cleaved CCL5 to generate a variant with enhanced activity. Calpain activation also disrupted the ILK-PINCH-Parvin complex and altered platelet adhesion and spreading. In diabetic mice, calpain inhibition reversed the effects of diabetes on platelet protein cleavage, decreased circulating CCL5 levels, reduced platelet-leukocyte aggregate formation, and improved platelet function. The results of the present study indicate that diabetes-induced platelet dysfunction is mediated largely by calpain activation and suggest that calpain inhibition may be an effective way of preserving platelet function and eventually decelerating atherothrombosis development.

Regulation and physiological roles of the calpain system in muscular disorders

Calpains, a family of Ca(2+)-dependent cytosolic cysteine proteases, can modulate their substrates' structure and function through limited proteolytic activity. In the human genome, there are 15 calpain genes. The most-studied calpains, referred to as conventional calpains, are ubiquitous. While genetic studies in mice have improved our understanding about the conventional calpains' physiological functions, especially those essential for mammalian life as in embryogenesis, many reports have pointed to overactivated conventional calpains as an exacerbating factor in pathophysiological conditions such as cardiovascular diseases and muscular dystrophies. For treatment of these diseases, calpain inhibitors have always been considered as drug targets. Recent studies have introduced another aspect of calpains that calpain activity is required to protect the heart and skeletal muscle against stress. This review summarizes the functions and regulation of calpains, focusing on the relevance of calpains to cardiovascular disease.