Attenuated mesangial cell proliferation related to store-operated Ca2+ entry in aged rat: the role of STIM 1 and Orai 1

LncRNA MEG3 inhibits renal fibrinoid necrosis of diabetic nephropathy via the MEG3/miR-21/ORAI1 axis

INTRODUCTION

Diabetic nephropathy (DN) is one of the most common and lethal diabetic complications worldwide and is associated with a high risk of mortality. However, the exact mechanism behind its development is unknown. The mesangial cells (MCs) and non-coding RNAs are critical for DN, but it is unknown whether a MEG3/miR-21/ORAI1 regulatory axis exists in MCs. Hence, in this study, we aimed to understand whether the MEG3/miR-21/ORAI1 regulatory axis has a role in the pathophysiology of DN.

RESULTS

We demonstrated that high-glucose stimuli downregulated MEG3 and ORAI1 expression while enhancing miR-21 expression. Exogenous miR-21 mimics inhibited ORAI1 expression, which was partially salvaged or reversed by MEG3 overexpression. Furthermore, RIP assay demonstrated that the beads labeled with AGO2 antibody could enrich more miR-21 and MEG3 than those labeled with control IgG antibody; both of them formed the RNA-induced silencing complex. Further, the biochemical indicators of db/db mice significantly improved, and renal fibrinoid necrosis was ameliorated using a miR-21 inhibitor.

CONCLUSION

The MEG3/miR-21/ORAI1 axis regulates the manifestation of DN in diabetic mice and MCs, and the miR-21 inhibitor can be a potential therapeutic strategy to alleviate DN, once the presence of such an axis is found in humans.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Orai-vascular endothelial-cadherin signaling complex regulates high-glucose exposure-induced increased permeability of mouse aortic endothelial cells

INTRODUCTION

Diabetes-associated endothelial barrier function impairment might be linked to disturbances in Ca²⁺ homeostasis. To study the role and molecular mechanism of Orais-vascular endothelial (VE)-cadherin signaling complex and its downstream signaling pathway in diabetic endothelial injury using mouse aortic endothelial cells (MAECs).

RESEARCH DESIGN AND METHODS

The activity of store-operated Ca²⁺ entry (SOCE) was detected by calcium imaging after 7 days of high-glucose (HG) or normal-glucose (NG) exposure, the expression levels of Orais after HG treatment was detected by western blot analysis. The effect of HG exposure on the expression of phosphorylated (p)-VE-cadherin and VE-cadherin on cell membrane was observed by immunofluorescence assay. HG-induced transendothelial electrical resistance was examined in vitro after MAECs were cultured in HG medium. FD-20 permeability was tested in monolayer aortic endothelial cells through transwell permeability assay. The interactions between Orais and VE-cadherin were detected by co-immunoprecipitation and immunofluorescence technologies. Immunohistochemical experiment was used to detect the expression changes of Orais, VE-cadherin and p-VE-cadherin in aortic endothelium of mice with diabetes.

RESULTS

(1) The expression levels of Orais and activity of SOCE were significantly increased in MAECs cultured in HG for 7 days. (2) In MAECs cultured in HG for 7 days, the ratio of p-VE-cadherin to VE-cadherin expressed on the cell membrane and the FD-20 permeability in monolayer endothelial cells increased, indicating that intercellular permeability increased. (3) Orais and VE-cadherin can interact and enhance the interaction ratio through HG stimulation. (4) In MAECs cultured with HG, the SOCE activator ATP enhanced the expression level of p-VE-cadherin, and the SOCE inhibitor BTP2 decreased the expression level of p-VE-cadherin. (5) Significantly increased expression of p-VE-cadherin and Orais in the aortic endothelium of mice with diabetes.

CONCLUSION

HG exposure stimulated increased expression of Orais in endothelial cells, and increased VE-cadherin phosphorylation through Orais-VE-cadherin complex and a series of downstream signaling pathways, resulting in disruption of endothelial cell junctions and initiation of atherosclerosis.

