Proteomic analysis of AQP11-null kidney: Proximal tubular type polycystic kidney disease

Mechanistic complement of autosomal dominant polycystic kidney disease: the role of aquaporins

Autosomal dominant polycystic kidney disease is a genetic kidney disease caused by mutations in the genes PKD1 or PKD2. Its course is characterized by the formation of progressively enlarged cysts in the renal tubules bilaterally. The basic genetic explanation for autosomal dominant polycystic kidney disease is the double-hit theory, and many of its mechanistic issues can be explained by the cilia doctrine. However, the precise molecular mechanisms underpinning this condition's occurrence are still not completely understood. Experimental evidence suggests that aquaporins, a class of transmembrane channel proteins, including aquaporin-1, aquaporin-2, aquaporin-3, and aquaporin-11, are involved in the mechanism of autosomal dominant polycystic kidney disease. Aquaporins are either a potential new target for the treatment of autosomal dominant polycystic kidney disease, and further study into the physiopathological role of aquaporins in autosomal dominant polycystic kidney disease will assist to clarify the disease's pathophysiology and increase the pool of potential treatment options. We primarily cover pertinent findings on aquaporins in autosomal dominant polycystic kidney disease in this review.

Abnormal expression and the significant prognostic value of aquaporins in clear cell renal cell carcinoma

Aquaporins (AQPs) are a kind of transmembrane proteins that exist in various organs of the human body. AQPs play an important role in regulating water transport, lipid metabolism and glycolysis of cells. Clear cell renal cell carcinoma (ccRCC) is a common malignant tumor of the kidney, and the prognosis is worse than other types of renal cell cancer (RCC). The impact of AQPs on the prognosis of ccRCC and the potential relationship between AQPs and the occurrence and development of ccRCC are demanded to be investigated. In this study, we first explored the expression pattern of AQPs by using Oncomine, UALCAN, and HPA databases. Secondly, we constructed protein-protein interaction (PPI) network and performed function enrichment analysis through STRING, GeneMANIA, and Metascape. Then a comprehensive analysis of the genetic mutant frequency of AQPs in ccRCC was carried out using the cBioPortal database. In addition, we also analyzed the main enriched biological functions of AQPs and the correlation with seven main immune cells. Finally, we confirmed the prognostic value of AQPs throughGEPIA and Cox regression analysis. We found that the mRNA expression levels of AQP0/8/9/10 were up-regulated in patients with ccRCC, while those of AQP1/2/3/4/5/6/7/11 showed the opposite. Among them, the expression differences of AQP1/2/3/4/5/6/7/8/9/11 were statistically significant. The differences in protein expression levels of AQP1/2/3/4/5/6 in ccRCC and normal renal tissues were consistent with the change trends of mRNA. The biological functions of AQPs were mainly concentrated in water transport, homeostasis maintenance, glycerol transport, and intracellular movement of sugar transporters. The high mRNA expression levels of AQP0/8/9 were significantly correlated with worse overall survival (OS), while those of AQP1/4/7 were correlated with better OS. AQP0/1/4/9 were prognostic-related factors, and AQP1/9 were independent prognostic factors. In general, this research has investigated the values of AQPs in ccRCC, which could become new survival markers for ccRCC targeted therapy.

Heterogeneity of cell composition and origin identified by single-cell transcriptomics in renal cysts of patients with autosomal dominant polycystic kidney disease

Rationale: Renal cysts in patients with autosomal dominant polycystic kidney disease (ADPKD) can originate from any nephron segments, including proximal tubules (PT), the loop of Henle (LOH), distal tubules (DT), and collecting ducts (CD). Previous studies mostly used limited cell markers and failed to identify cells negative for these markers. Therefore, the cell composition and origin of ADPKD cyst are still unclear, and mechanisms of cystogenesis of different origins await further exploration.

Methods: We performed single-cell RNA sequencing for the normal kidney tissue and seven cysts derived from superficial or deep layers of the polycystic kidney from an ADPKD patient.

Results: Twelve cell types were identified and analyzed. We found that a renal cyst could be derived either from CD or both PT and LOH. Gene set variation analysis (GSVA) showed that epithelial mesenchymal transition (EMT), TNFA signaling via the NFKB pathways, and xenobiotic metabolism were significantly activated in PT-derived cyst epithelial cells while robust expression of genes involved in G2M Checkpoint, mTORC1 signaling, E2F Targets, MYC Targets V1, MYC Targets V2 were observed in CD-derived cells.

