Na+/H+ exchanger-1 reduces podocyte injury caused by endoplasmic reticulum stress via autophagy activation

Crocin improves the renal autophagy in rat experimental membranous nephropathy via regulating the SIRT1/Nrf2/HO-1 signaling pathway

Membranous nephropathy (MN) is a glomerular disease. Crocin is isolated from saffron and gardenia. Its antioxidant, anti-inflammatory, anti-hyperlipidemic, anti-atherosclerotic, anti-tumor, free-radical scavenging and neuroprotective activities have been well established. We investigated the biological functions of crocin and its related mechanisms in MN. We established an experimental passive Heymann nephritis (PHN) rat model induced by anti-Fx1A antiserum. The rats were divided into sham, sham + crocin, PHN, PHN + crocin, and PHN + enalapril groups. Blood samples and kidneys of rats were collected for estimation of biochemical parameters in serum and oxidative stress indicators in kidney tissues. Histopathological changes of renal tissues were evaluated by hematoxylin and eosin, periodic acid-Schiff (PAS) and Masson staining. The podocyte number was estimated by immunohistochemistry staining of Wilms tumor type 1 (WT1). The deposition of rat anti-rabbit IgG antibodies, complement C3 and C5b-9 was detected by immunofluorescence staining. Western blotting was performed to measure the levels of Sirtuin 1 (Sirt1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1) and apoptosis-related proteins. The total cholesterol, triglycerides, creatinine, blood urea nitrogen, urine volume and urine albumin of PMN rats were significantly reduced by crocin. Additionally, crocin attenuated the renal histopathological changes. Moreover, the oxidative stress damage and podocyte loss and immune injury were relieved by crocin in PHN rats. Mechanistically, crocin administration activated the Sirt1/Nrf2/HO-1 pathways. The results provide a scientific basis that crocin could alleviate MN by inhibiting immune injury and podocyte damage through activating the Sirt1/Nrf2/HO-1 pathways.

The IRE1α pathway in glomerular diseases: The unfolded protein response and beyond

Endoplasmic reticulum (ER) function is vital for protein homeostasis ("proteostasis"). Protein misfolding in the ER of podocytes (glomerular visceral epithelial cells) is an important contributor to the pathogenesis of human glomerular diseases. ER protein misfolding causes ER stress and activates a compensatory signaling network called the unfolded protein response (UPR). Disruption of the UPR, in particular deletion of the UPR transducer, inositol-requiring enzyme 1α (IRE1α) in mouse podocytes leads to podocyte injury and albuminuria in aging, and exacerbates injury in glomerulonephritis. The UPR may interact in a coordinated manner with autophagy to relieve protein misfolding and its consequences. Recent studies have identified novel downstream targets of IRE1α, which provide new mechanistic insights into proteostatic pathways. Novel pathways of IRE1α signaling involve reticulophagy, mitochondria, metabolism, vesicular trafficking, microRNAs, and others. Mechanism-based therapies for glomerulopathies are limited, and development of non-invasive ER stress biomarkers, as well as targeting ER stress with pharmacological compounds may represent a therapeutic opportunity for preventing or attenuating progression of chronic kidney disease.

Podocyte Autophagy in Homeostasis and Disease

Autophagy is a protective mechanism that removes dysfunctional components and provides nutrition for cells. Podocytes are terminally differentiated specialized epithelial cells that wrap around the capillaries of the glomerular filtration barrier and show high autophagy level at the baseline. Here, we provide an overview of cellular autophagy and its regulation in homeostasis with specific reference to podocytes. We discuss recent data that have focused on the functional role and regulation of autophagy during podocyte injury in experimental and clinical glomerular diseases. A thorough understanding of podocyte autophagy could shed novel insights into podocyte survival mechanisms with injury and offer potential targets for novel therapeutics for glomerular disease.