Store-operated calcium entry: Pivotal roles in renal physiology and pathophysiology

Research conducted over the last two decades has dramatically advanced the understanding of store-operated calcium channels (SOCC) and their impact on renal function. Kidneys contain many types of cells, including those specialized for glomerular filtration (fenestrated capillary endothelium, podocytes), water and solute transport (tubular epithelium), and regulation of glomerular filtration and renal blood flow (vascular smooth muscle cells, mesangial cells). The highly integrated function of these myriad cells effects renal control of blood pressure, extracellular fluid volume and osmolality, electrolyte balance, and acid-base homeostasis. Many of these cells are regulated by Ca²⁺ signaling. Recent evidence demonstrates that SOCCs are major Ca²⁺ entry portals in several renal cell types. SOCC is activated by depletion of Ca²⁺ stores in the sarco/endoplasmic reticulum, which communicates with plasma membrane SOCC via the Ca²⁺ sensor Stromal Interaction Molecule 1 (STIM1). Orai1 is recognized as the main pore-forming subunit of SOCC in the plasma membrane. Orai proteins alone can form highly Ca²⁺ selective SOCC channels. Also, members of the Transient Receptor Potential Canonical (TRPC) channel family are proposed to form heteromeric complexes with Orai1 subunits, forming SOCC with low Ca²⁺ selectivity. Recently, Ca²⁺ entry through SOCC, known as store-operated Ca²⁺ entry (SOCE), was identified in glomerular mesangial cells, tubular epithelium, and renovascular smooth muscle cells. The physiological and pathological relevance and the characterization of SOCC complexes in those cells are still unclear. In this review, we summarize the current knowledge of SOCC and their roles in renal glomerular, tubular and vascular cells, including studies from our laboratory, emphasizing SOCE regulation of fibrotic protein deposition. Understanding the diverse roles of SOCE in different renal cell types is essential, as SOCC and its signaling pathways are emerging targets for treatment of SOCE-related diseases.

Resveratrol alleviates inflammatory injury and enhances the apoptosis of fibroblast‑like synoviocytes via mitochondrial dysfunction and ER stress in rats with adjuvant arthritis

Resveratrol, a bioactive compound predominantly found in grapes and red wine, provides a wide range of properties that are beneficial for health, including anticancer and anti-inflammatory activities. Previously published studies have addressed the potential therapeutic effects of resveratrol on rheumatoid arthritis (RA); however, the subcellular mechanism remains to be fully elucidated. In the present study, the therapeutic effects of resveratrol on adjuvant arthritis (AA) in Sprague-Dawley rats were investigated, and the mechanisms of resveratrol-induced apoptosis in fibroblast-like synoviocytes (FLSs) were further examined. Based on the findings, resveratrol treatment over a 12-day period led to a reduction in paw swelling and arthritis scores at the macroscopic level, and an attenuation of inflammatory cell infiltration and synovial hyperplasia, upon a histopathological examination of the AA rats. Furthermore, the administration of resveratrol triggered decreases in the expression of interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor-α (TNF-α) and an increase in the expression of IL-10, alleviating inflammatory injury in AA rats in a dose-dependent manner. In addition, resveratrol was revealed to induce the apoptosis of FLSs when administered with 5 µM H₂O₂ as determined by elevated levels of Bax, caspase-3, caspase-12 and C/EBP-homologous protein, and the downregulation of B-cell lymphoma 2 (Bcl-2), suggesting that resveratrol is able to induce apoptosis in FLSs via the mitochondrial pathway and endoplasmic reticulum (ER) stress in a milieu containing 5 µM H₂O₂. Furthermore, JC-1 was used as a fluorescent probe to detect the mitochondrial membrane potential (Δψm), and resveratrol was shown to reduce the Δψm in FLSs in the presence of 5 µM H₂O₂. However, resveratrol was not able to trigger intracellular calcium overload, although it did suppress ATP- and thapsigargin-induced calcium release from the ER. In conclusion, the present study revealed that resveratrol was able to alleviate inflammatory injury in AA rats, triggering the apoptosis of FLSs via the mitochondrial pathway and ER stress. These results provide a theoretical basis for future treatments using resveratrol for RA.

AMP-Activated Protein Kinase (AMPK)-Dependent Regulation of Renal Transport

AMP-activated kinase (AMPK) is a serine/threonine kinase that is expressed in most cells and activated by a high cellular AMP/ATP ratio (indicating energy deficiency) or by Ca²⁺. In general, AMPK turns on energy-generating pathways (e.g., glucose uptake, glycolysis, fatty acid oxidation) and stops energy-consuming processes (e.g., lipogenesis, glycogenesis), thereby helping cells survive low energy states. The functional element of the kidney, the nephron, consists of the glomerulus, where the primary urine is filtered, and the proximal tubule, Henle's loop, the distal tubule, and the collecting duct. In the tubular system of the kidney, the composition of primary urine is modified by the reabsorption and secretion of ions and molecules to yield final excreted urine. The underlying membrane transport processes are mainly energy-consuming (active transport) and in some cases passive. Since active transport accounts for a large part of the cell's ATP demands, it is an important target for AMPK. Here, we review the AMPK-dependent regulation of membrane transport along nephron segments and discuss physiological and pathophysiological implications.