Conclusion: Our results revealed that a single cyst could originate from CD or both PT and LOH, suggesting heterogeneity of polycystic composition and origin. Furthermore, cyst epithelial cells with different origins have different gene set activation.

Aquaporins in insulin resistance and diabetes: More than channels!

Aquaporins (AQPs) are part of the family of the integral membrane proteins. Their function is dedicated to the transport of water, glycerol, ammonia, urea, H2O2, and other small molecules across the biological membranes. Although for many years they were scarcely considered, AQPs have a relevant role in the development of many diseases. Recent discoveries suggest, that AQPs may play an important role in the process of fat accumulation and regulation of oxidative stress, two crucial aspects of insulin resistance and type-2 diabetes (T2D). Insulin resistance (IR) and T2D are multi-faceted systemic diseases with multiple connections to obesity and other comorbidities such as hypertension, dyslipidemia and metabolic syndrome. Both IR and T2D transcends different tissues and organs, creating the maze of mutual relationships between adipose fat depots, skeletal muscle, liver and other insulin-sensitive organs. AQPs with their heterogenous properties, distinctive tissue distribution and documented involvement in both the lipid metabolism and regulation of the oxidative stress appear to be feasible candidates in the search for the explanation to this third-millennium plague. A lot of research has been assigned to adipose tissue AQP7 and liver tissue AQP9, clarifying their relationship and coordinated work in the induction of hepatic insulin resistance. Novel research points also to other aquaporins, such as AQP11 which may be associated with the induction of insulin resistance and T2D through its involvement in hydrogen peroxide transport. In this review we collected recent discoveries in the field of AQP's involvement in the insulin resistance and T2D. Novel paths which connect AQPs with metabolic disorders can give new fuel to the research on obesity, insulin resistance and T2D - one of the most worrying problems of the modern society.

A Multitubular Kidney-on-Chip to Decipher Pathophysiological Mechanisms in Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major renal pathology provoked by the deletion of PKD1 or PKD2 genes leading to local renal tubule dilation followed by the formation of numerous cysts, ending up with renal failure in adulthood. In vivo, renal tubules are tightly packed, so that dilating tubules and expanding cysts may have mechanical influence on adjacent tubules. To decipher the role of this coupling between adjacent tubules, we developed a kidney-on-chip reproducing parallel networks of tightly packed tubes. This original microdevice is composed of cylindrical hollow tubes of physiological dimensions, parallel and closely packed with 100-200 μm spacing, embedded in a collagen I matrix. These multitubular systems were properly colonized by different types of renal cells with long-term survival, up to 2 months. While no significant tube dilation over time was observed with Madin-Darby Canine Kidney (MDCK) cells, wild-type mouse proximal tubule (PCT) cells, or with PCT Pkd1 +/- cells (with only one functional Pkd1 allele), we observed a typical 1.5-fold increase in tube diameter with isogenic PCT Pkd1 -/- cells, an ADPKD cellular model. This tube dilation was associated with an increased cell proliferation, as well as a decrease in F-actin stress fibers density along the tube axis. With this kidney-on-chip model, we also observed that for larger tube spacing, PCT Pkd1 -/- tube deformations were not spatially correlated with adjacent tubes whereas for shorter spacing, tube deformations were increased between adjacent tubes. Our device reveals the interplay between tightly packed renal tubes, constituting a pioneering tool well-adapted to further study kidney pathophysiology.

Genomic and expression characterization of aquaporin genes from Siniperca chuatsi

Aquaporins (AQPs) are major intrinsic proteins that form pores in the membranes of biological cells. We first cloned the full-length sequences of aqp0, 1, 3, 4, 7, 8, 9, 10, 11, and 12 genes in Siniperca chuatsi. The 10 S. chuatsi aqp (Sc-aqp) genes included complete open reading frames and exhibited different exon-intron organizations. Sc-aqp1, 3, 8, 9, 10, and 11 were mostly expressed in the gallbladder, gills, gastric cecum, liver, ovaries, and spleen, respectively; Sc-aqp0 and 4 were mostly expressed in larvae at 1 day after hatching and in gastrula; Sc-aqp7 and 12 were mostly expressed in 2K-cell embryos. The expression levels of Sc-aqp1, 3, 7, 8, 9, and 10 after 10 part per thousand (ppt) salt treatment had significantly changed compared with those after 0 ppt salt treatment. Real-time quantitative PCR analysis further showed that in the intestines, the mRNA levels of Sc-aqp1 and 10 significantly decreased by approximately 2.07- and 2.85-fold, respectively, whereas those of Sc-aqp8 and 9 significantly increased by approximately 7.08- and 4.14-fold, respectively. Sc-aqp1, 8, 9, and 10 showed no significant differences in the gills. Sc-aqp3 significantly decreased by approximately 1.51- and 1.67-fold in the gills and intestines, respectively. Sc-aqp7 significantly increased by approximately 4.18- and 7.04-fold in the gills and intestines, respectively. This study was the first to investigate the tissue expression profiles and response to salt stress of aqp genes in S. chuatsi. Moreover, altering diet and suffering from immune stress could cause changes in the expression level of aqps. This study provided valuable reference information for AQPs' roles in osmoregulation in freshwater fish.

