Association Analysis of the Reticulon 1 Gene in End-Stage Kidney Disease

RTN1A mediates diabetes-induced AKI-to-CKD transition

Diabetic patients have increased susceptibility to acute kidney injury (AKI), and AKI could progress to chronic tubulointerstitial injury and fibrosis, referred to as AKI-to-chronic kidney disease (AKI-to-CKD) transition. However, whether diabetes directly promotes AKI-to-CKD transition is not known. We previously showed that reticulon-1A (RTN1A), a gene highly upregulated in injured renal tubular epithelial cells (RTECs), promotes AKI-to-CKD transition in nondiabetic settings. Therefore, we also examined whether reducing RTN1A expression could attenuate diabetes-induced AKI-to-CKD transition. Diabetes was induced by a high-fat diet and streptozotocin injections, and unilateral ischemic reperfusion injury was created as an AKI model in control, diabetic, and RTEC-specific Rtn1a-knockdown diabetic mice. AKI induced greater renal function decline, tubulointerstitial injury, and fibrosis in diabetic mice than in nondiabetic mice. Reduction of RTN1A markedly reduced the CKD development following AKI in diabetic mice, which was associated with reduced ER stress and mitochondrial dysfunction in RTECs. These findings indicate that diabetes markedly accelerates AKI-to-CKD transition and that RTN1A is a crucial mediator of diabetes-induced AKI-to-CKD transition. The development of RTN1A inhibitors could potentially attenuate AKI-to-CKD transition in diabetic patients.

RTN3 deficiency exacerbates cisplatin-induced acute kidney injury through the disruption of mitochondrial stability

Reticulum 3 (RTN3) is an endoplasmic reticulum (ER) protein that has been reported to act in neurodegenerative diseases and lipid metabolism. However, the role of RTN3 in acute kidney injury (AKI) has not been explored. Here, we employed public datasets, patient data, and animal models to explore the role of RTN3 in AKI. The underlying mechanisms were studied in primary renal tubular epithelial cells and in the HK2 cell line. We found reduced expression of RTN3 in AKI patients, cisplatin-induced mice, and cisplatin-treated HK2 cells. RTN3-null mice exhibit more severe AKI symptoms and kidney fibrosis after cisplatin treatment. Mitochondrial dysfunction was also found in cells with RTN3 knockdown or knockout. A mechanistic study revealed that RTN3 can interact with HSPA9 in kidney cells. RTN3 deficiency may disrupt the RTN3-HSPA9-VDAC2 complex and affect MAMs during ER-mitochondrion contact, which further leads to mitochondrial dysfunction and exacerbates cisplatin-induced AKI. Our study indicated that RTN3 was important in the kidney and that a decrease in RTN3 in the kidney might be a risk factor for the aggravation of AKI.

Reticulon-1A mediates diabetic kidney disease progression through endoplasmic reticulum-mitochondrial contacts in tubular epithelial cells

Recent epidemiological studies suggest that some patients with diabetes progress to kidney failure without significant albuminuria and glomerular injury, suggesting a critical role of kidney tubular epithelial cell (TEC) injury in diabetic kidney disease (DKD) progression. However, the major risk factors contributing to TEC injury and progression in DKD remain unclear. We previously showed that expression of endoplasmic reticulum-resident protein Reticulon-1A (RTN1A) increased in human DKD, and the increased RTN1A expression promoted TEC injury through endoplasmic reticulum (ER) stress response. Here, we show that TEC-specific RTN1A overexpression worsened DKD in mice, evidenced by enhanced tubular injury, tubulointerstitial fibrosis, and kidney function decline. But RTN1A overexpression did not exacerbate diabetes-induced glomerular injury or albuminuria. Notably, RTN1A overexpression worsened both ER stress and mitochondrial dysfunction in TECs under diabetic conditions by regulation of ER-mitochondria contacts. Mechanistically, ER-bound RTN1A interacted with mitochondrial hexokinase-1 and the voltage-dependent anion channel-1 (VDAC1), interfering with their association. This disengagement of VDAC1 from hexokinase-1 resulted in activation of apoptotic and inflammasome pathways, leading to TEC injury and loss. Thus, our observations highlight the importance of ER-mitochondrial crosstalk in TEC injury and the salient role of RTN1A-mediated ER-mitochondrial contact regulation in DKD progression.

Genetics, Genomics, and Precision Medicine in End-Stage Kidney Disease

Recent advances in genetics of renal disease have deepened our understanding of progressive kidney disease. Here, we review genetic variants that are of particular importance to progressive glomerular disease that result in end-stage kidney disease (ESKD). Some of the most striking findings relate to APOL1 genetic variants, seen exclusively in individuals of sub-Saharan African descent, that create a predisposition to particular renal disorders, including focal segmental glomerulosclerosis and arterionephrosclerosis. We also review the genetics of cardiovascular disease in ESKD and note that little work has been published on the genetics of other ESKD complications, including anemia, bone disease, and infections. Deeper understanding of the genetics of ESKD and its complications may lead to new therapies that are tailored to an individual patient's genetic profile or are discovered based on genetic approaches that identify novel pathways of renal cell injury and repair.