K15 Protein of Kaposi's Sarcoma Herpesviruses Increases Endothelial Cell Proliferation and Migration through Store-Operated Calcium Entry

Kaposi's sarcoma (KS) is a tumor of the vascular endothelium that is caused by Kaposi's sarcoma-associated herpesvirus (KSHV). K15 of KSHV is a specific gene encoding a transmembrane protein. Two highly different forms of K15, the predominant (K15P) and minor (K15M) have been identified in different KSHV strains. In genomic locations and protein topology, two K15 alleles resemble the latent membrane protein (LMP) 1 and LMP2A of Epstein⁻Barr virus. Both K15 proteins have motifs similar to those found in LMP1 and LMP2A. K15 therefore seems to be a hybrid of a distant evolutionary relative of LMP1 and LMP2A. Ca²⁺ is a second messenger and participates in numerous activities in cells, like proliferation, migration and metastasis. It has been found previously that LMP1 increased Ca²⁺ influx through store-operated calcium channels and blockade of LMP1 reduced store-operated Ca²⁺ entry (SOCE). LMP2A has similar activity. So we sought to determine whether K15 had similar activity. We showed that K15P induced Ca²⁺ influx and enhanced expression of Orail1, which is a vital protein in SOCE, and overexpression of K15P improved cell motility. Mutant K15P did not show these activities in HEK-293T and EA.hy 926 cells. Our results showed that K15P increased cell proliferation and migration though SOCE and established a novel mechanism for the development of KS and KSHV-associated diseases.

Short-term high-glucose treatment decreased abundance of Orai1 protein through posttranslational mechanisms in rat mesangial cells

The short-term effect of high-glucose (HG) treatment on store-operated Ca²⁺ entry in mesangial cells (MCs) is not well-known. The aim of the present study was to determine whether and how HG treatment for a short period altered protein abundance of Orai1, the channel mediating store-operated Ca²⁺ entry in MCs. Rat and human MCs were exposed to HG (25 mM) for 2, 4, 8, and 24 h, and the abundance of Orai1 protein was significantly decreased at the time points of 8 and 16 h. Consistently, HG treatment for 8 h significantly reduced store-operated Ca²⁺ entry in rat MCs. However, HG treatment for the same time periods did not alter the levels of Orai1 transcript. Cycloheximide, a protein synthesis inhibitor, did not affect the HG-induced decrease of Orai1 protein, suggesting a posttranslational mechanism was involved. However, the HG effect on Orai1 protein was significantly attenuated by MG132 (a ubiquitin-proteasome inhibitor) and NH₄Cl (a lysosomal pathway inhibitor). Furthermore, HG treatment for 8 h stimulated ubiquitination of Orai1 protein. We further found that polyethylene glycol-catalase, an antioxidant, significantly blunted the HG-induced reduction of Orai1 protein. In support of involvement of reactive oxygen species in the HG effects, hydrogen peroxide (H₂O₂) itself significantly decreased abundance of Orai1 protein and increased the level of ubiquitinated Orai1. Taken together, these results suggest that a short-term HG treatment decreased abundance of Orai1 protein in MCs by promoting the protein degradation through the ubiquitination-proteasome and -lysosome mechanisms. This HG-stimulated posttranslational mechanism was mediated by H₂O₂.

Contrasting Patterns of Agonist-induced Store-operated Ca2+ Entry and Vasoconstriction in Mesenteric Arteries and Aorta With Aging

Ca is a crucial factor in the regulation of smooth muscle contraction. Store-operated Ca entry (SOCE) is one pathway that mediates Ca influx and smooth muscle contraction. Vessel contraction function usually alters with aging to cause severe vascular-related diseases. However, the underlying mechanism is still not fully understood. Here, we assessed intracellular Ca and vessel tension and found that SOCE and SOCE-mediated contraction of vascular smooth muscle cells (VSMCs) was reduced in aorta but increased in mesenteric arteries from aged rats. The results of Western blot and immunofluorescence staining show that the expression levels of Orai1, a store-operated Ca channel, were increased in VSMCs of mesenteric arteries but were reduced in VSMCs of aorta with aging. In conclusion, we demonstrated that the changing pattern of SOCE and SOCE-mediated contraction of VSMCs is completely reversed in mesenteric arteries and aorta with aging, providing a potential therapeutic target for clinical treatment in age-related vascular diseases.