Association of Serum PSP/REG Iα with Renal Function in Type 2 Diabetes Mellitus

PURPOSE

Pancreatic stone protein/regenerating protein I (PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG I.

METHODS

This cross-sectional study was conducted at Zhongda Hospital, affiliated with Southeast University in China. Serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG I.

RESULTS

Serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG IP < 0.05). The level of PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG I.

CONCLUSIONS

Serum PSP/REG Iα level is significantly upregulated in T2DM patients and reflects renal function in both T2DM and nondiabetic control groups. The relationship between PSP/REG Iα and eGFR suggested that PSP/REG Iα might be a potential indicator of renal dysfunction.α) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG Iα) is a secretory protein mainly detected in the pancreas. Recent studies revealed increased serum PSP/REG I.

Aquaporins in the kidney: physiology and pathophysiology

The kidney is the central organ involved in maintaining water and sodium balance. In human kidneys, nine aquaporins (AQPs), including AQP1-8 and AQP11, have been found and are differentially expressed along the renal tubules and collecting ducts with distinct and critical roles in the regulation of body water homeostasis and urine concentration. Dysfunction and dysregulation of these AQPs result in various water balance disorders. This review summarizes current understanding of physiological and pathophysiological roles of AQPs in the kidney, with a focus on recent progress on AQP2 regulation by the nuclear receptor transcriptional factors. This review also provides an overview of AQPs as clinical biomarkers and therapeutic targets for renal diseases.

Association of Serum PSP/REG Iα with Renal Function in Pregnant Women

Pancreatic stone protein/regenerating protein Iα (PSP/REG Iα) is a secretory protein produced in the pancreas, but its expression has also been observed in the kidney. It may be associated with kidney dysfunction. This study investigates the possible association between PSP/REG Iα and kidney function in pregnant women. Serum PSP/REG Iα levels were measured by a specific ELISA enzyme-linked immunosorbent assay. Maternal information and clinical and biochemical parameters were collected. Estimated glomerular filtration rate (eGFR) was calculated for all individuals to evaluate their renal function. Spearman's correlation and multiple linear regression analyses were performed to assess the associations between PSP/REG Iα and eGFR, serum creatinine (Cr), blood urea nitrogen (BUN), and uric acid (UA). A total of 595 pregnant women were enrolled in the study. Participants with mildly reduced eGFR had higher PSP/REG Iα levels [50.49 (35.02, 58.64)] than in the general population [26.84 (21.02, 33.07)] (p < 0.001). Included participants were stratified into PSP/REG Iα quartiles; significant differences were observed in the levels of eGFR, serum Cr, BUN, and UA. PSP/REG Iα was negatively correlated with eGFR (r = −0.402, p < 0.001) and positively associated with serum Cr (r = 0.468, p < 0.001), BUN (r = 0.166, p < 0.001), and UA (r = 0.207, p < 0.001). The linear regression analysis indicated that PSP/REG Iα was associated with UA, BUN, and eGFR. High PSP/REG Iα concentrations were closely associated with renal dysfunction in pregnant women. Our study provides clinical evidence that serum PSP/REG Iα levels could be a novel biomarker for assessment of renal function in pregnant women.

