Calpain 10 is required for cell viability and is decreased in the aging kidney

Role of renal tubular programed cell death in diabetic kidney disease

The pathogenic mechanism of diabetic kidney disease (DKD) is involved in various functions; however, its inadequate characterisation limits the availability of effective treatments. Tubular damage is closely correlated with renal function and is thought to be the main contributor to the injury observed in early DKD. Programed cell death (PCD) occurs during the biological development of the living body. Accumulating evidence has clarified the fundamental role of abnormalities in tubular PCD during DKD pathogenesis. Among PCD types, classical apoptosis, autophagic cell death, and pyroptosis are the most studied and will be the focus of this review. Our review aims to elucidate the current knowledge of the mechanism of DKD and the potential therapeutic potential of drugs targeting tubular PCD pathways in DKD.

In Vivo Monitoring of Calpain Activity by Forster Resonance Energy Transfer

Calpains are a 15-member class of calcium-activated nonlysosomal neutral proteases. They are involved in many cellular processes and are highly upregulated in pathological conditions. Some are ubiquitously expressed (CAPN1, CAPN2, CAPN4, CAPN5, CAPN7, and CAPN10), but others are thought to be localized in specific tissues. The monitoring of in vivo calpain activity is required for physiological, pathological, and therapeutic evaluations. This past decade, a tool for monitoring calpain activity in such conditions was developed using Forster resonance energy transfer (FRET). Studies showed that the level of calpain activity correlates with a decrease in FRET between the two fluorescent proteins. This chapter describes the methodologies from the design of the construct to the imaging procedure and analysis to evaluate ubiquitous calpain activity in vivo.

Role of Calpain in Pathogenesis of Human Disease Processes

Calpains are a 15-member class of calcium activated nonlysosomal neutral proteases which are involved in a broad range of cellular function. Calpains are usually localized to the cytosol and within mitochondria. Calpastatin is an endogenous protein that specifically binds to and inhibits calpain. Overactivation of calpain has been implicated in a number of disease processes of the brain, eyes, heart, lungs, pancreas, kidneys, vascular system and skeletal muscle. Therefore, calpain may serve as a potential therapeutic target for a wide variety of disease processes. This review briefly outlines the current literature regarding the involvement of calpain overactivation in the pathogenesis of almost every organ in the body.

Role of the calpain on the development of diabetes mellitus and its chronic complications

Diabetes mellitus (DM) is associated with acute and chronic complications that cause major morbidity and significant mortality. Calpains, a family of Ca(2+)-dependent cytosolic cysteine proteases, can modulate their substrates' structure and function through limited proteolytic activity. Calpain is a ubiquitous calcium-sensitive protease that is essential for normal physiologic function. However, alterations in calcium homeostasis lead to pathologic activation of calpain in diabetes mellitus. Since not much is known on the relationship between calpain and diabetes mellitus, this review outlines the contribution of calpain to chronic complications of diabetes mellitus, such as diabetic cardiomyopathy, diabetic nephropathy and diabetic retinopathy.

Mitochondrial m-calpain opens the mitochondrial permeability transition pore in ischemia-reperfusion

BACKGROUND/OBJECTIVES

Opening of the mitochondrial permeability transition pore (mPTP) is involved in ischemia-reperfusion injury. Isoforms of Ca(2+)-activated cysteine proteases, calpains, are implicated in the development of myocardial infarction in ischemia-reperfusion. Growing evidence has revealed the presence of calpains in the mitochondria. We aimed to characterize mitochondrial calpains in the rat heart and to investigate the roles of calpains in mPTP opening after ischemia-reperfusion.

METHODS AND RESULTS

Western blotting analysis showed the expression of μ-calpain, m-calpain and calpain 10 in mitochondria isolated from male Sprague-Dawley rats, but casein zymography detected only m-calpain activity. Subcellular fractionation of mitochondria demonstrated the distribution of m-calpain to the matrix fraction. Addition of >500μM of Ca(2+) to isolated mitochondria induced mitochondrial swelling, reflecting mPTP opening, and calpain activation. Ca(2+)-induced mitochondrial swelling was inhibited partially by the calpain inhibitor calpeptin. These results support a partial contribution of calpain in the opening of the mPTP. The addition of Ca(2+) to the mitochondria induced inactivation of complex I of the electron transport chain, and cleavage of the ND6 complex I subunit, which were inhibited by calpeptin. Mitochondria isolated from rat hearts that underwent 30min of coronary occlusion followed by 30min of reperfusion showed activation of mitochondrial calpains, ND6 cleavage, complex I inactivation, and mPTP opening, which were inhibited by pretreatment with calpain inhibitor 1.