Blockade of Orai1 Store-Operated Calcium Entry Protects against Renal Fibrosis

Evidence supports an important role of Ca²⁺ release-activated Ca²⁺ channel protein 1 (Orai1)-mediated Ca²⁺ entry in the development of renal fibrosis, a common pathologic feature of CKDs that lead to ESRD, but the molecular mechanisms remain unclear. We determined the role of Orai1 calcium channel in renal fibrosis induced by high-fat diet and by unilateral ureteral obstruction. Mouse kidneys with fibrosis had higher levels of Orai1 protein expression than did kidneys without fibrosis. In vivo knockdown of Orai1 with adenovirus harboring Orai1-short hairpin RNA or inhibition of Orai1 with SKF96365 dramatically prevented renal fibrosis and significantly decreased protein expression of fibronectin, α‑smooth muscle actin, and TGF‑β1 in the kidney cortex of ApoE^-/- mice on a high-fat diet and in the obstructed kidneys of mice with unilateral ureteral obstruction. Compared with kidney biopsy specimens of patients with glomerular minimal change disease, those of patients with fibrotic nephropathy had higher expression levels of Orai1. In cultured human proximal tubule epithelial cells (HK2), knockdown of Orai1 Ca²⁺ channel with adenovirus-Orai1-short hairpin RNA markedly inhibited TGF-β1-induced intracellular Ca²⁺ influx and phosphorylation of smad2/3. Knockdown or blockade of the Orai1 Ca²⁺ channel in HK2 cells also prevented epithelial-to-mesenchymal transition induced by TGF‑β1. In conclusion, blockade of the Orai1 Ca²⁺ channel prevented progression of renal fibrosis in mice, likely by suppressing smad2/3 phosphorylation and TGF-β1-induced epithelial-to-mesenchymal transition. These results render the Orai1 Ca²⁺ channel a potential therapeutic target against renal fibrosis.

Knockdown of CLIC4 enhances ATP-induced HN4 cell apoptosis through mitochondrial and endoplasmic reticulum pathways

Background

Human head and neck squamous carcinoma is the 6th most prevalent carcinoma worldwide. Although many novel therapies have been developed, the clinical treatment for patients remains non-ideal. Chloride intracellular channel 4 (CLIC4), one of the seven members of the CLIC family, is a newly found Cl⁻ channel that participates in various biological processes, including cellular apoptosis and differentiation. Accumulating evidence has revealed the significant role of CLIC4 in regulating the apoptosis of different cancer cells. Here, we investigated the functional role of CLIC4 in the apoptosis of HN4 cells, a human head and neck squamous carcinoma cell line.

Results

In the present study, we used immunohistochemical staining to demonstrate that the expression level of CLIC4 is elevated in the tissue of human oral squamous carcinoma compared with healthy human gingival tissue. Specific CLIC4 small interfering RNA was used to knockdown the expression of CLIC4. The results showed that knockdown of CLIC4 with or without 100 μM adenosine triphosphate (ATP) treatment significantly increased the expression of Bax, active caspase 3, active caspase 4 and CHOP but suppressed Bcl-2 expression in HN4 cells. Moreover, the results from the TdT-mediated dUTP nick end labeling assay indicated that CLIC4 knockdown induced a higher apoptotic rate in HN4 cells under the induction of ATP. In addition, knockdown of CLIC4 dramatically enhanced ATP-induced mitochondrial membrane depolarization in HN4 cells. Moreover, intracellular Ca²⁺ measurement revealed that Ca²⁺ release induced by ATP and thapsigargin, a Ca²⁺-ATPase inhibitor of the endoplasmic reticulum, was significantly enhanced by the suppression of CLIC4 in HN4 cells.

Conclusions

Knockdown of CLIC4 enhanced ATP-induced apoptosis in HN4 cells. Both the pathways of mitochondria and endoplasmic reticulum stress were involved in CLIC4-mediated cell apoptosis. Based on our finding, CLIC4 may be a potential and valuable target for the clinical treatment of head and neck squamous carcinoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0070-1) contains supplementary material, which is available to authorized users.