Curcumin Improves the Renal Autophagy in Rat Experimental Membranous Nephropathy via Regulating the PI3K/AKT/mTOR and Nrf2/HO-1 Signaling Pathways

Membranous nephropathy (MN, also known as membranous glomerulopathy) is one of the many glomerular diseases causing nephrotic syndrome. The literature indicates that autophagy is associated with the homeostasis of podocytes in glomeruli. Curcumin, the main active component in turmeric, has drawn attention for its effective bioactivities against chronic kidney disease. The current study was aimed at assessing the effects of curcumin and exploring the underlying mechanism that mediates autophagy in an animal model of passive Heymann nephritis (PHN) in rats. Passive Heymann nephritis (PHN) was induced in male SD rats by intraperitoneal injection of anti-Fx1A serum. The rats were divided into 3 groups: control (n = 10, normal diet), model group (n = 10, 0.5% sodium carboxymethylcellulose), and curcumin (n = 10, 300 mg/kg/d). The kidney function and oxidative stress indicators were measured using commercial diagnostic kits, and the histomorphology of renal tissues was observed. The number of podocytes was measured by immunohistochemistry. Meanwhile, the autophagosomes in podocyte were analyzed by transmission electron microscopy and the immunofluorescence assay pointing to p62, an autophagic marker. Western blot analyzed the levels of apoptosis, autophagy, PI3K/AKT/mTOR, and Nrf2/HO-1 pathway-associated proteins. The total cholesterol (TC), triglycerides (TG), creatinine (Scr), blood urea nitrogen (BUN), urine volume, and urine albumin of PHN rats were significantly reduced by the administration of curcumin and attenuated renal histomorphological changes in model rats. Meanwhile, curcumin improved the oxidative stress response by decreasing MDA and increasing SOD, GSH, and CAT levels in the kidney of PHN rats. Furthermore, curcumin significantly ameliorated the podocyte loss, along with the fusion, and increased the autophagic vacuoles compared to the PHN control rats. In addition, curcumin downregulated the expression of Bax, Caspase-3, p62, PI3K, p-AKT, and p-mTOR proteins and upregulated the Bcl-2, beclin1, LC3, Nrf2, and HO-1 levels in this animal model. The results provide a scientific basis that curcumin could significantly alleviate the development of MN by inducing autophagy and alleviating renal oxidative stress through the PI3K/AKT/mTOR and Nrf2/HO-1 pathways.

Inhibiting Autophagy in Renal Cell Cancer and the Associated Tumor Endothelium

The clear cell subtype of kidney cancer encompasses most renal cell carcinoma cases and is associated with the loss of von Hippel-Lindau gene function or expression. Subsequent loss or mutation of the other allele influences cellular stress responses involving nutrient and hypoxia sensing. Autophagy is an important regulatory process promoting the disposal of unnecessary or degraded cellular components, tightly linked to almost all cellular processes. Organelles and proteins that become damaged or that are no longer needed in the cell are sequestered and digested in autophagosomes upon fusing with lysosomes, or alternatively, released via vesicular exocytosis. Tumor development tends to disrupt the regulation of the balance between this process and apoptosis, permitting prolonged cell survival and increased replication. Completed trials of autophagic inhibitors using hydroxychloroquine in combination with other anticancer agents including rapalogues and high-dose interleukin 2 have now been reported. The complex nature of autophagy and the unique biology of clear cell renal cell carcinoma warrant further understanding to better develop the next generation of relevant anticancer agents.

Sodium hydrogen exchanger 9 NHE9 (SLC9A9) and its emerging roles in neuropsychiatric comorbidity

Variations in SLC9A9 gene expression and protein function are associated with multiple human diseases, which range from Attention-deficit/hyperactivity disorder (ADHD) to glioblastoma multiforme. In an effort to determine the full spectrum of human disease associations with SLC9A9, we performed a systematic review of the literature. We also review SLC9A9's biochemistry, protein structure, and function, as well as its interacting partners with the goal of identifying mechanisms of disease and druggable targets. We report gaps in the literature regarding the genes function along with consistent trends in disease associations that can be used to further research into treating the respective diseases. We report that SLC9A9 has strong associations with neuropsychiatric diseases and various cancers. Interestingly, we find strong overlap in SLC9A9 disease associations and propose a novel role for SLC9A9 in neuropsychiatric comorbidity. In conclusion, SLC9A9 is a multifunctional protein that, through both its endosome regulatory function and its protein-protein interaction network, has the ability to modulate signaling axes, such as the PI3K pathway, among others.