CONCLUSIONS

We demonstrated for the first time the presence of mitochondrial matrix m-calpain, and its contribution to complex I inactivation and mPTP opening after postischemic reperfusion in the rat heart.

Calpain-10 Activity Underlies Angiotensin II-Induced Aldosterone Production in an Adrenal Glomerulosa Cell Model

Aldosterone is a steroid hormone important in the regulation of blood pressure. Aberrant production of aldosterone results in the development and progression of diseases including hypertension and congestive heart failure; therefore, a complete understanding of aldosterone production is important for developing more effective treatments. Angiotensin II (AngII) regulates steroidogenesis, in part through its ability to increase intracellular calcium levels. Calcium can activate calpains, proteases classified as typical or atypical based on the presence or absence of penta-EF-hands, which are involved in various cellular responses. We hypothesized that calpain, in particular calpain-10, is activated by AngII in adrenal glomerulosa cells and underlies aldosterone production. Our studies showed that pan-calpain inhibitors reduced AngII-induced aldosterone production in 2 adrenal glomerulosa cell models, primary bovine zona glomerulosa and human adrenocortical carcinoma (HAC15) cells, as well as CYP11B2 expression in the HAC15 cells. Although AngII induced calpain activation in these cells, typical calpain inhibitors had no effect on AngII-elicited aldosterone production, suggesting a lack of involvement of classical calpains in this process. However, an inhibitor of the atypical calpain, calpain-10, decreased AngII-induced aldosterone production. Consistent with this result, small interfering RNA (siRNA)-mediated knockdown of calpain-10 inhibited aldosterone production and CYP11B2 expression, whereas adenovirus-mediated overexpression of calpain-10 resulted in increased AngII-induced aldosterone production. Our results indicate that AngII-induced activation of calpain-10 in glomerulosa cells underlies aldosterone production and identify calpain-10 or its downstream pathways as potential targets for the development of drug therapies for the treatment of hypertension.

The calpain system and diabetes

Diabetes mellitus is recognized as a clinical syndrome that is characterized by hyperglycemia due to deficiency of insulin. The global prevalence of diabetes has been estimated to increase from 4% (1995) to 5.4% by the year 2025. Insulin dependent diabetes mellitus (IDDM/Type-1) in human, generating hyperglycemia due to insulin deficiency as a consequence of destructing beta cells in the pancreatic islets. Non-insulin dependent diabetes mellitus (NIDDM/Type-II), is a multifactorial, exact biochemical and genetic defect which has not yet been elucidated completely. Calpains seem to play a role in NIDDM and IDDM. Positional cloning experiments revealed that there is a NIDDM susceptibility to calpain 10 (CAPN10). Increased calpain activity and leukocyte trafficking were noticed in the microcirculation in ZDF (Zuker diabetic fatty) rats. Exercise and low body weight play a significant role in reducing calpains expression or elevating the calpains degradation in the skeletal muscle of NIDDM rats. Numerous investigations have been reported that non-coding polymorphisms in CAPN10 proteins might be involved in the NIDDM. Calpain and its mRNA presence had been reported in tissues from many mammalian species. CAPN10 and other calpains seem to be linked to glucose metabolism, insulin secretion and action pathways. This review will give an overview of the role of calpain in NIDDM and IDDM.

Role of calpain-10 in the development of diabetes mellitus and its complications

Calpain activity has been implicated in several cellular processes such as cell signaling, apoptosis, exocytosis, mitochondrial metabolism and cytoskeletal remodeling. Evidence has indicated that the impairment of calpain expression and the activity of different calpain family members are involved in diverse pathologies. Calpain-10 has been implicated in the development of type 2 diabetes, and polymorphisms in the CAPN10 gene have been associated with an increased risk of developing this disease. The present work focused on the molecular biology of calpain-10, supporting its key participation in glucose metabolism. Current knowledge regarding the role of calpain-10 in the development of type 2 diabetes mellitus and diabetes-related diseases is additionally reviewed.