Ca(2+) dynamics in oocytes from naturally-aged mice

The ability of human metaphase-II arrested eggs to activate following fertilisation declines with advancing maternal age. Egg activation is triggered by repetitive increases in intracellular Ca²⁺ concentration ([Ca²⁺]_i) in the ooplasm as a result of sperm-egg fusion. We therefore hypothesised that eggs from older females feature a reduced ability to mount appropriate Ca²⁺ responses at fertilisation. To test this hypothesis we performed the first examination of Ca²⁺ dynamics in eggs from young and naturally-aged mice. Strikingly, we find that Ca²⁺ stores and resting [Ca²⁺]_i are unchanged with age. Although eggs from aged mice feature a reduced ability to replenish intracellular Ca²⁺ stores following depletion, this difference had no effect on the duration, number, or amplitude of Ca²⁺ oscillations following intracytoplasmic sperm injection or expression of phospholipase C zeta. In contrast, we describe a substantial reduction in the frequency and duration of oscillations in aged eggs upon parthenogenetic activation with SrCl₂. We conclude that the ability to mount and respond to an appropriate Ca²⁺ signal at fertilisation is largely unchanged by advancing maternal age, but subtle changes in Ca²⁺ handling occur that may have more substantial impacts upon commonly used means of parthenogenetic activation.

Impairment of hepatic nuclear factor-4α binding to the Stim1 promoter contributes to high glucose-induced upregulation of STIM1 expression in glomerular mesangial cells

The present study was carried out to investigate if hepatic nuclear factor (HNF)4α contributed to the high glucose-induced increase in stromal interacting molecule (STIM)1 protein abundance in glomerular mesangial cells (MCs). Western blot and immunofluorescence experiments showed HNF4α expression in MCs. Knockdown of HNF4α using a small interfering RNA approach significantly increased mRNA expression levels of both STIM1 and Orai1 and protein expression levels of STIM1 in cultured human MCs. Consistently, overexpression of HNF4α reduced expressed STIM1 protein expression in human embryonic kidney-293 cells. Furthermore, high glucose treatment did not significantly change the abundance of HNF4α protein in MCs but significantly attenuated HNF4α binding activity to the Stim1 promoter. Moreover, knockdown of HNF4α significantly augmented store-operated Ca(2+) entry, which is known to be gated by STIM1 and has recently been found to be antifibrotic in MCs. In agreement with those results, knockdown of HNF4α significantly attenuated the fibrotic response of high glucose. These results suggest that HNF4α negatively regulates STIM1 transcription in MCs. High glucose increases STIM1 expression levels by impairing HNF4α binding activity to the Stim1 promoter, which subsequently releases Stim1 transcription from HNF4α repression. Since the STIM1-gated store-operated Ca(2+) entry pathway in MCs has an antifibrotic effect, inhibition of HNF4α in MCs might be a potential therapeutic option for diabetic kidney disease.

Increased TRPP2 expression in vascular smooth muscle cells from high-salt intake hypertensive rats: The crucial role in vascular dysfunction

SCOPE

High-salt intake is a major risk factor in the development of hypertension. The underlying mechanism of high sodium on the cardiovascular system has received extensive attention. TRPP2 (Polycystin-2) is a Ca(2+) permeable nonselective cation channel that mediates Ca(2+) mobilization to control vascular smooth muscle cells (VSMCs) contraction. Here, we investigated TRPP2 expression change in VSMCs from high-salt intake hypertensive rats and role of TRPP2 in the development of high-salt diet-induced hypertension.

METHODS AND RESULTS

After 4 ws of dietary treatment, systolic blood pressure was significantly elevated in high-salt intake rats (132 ± 3 mmHg) compared with regular diet control rats (104 ± 2 mmHg). Results from vessel tension and diameter measurements show that high-salt intake potentiated phenylephrine-induced contraction in denuded mesenteric artery and thoracic aorta. Immunoblot and immunofluorescence data indicate that TRPP2 expression in VSMCs from mesenteric artery and thoracic aorta was significantly increased in high-salt intake-induced hypertensive rats. However, agonist-induced contractions in denuded mesenteric artery and thoracic aorta were markedly decreased if TRPP2 was knocked down by specific shRNA.

CONCLUSION

Our data demonstrate that high-salt intake increased TRPP2 expression in VSMCs, which in turn potentiated blood vessel response to contractors; this may participate in the development of hypertension.