Endoplasmic reticulum stress in the pathogenesis of fibrotic disease

Eukaryotic cells contain an elegant protein quality control system that is crucial in maintaining cellular homeostasis; however, dysfunction of this system results in endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). Severe or prolonged ER stress is associated with the development of degenerative and fibrotic disorders in multiple organs, as evidenced by the identification of disease-causing mutations in epithelial-restricted genes that lead to protein misfolding or mistrafficking in familial fibrotic diseases. Emerging evidence implicates ER stress and UPR signaling in a variety of profibrotic mechanisms in individual cell types. In epithelial cells, ER stress can induce apoptosis, inflammatory signaling, and epithelial-mesenchymal transition. In other cell types, ER stress is linked to myofibroblast activation, macrophage polarization, and T cell differentiation. ER stress-targeted therapies have begun to emerge using approaches that range from global enhancement of chaperone function to selective targeting of activated ER stress sensors and other downstream mediators. As the complex regulatory mechanisms of this system are further clarified, there are opportunities to develop new disease-modifying therapeutic strategies in a wide range of chronic fibrotic diseases.

Gene networks in neurodegenerative disorders

Three neurodegenerative diseases [Amyotrophic Lateral Sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD)] have many characteristics like pathological mechanisms and genes. In this sense some researchers postulate that these diseases share the same alterations and that one alteration in a specific protein triggers one of these diseases. Analyses of gene expression may shed more light on how to discover pathways, pathologic mechanisms associated with the disease, biomarkers and potential therapeutic targets. In this review, we analyze four microarrays related to three neurodegenerative diseases. We will systematically examine seven genes (CHN1, MDH1, PCP4, RTN1, SLC14A1, SNAP25 and VSNL1) that are altered in the three neurodegenerative diseases. A network was built and used to identify pathways, miRNA and drugs associated with ALS, AD and PD using Cytoscape software an interaction network based on the protein interactions of these genes. The most important affected pathway is PI3K-Akt signalling. Thirteen microRNAs (miRNA-19B1, miRNA-107, miRNA-124-1, miRNA-124-2, miRNA-9-2, miRNA-29A, miRNA-9-3, miRNA-328, miRNA-19B2, miRNA-29B2, miRNA-124-3, miRNA-15A and miRNA-9-1) and four drugs (Estradiol, Acetaminophen, Resveratrol and Progesterone) for new possible treatments were identified.

The Role of Endoplasmic Reticulum Stress in Diabetic Nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy (DN) has become the leading cause of end-stage renal disease (ESRD) worldwide. Accumulating evidence suggests that endoplasmic reticulum (ER) stress plays a major role in the development and progression of DN. Recent findings suggested that many attributes of DN, such as hyperglycemia, proteinuria, and increased advanced glycation end products and free fatty acids, can all trigger unfolded protein response (UPR) in kidney cells. Herein, we review the current knowledge on the role of ER stress in the setting of kidney injury with a specific emphasis on DN.

RECENT FINDINGS

As maladaptive ER stress response caused by excessively prolonged UPR will eventually cause cell death and increase kidney injury, several ER stress inhibitors have been shown to improve DN in animal models, albeit blocking both adaptive and maladaptive UPR. More recently, reticulon-1A (RTN1A), an ER-associated protein, was shown to be increased in both human and mouse diabetic kidneys. Its expression correlates with the progression of DN, and its polymorphisms are associated with kidney disease in people with diabetes. Increased RTN1A expression heightened the ER stress response and renal cell apoptosis, and conversely reduced RTN1A in renal cells decreased apoptosis and ameliorated kidney injury and DN progression, suggesting that RTN1A may be a novel target to specifically restrain the maladaptive UPR. These findings suggest that ER stress response in renal cells is a key driver of progression of DN and that the inhibition of the unchecked ER stress response in DN, such as by inhibition of RTN1A function, may be a promising therapeutic approach against DN.

Association of Chemerin and Vascular Endothelial Growth Factor (VEGF) with Diabetic Nephropathy

Background

Diabetic nephropathy (DN) is a common complication of diabetes, caused by diabetic microvascular lesions. The pathogenesis of DN is complicated, involving genetics, physics, chemistry, and environmental factors. Chemerin is a fat cell factor that participates in regulating inflammation. Vascular endothelial growth factor (VEGF) promotes vascular endothelial cell proliferation, differentiation, and angiogenesis. The relationship role of Chemerin and VEGF in DN is not fully understood.

Material/Methods

SD rats were randomly divided into 2 groups: the control group and the DN group. Streptozotocin was used to construct the DN model. Serum creatinine (Scr), blood urea nitrogen (BUN), and urine microalbumin (UAlb) were detected. Real-time PCR and Western blot were used to test Chemerin and VEGF mRNA and protein expression in kidney tissue. ELISA was performed to test TGF-β1, TNF-α, and INF-γ levels. The correlation of Chemerin and VEGF with renal function and inflammatory factors was analyzed.

Results

DN group rats showed obviously increased Scr and BUN levels, and elevated TGF-β1, TNF-α, and INF-γ secretion (P<0.05). Compared with controls, Chemerin and VEGF were clearly overexpressed in the DN group (P<0.05). Chemerin and VEGF expression were positively correlated with inflammatory factors and renal function.

Conclusions

Chemerin and VEGF play important roles in DN by regulating inflammatory factors and renal function. They may be treated as indicators of DN.