Calpain 10 homology modeling with CYGAK and increased lipophilicity leads to greater potency and efficacy in cells

Calpain 10 is a ubiquitously expressed mitochondrial and cytosolic Ca(2+)-regulated cysteine protease in which overexpression or knockdown leads to mitochondrial dysfunction and cell death. We previously identified a potent and specific calpain 10 peptide inhibitor (CYGAK), but it was not efficacious in cells. Therefore, we created a homology model using the calpain 10 amino acid sequence and calpain 1 3-D structure and docked CYGAK in the active site. Using this model we modified the inhibitor to improve potency 2-fold (CYGAbuK). To increase cellular efficacy, we created CYGAK-S-phenyl-oleic acid heterodimers. Using renal mitochondrial matrix CYGAK, CYGAK-OC, and CYGAK-ON had IC(50)'s of 70, 90, and 875 nM, respectively. Using isolated whole renal mitochondria CYGAK, CYGAK-OC, and CYGAK-ON had IC(50)'s of 95, 196, and >10,000 nM, respectively. Using renal proximal tubular cells (RPTC) in primary culture, 30 min exposures to CYGAK-OC and CYGAbuK-OC decreased cellular calpain activity approximately 20% at 1 μM, and concentrations up to 100 μM had no additional effect. RPTC treated with 10 μM CYGAK-OC for 24 h induced accumulation of ATP synthase β and NDUFB8, two calpain 10 substrates. In summary, we used molecular modeling to improve the potency of CYGAK, while creating CYGAK-oleic acid heterodimers to improve efficacy in cells. Since calpain 10 has been implicated in type 2 diabetes and renal aging, the use of this inhibitor may contribute to elucidating the role of calpain 10 in these and other diseases.

Loss of calpain 10 causes mitochondrial dysfunction during chronic hyperglycemia

We showed that renal calpain 10, a mitochondrial and cytosolic Ca(2+)-regulated cysteine protease, is specifically decreased in kidneys of diabetic rats and mice, and is associated with diabetic nephropathy. The goals of this study were to examine renal calpain 10 and mitochondrial dysfunction in streptozotocin-induced hyperglycemic rats and determine the effects of siRNA-mediated knock down of renal calpain 10 on mitochondrial function. Four weeks after streptozotocin injection, calpain 10 protein and mRNA were decreased and calpain 10 substrates accumulated. We detected increased state 2 respiration in isolated renal mitochondria and increased markers of mitochondrial fission and mitophagy. All changes were prevented by daily insulin injection. Compared to scrambled siRNA, calpain 10 siRNA resulted in a marked decrease in renal calpain 10 at 2, 5 and 7 days. In concert with the loss of renal calpain 10, calpain 10 substrates accumulated, mitochondrial fusion decreased, mitochondrial fission and mitophagy increased. In summary, insulin-sensitive hyperglycemia induced loss of renal calpain 10 is correlated with renal mitochondrial dysfunction, fission and mitophagy, and specific depletion of renal calpain 10 produces similar mitochondrial defects. These results provide evidence that diabetes-induced renal mitochondrial dysfunction and renal injury may directly result from the loss of renal calpain 10.

Calpains, mitochondria, and apoptosis

Mitochondrial activity is critical for efficient function of the cardiovascular system. In response to cardiovascular injury, mitochondrial dysfunction occurs and can lead to apoptosis and necrosis. Calpains are a 15-member family of Ca(2+)-activated cysteine proteases localized to the cytosol and mitochondria, and several have been shown to regulate apoptosis and necrosis. For example, in endothelial cells, Ca(2+) overload causes mitochondrial calpain 1 cleavage of the Na(+)/Ca(2+) exchanger leading to mitochondrial Ca(2+) accumulation. Also, activated calpain 1 cleaves Bid, inducing cytochrome c release and apoptosis. In renal cells, calpains 1 and 2 promote apoptosis and necrosis by cleaving cytoskeletal proteins, which increases plasma membrane permeability and cleavage of caspases. Calpain 10 cleaves electron transport chain proteins, causing decreased mitochondrial respiration and excessive activation, or inhibition of calpain 10 activity induces mitochondrial dysfunction and apoptosis. In cardiomyocytes, calpain 1 activates caspase 3 and poly-ADP ribose polymerase during tumour necrosis factor-α-induced apoptosis, and calpain 1 cleaves apoptosis-inducing factor after Ca(2+) overload. Many of these observations have been elucidated with calpain inhibitors, but most calpain inhibitors are not specific for calpains or a specific calpain family member, creating more questions. The following review will discuss how calpains affect mitochondrial function and apoptosis within the cardiovascular system.