Matrix-assisted laser desorption/ionization mass spectrometry imaging to uncover protein alterations associated with the progression of IgA nephropathy

IgA nephropathy (IgAN) is one of the most diffuse glomerulonephrites worldwide, and many issues still remain regarding our understanding of its pathogenesis. The disease is diagnosed by renal biopsy examination, but potential pitfalls still persist with regard to discriminating its primary origin and, as a result, determining patient outcome remains challenging. In this pilot study, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) was performed on renal biopsies obtained from patients with IgAN (n = 11) and other mesangioproliferative glomerulonephrites (MesPGN, n = 6) in order to enlighten proteomic alterations that may be associated with the progression of IgAN. Differences in the proteomic profiles of IgAN and MesPGN tissue could clearly be detected using this approach and, furthermore, 14 signals (AUC ≥ 0.8) were observed to have an altered intensity among the different CKD stages within the IgAN group. In particular, large increases in the intensity of these signals could be observed at CKD stages II and above. These signals primarily corresponded to proteins involved in either inflammatory and healing pathways and their increased intensity was localized within regions of tissue with large amounts of inflammatory cells or sclerosis. Despite much work in recent years, our molecular understanding of IgAN progression remains incomplete. This pilot study represents a promising starting point in the search for novel protein markers that can assist clinicians in better understanding the pathogenesis of IgAN and highlighting those patients who may progress to end-stage renal disease.

The role of autophagy in the pathogenesis of exposure keratitis

Incomplete tear film spreading and eyelid closure can cause defective renewal of the ocular surface and air exposure-induced epithelial keratopathy (EK). In this study, we characterized the role of autophagy in mediating the ocular surface changes leading to EK. Human corneal epithelial cells (HCECs) and C57BL/6 mice were employed as EK models, respectively. Transmission electron microscopy (TEM) evaluated changes in HCECs after air exposure. Each of these models was treated with either an autophagy inhibitor [chloroquine (CQ) or 3-methyladenine (3-MA)] or activator [Rapamycin (Rapa)]. Immunohistochemistry assessed autophagy-related proteins, LC3 and p62 expression levels. Western blotting confirmed the expression levels of the autophagy-related proteins [Beclin1 and mammalian target of rapamycin (mTOR)], the endoplasmic reticulum (ER) stress-related proteins (PERK, eIF2α and CHOP) and the PI3K/Akt/mTOR signalling pathway-related proteins. Real-time quantitative PCR (qRT-PCR) determined IL-1β, IL-6 and MMP9 gene expression levels. The TUNEL assay detected apoptotic cells. TEM identified autophagic vacuoles in both EK models. Increased LC3 puncta formation and decreased p62 immunofluorescent staining and Western blotting confirmed autophagy induction. CQ treatment increased TUNEL positive staining in HCECs, while Rapa had an opposite effect. Similarly, CQ injection enhanced air exposure-induced apoptosis and inflammation in the mouse corneal epithelium, which was inhibited by Rapa treatment. Furthermore, the phosphorylation status of PERK and eIF2α and CHOP expression increased in both EK models indicating that ER stress-induced autophagy promoted cell survival. Taken together, air exposure-induced autophagy is indispensable for the maintenance of corneal epithelial physiology and cell survival.