Mitochondrial calpain 10 is degraded by Lon protease after oxidant injury

Calpain 10 is ubiquitously expressed and is one of four mitochondrial matrix proteases. We determined that over-expression or knock-down of mitochondrial calpain 10 results in cell death, demonstrating that mitochondrial calpain 10 is required for viability. Thus, we studied calpain 10 degradation in isolated mitochondrial matrix, mitochondria and in renal proximal tubular cells (RPTC) under control and toxic conditions. Using isolated renal cortical mitochondria and mitochondrial matrix, calpain 10 underwent rapid degradation at 37°C that was blocked with Lon inhibitors but not by calpain or proteasome inhibitors. While exogenous Ca(2+) addition, Ca(2+) chelation or exogenous ATP addition had no effect on calpain 10 degradation, the oxidants tert-butyl hydroperoxide (TBHP) or H(2)O(2) increased the rate of degradation. Using RPTC, mitochondrial and cytosolic calpain 10 increased in the presence of MG132 (Lon/proteasome inhibitor) but only cytosolic calpain 10 increased in the presence of epoxomicin (proteasome inhibitor). Furthermore, TBHP and H(2)O(2) oxidized mitochondrial calpain 10, decreased mitochondrial, but not cytosolic calpain 10, and pretreatment with MG132 blocked TBHP-induced degradation of calpain 10. In summary, mitochondrial calpain 10 is selectively degraded by Lon protease under basal conditions and is enhanced under and oxidizing conditions, while cytosolic calpain 10 is degraded by the proteasome.

Chronic high glucose downregulates mitochondrial calpain 10 and contributes to renal cell death and diabetes-induced renal injury

Whereas most calpains are cytosolic proteases, calpain 10 is resident in mitochondria and is important in mitochondrial homeostasis. Because calpain 10 has been implicated in type 2 diabetes, we studied its possible role in diabetes-induced renal dysfunction. We treated renal proximal tubular cells with high glucose (17 mmol/l) and found decreased mitochondrial calpain 10 mRNA and protein at 96 h compared with cells incubated with 0 or 5 mmol/l glucose or 17 mmol/l D-mannitol. High glucose increased mitochondrial calpain 10 substrates (NDUFB8 and ATP synthase β), decreased basal and uncoupled respiration, and initiated cell apoptosis as indicated by cleaved caspase 3 and nuclear condensation. Renal calpain 10 protein and mRNA were specifically decreased in streptozotocin-induced diabetic rats with kidney dysfunction, and in diabetic ob/ob mice. In agreement with our in vitro data, the kidneys of streptozotocin-induced diabetic rats had elevated calpain 10 substrates and cleaved caspase 3. Finally, specific siRNA-induced knockdown of calpain 10 in the proximal tubules of control rats resulted in decreased renal function as evidenced by increased serum creatinine, and increased caspase 3 cleavage compared with rats receiving scrambled siRNA. Thus, the glucose-induced loss of calpain 10 in vivo results in renal cell apoptosis and organ failure through accumulation of mitochondrial calpain 10 substrates and mitochondrial dysfunction. Whether this is a major cause of the decreased renal function in diabetic nephropathy will require further studies.

Accumulation of long-chain glycosphingolipids during aging is prevented by caloric restriction

Background

Chronic kidney disease and end-stage renal disease are major causes of morbidity and mortality that are seen far more commonly in the aged population. Interestingly, kidney function declines during aging even in the absence of underlying renal disease. Declining renal function has been associated with age-related cellular damage and dysfunction with reports of increased levels of apoptosis, necrosis, and inflammation in the aged kidney. Bioactive sphingolipids have been shown to regulate these same cellular processes, and have also been suggested to play a role in aging and cellular senescence.

Methodology/Principal Findings

We hypothesized that alterations in kidney sphingolipids play a role in the declining kidney function that occurs during aging. To begin to address this, the sphingolipid profile was measured in young (3 mo), middle aged (9 mo) and old (17 mo) C57BL/6 male mice. Interestingly, while modest changes in ceramides and sphingoid bases were evident in kidneys from older mice, the most dramatic elevations were seen in long-chain hexosylceramides (HexCer) and lactosylceramides (LacCer), with C14- and C16-lactosylceramides elevated as much as 8 and 12-fold, respectively. Increases in long-chain LacCers during aging are not exclusive to the kidney, as they also occur in the liver and brain. Importantly, caloric restriction, previously shown to prevent the declining kidney function seen in aging, inhibits accumulation of long-chain HexCer/LacCers and prevents the age-associated elevation of enzymes involved in their synthesis. Additionally, long-chain LacCers are also significantly elevated in human fibroblasts isolated from elderly individuals.

Conclusion/Significance

This study demonstrates accumulation of the glycosphingolipids HexCer and LacCer in several different organs in rodents and humans during aging. In addition, data demonstrate that HexCer and LacCer metabolism is regulated by caloric restriction. Taken together, data suggest that HexCer/LacCers are important mediators of cellular processes fundamental to mammalian aging.

Aging increases oxidative stress and renal expression of oxidant and antioxidant enzymes that are associated with an increased trend in systolic blood pressure

The aim of this study was to investigate whether the effects of aging on oxidative stress markers and expression of major oxidant and antioxidant enzymes associate with impairment of renal function and increases in blood pressure. To explore this, we determined age-associated changes in lipid peroxidation (urinary malondialdehyde), plasma and urinary hydrogen peroxide (H₂O₂) levels, as well as renal H₂O₂ production, and the expression of oxidant and antioxidant enzymes in young (13 weeks) and old (52 weeks) male Wistar Kyoto (WKY) rats. Urinary lipid peroxidation levels and H₂O₂ production by the renal cortex and medulla of old rats were higher than their young counterparts. This was accompanied by overexpression of NADPH oxidase components Nox4 and p22^phox in the renal cortex of old rats. Similarly, expression of superoxide dismutase (SOD) isoforms 2 and 3 and catalase were increased in the renal cortex from old rats. Renal function parameters (creatinine clearance and fractional excretion of sodium), diastolic blood pressure and heart rate were not affected by aging, although slight increases in systolic blood pressure were observed during this 52-week period. It is concluded that overexpression of renal Nox4 and p22^phox and the increases in renal H₂O₂ levels in aged WKY does not associate with renal functional impairment or marked increases in blood pressure. It is hypothesized that lack of oxidative stress-associated effects in aged WKY rats may result from increases in antioxidant defenses that counteract the damaging effects of H₂O₂.

Protein aggregation as a paradigm of aging

The process of physiological decline leading to death of the individual is driven by the deteriorating capacity to withstand extrinsic and intrinsic hazards, resulting in damage accumulation with age. The dynamic changes with time of the network governing the outcome of misfolded proteins, exemplifying as intrinsic hazards, is considered here as a paradigm of aging. The main features of the network, namely, the non-linear increase of damage and the presence of amplifying feedback loops within the system are presented through a survey of the different components of the network and related cellular processes in aging and disease.

Ageing mouse kidney--not always the SAME old story

BACKGROUND

As interest in the ageing kidney grows rapidly, more experimental ageing studies are conducted in the field. One of the main obstacles that researchers have to face is that studies in old animals are often less reproducible than in young animals. We have observed that the aged animal's provenance can be an overlooked factor accounting for such experimental heterogeneity.

METHODS

Male C57BL/6J mice aged 19-22 months were purchased from four different suppliers. Baseline renal parameters were evaluated by measuring serum urea, serum creatinine and proteinuria. Renal morphology was analysed by quantifying glomerulosclerosis, interstitial fibrosis and amyloid deposits on paraffin sections stained with PAS, Masson trichrome, Sirius red and Congo red.

RESULTS

We found normal renal ageing in mice from three sources, but an unexpected renal pathology in mice from one major European supplier. Mice from this supplier had significantly elevated serum urea, creatinine values and an increased urinary protein excretion. Corresponding kidneys displayed massive glomerulosclerosis with evidence of amyloid deposits and increased interstitial fibrosis.

CONCLUSIONS

Supplier-dependent differences, such as observed here, can explain irreproducibility of experimental results in renal ageing research. This can be avoided by careful baseline analysis prior to in vivo experiments.