Notoginsenoside R1 attenuates glucose-induced podocyte injury via the inhibition of apoptosis and the activation of autophagy through the PI3K/Akt/mTOR signaling pathway

Injury to terminally differentiated podocytes contributes ignificantly to proteinuria and glomerulosclerosis. The aim of this study was to examine the protective effects of notoginsenoside R1 (NR1) on the maintenance of podocyte number and foot process architecture via the inhibition of apoptosis, the induction of autophagy and the maintenance pf podocyte biology in target cells. The effects of NR1 on conditionally immortalized human podocytes under high glucose conditions were evaluated by determining the percentage apoptosis, the percentage autophagy and the expression levels of slit diaphragm proteins. Our results revealed that NR1 protected the podocytes against high glucose-induced injury by decreasing apoptosis, increasing autophagy and by promoting cytoskeletal recovery. The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway was further investigated in order to elucidate the mechanisms responsible for the protective effects of NR1 on podocytes. Our data indicated that treatment with NR increased the phosphorylation levels of PI3K, Akt and mTOR, leading to the activation of the PI3K/Akt/mTOR signaling pathway in podocytes. To the best of our knowledge, this is the first in vitro study to demonstrate that NR1 protects podocytes by activating the PI3K/Akt/mTOR pathway.

Role of Epithelial-Mesenchyme Transition in Chlamydia Pathogenesis

Chlamydia trachomatis genital infection in women causes serious adverse reproductive complications, and is a strong co-factor for human papilloma virus (HPV)-associated cervical epithelial carcinoma. We tested the hypothesis that Chlamydia induces epithelial-mesenchyme transition (EMT) involving T cell-derived TNF-alpha signaling, caspase activation, cleavage inactivation of dicer and dysregulation of micro-RNA (miRNA) in the reproductive epithelium; the pathologic process of EMT causes fibrosis and fertility-related epithelial dysfunction, and also provides the co-factor function for HPV-related cervical epithelial carcinoma. Using a combination of microarrays, immunohistochemistry and proteomics, we showed that chlamydia altered the expression of crucial miRNAs that control EMT, fibrosis and tumorigenesis; specifically, miR-15a, miR-29b, miR-382 and MiR-429 that maintain epithelial integrity were down-regulated, while miR-9, mi-R-19a, miR-22 and miR-205 that promote EMT, fibrosis and tumorigenesis were up-regulated. Chlamydia induced EMT in vitro and in vivo, marked by the suppression of normal epithelial cell markers especially E-cadherin but up-regulation of mesenchymal markers of pathological EMT, including T-cadherin, MMP9, and fibronectin. Also, Chlamydia upregulated pro-EMT regulators, including the zinc finger E-box binding homeobox protein, ZEB1, Snail1/2, and thrombospondin1 (Thbs1), but down-regulated anti-EMT and fertility promoting proteins (i.e., the major gap junction protein connexin 43 (Cx43), Mets1, Add1Scarb1 and MARCKSL1). T cell-derived TNF-alpha signaling was required for chlamydial-induced infertility and caspase inhibitors prevented both infertility and EMT. Thus, chlamydial-induced T cell-derived TNF-alpha activated caspases that inactivated dicer, causing alteration in the expression of reproductive epithelial miRNAs and induction of EMT. EMT causes epithelial malfunction, fibrosis, infertility, and the enhancement of tumorigenesis of HPV oncogene-transformed epithelial cells. These findings provide a novel understanding of the molecular pathogenesis of chlamydia-associated diseases, which may guide a rational prevention strategy.

Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule

The ubiquitously expressed plasma membrane Na(+)-H(+) exchanger NHE1 is a 12 transmembrane-spanning protein that directs important cell functions such as homeostatic intracellular volume and pH control. The 315 amino acid cytosolic tail of NHE1 binds plasma membrane phospholipids and multiple proteins that regulate additional, ion-translocation independent functions. This review focuses on NHE1 structure/function relationships, as well as the role of NHE1 in kidney proximal tubule functions, including pH regulation, vectorial Na(+) transport, cell volume control and cell survival. The implications of these functions are particularly critical in the setting of progressive, albuminuric kidney diseases, where the accumulation of reabsorbed fatty acids leads to disruption of NHE1-membrane phospholipid interactions and tubular atrophy, which is a poor prognostic factor for progression to end stage renal disease. This review amplifies the vital role of the proximal tubule NHE1 Na(+)-H(+) exchanger as a kidney cell survival factor.