Aquaporins in Renal Diseases

Aquaporins (AQPs) are a family of highly selective transmembrane channels that mainly transport water across the cell and some facilitate low-molecular-weight solutes. Eight AQPs, including AQP1, AQP2, AQP3, AQP4, AQP5, AQP6, AQP7, and AQP11, are expressed in different segments and various cells in the kidney to maintain normal urine concentration function. AQP2 is critical in regulating urine concentrating ability. The expression and function of AQP2 are regulated by a series of transcriptional factors and post-transcriptional phosphorylation, ubiquitination, and glycosylation. Mutation or functional deficiency of AQP2 leads to severe nephrogenic diabetes insipidus. Studies with animal models show AQPs are related to acute kidney injury and various chronic kidney diseases, such as diabetic nephropathy, polycystic kidney disease, and renal cell carcinoma. Experimental data suggest ideal prospects for AQPs as biomarkers and therapeutic targets in clinic. This review article mainly focuses on recent advances in studying AQPs in renal diseases.

Involvement of the NADPH oxidase 2 pathway in renal oxidative stress in Aqp11 -/- mice

Aquaporin-11 (AQP11) is an intracellular AQP. Several studies with Aqp11^-/- mice have shown that AQP11 has a role in normal development of the kidney after birth. Our previous studies have suggested that alteration of oxygen homeostasis may be involved in the kidney injury caused by AQP11 deficiency, although the underlying mechanism is largely unknown. To clarify this issue, we examined genes that are related to oxygen homeostasis in Aqp11^-/- mice. Among 62 genes that are involved in oxygen homeostasis, 35 were upregulated by more than 2-fold in Aqp11^-/- mice in comparison with wild-type mice. Pathway analysis using these genes extracted the pathway responsible for production of reactive oxygen species in macrophages. As expression of the genes involved in the NADPH oxidase 2 (NOX2) complex was dramatically increased by more than 14-fold, we further analyzed NOX2 at the protein level. Immunoblotting analysis demonstrated a dramatic increase of NOX2 protein in the kidney of Aqp11^-/- mice, and immunohistochemistry showed that NOX2 protein and a marker protein for macrophages were increased in the renal interstitium. These results indicate that NOX2-induced oxidative stress accompanied by macrophage infiltration plays an important role in alteration of oxygen homeostasis in Aqp11^-/- mice.

•

In Aqp11^-/- mice, renal oxidative stress has been shown to occur, but the molecular pathway involved is largely unknown.

•

mRNA levels of 35 genes related to oxidative stress and hypoxia are upregulated.

•

Among them, the NADPH oxidase 2 pathway was found to be dramatically activated in the kidney of Aqp11^-/- mice.

•

Activation of this pathway is considered to play an important role in increased renal oxidative stress in Aqp11^-/- mice.

Arginine reprogramming in ADPKD results in arginine-dependent cystogenesis

Research into metabolic reprogramming in cancer has become commonplace, yet this area of research has only recently come of age in nephrology. In light of the parallels between cancer and autosomal dominant polycystic kidney disease (ADPKD), the latter is currently being studied as a metabolic disease. In clear cell renal cell carcinoma (RCC), which is now considered a metabolic disease, we and others have shown derangements in the enzyme arginosuccinate synthase 1 (ASS1), resulting in RCC cells becoming auxotrophic for arginine and leading to a new therapeutic paradigm involving reducing extracellular arginine. Based on our earlier finding that glutamine pathways are reprogrammed in ARPKD, and given the connection between arginine and glutamine synthetic pathways via citrulline, we investigated the possibility of arginine reprogramming in ADPKD. We now show that, in a remarkable parallel to RCC, ASS1 expression is reduced in murine and human ADPKD, and arginine depletion results in a dose-dependent compensatory increase in ASS1 levels as well as decreased cystogenesis in vitro and ex vivo with minimal toxicity to normal cells. Nontargeted metabolomics analysis of mouse kidney cell lines grown in arginine-deficient versus arginine-replete media suggests arginine-dependent alterations in the glutamine and proline pathways. Thus, depletion of this conditionally essential amino acid by dietary or pharmacological means, such as with arginine-degrading enzymes, may be a novel treatment for this disease.

Prognostic values of aquaporins mRNA expression in human ovarian cancer

Aquaporins (AQPs), a family of transmembrane channel, are composed of 13 identified members (AQP0–12). Accumulating evidences reported that AQPs were correlated with various biological roles and represented a prognostic predictor in various cancer types. However, the prognostic value of AQPs expression in ovarian cancer remains unclear. Using ‘Kaplan–Meier plotter’ (KM plotter) online database, we explored the predictive prognostic value of individual AQPs members’ mRNA expression to overall survival (OS) in different clinical data, such as histology, pathological grades, clinical stages, TP53 status, and applied chemotherapy in ovarian cancer patients. Our results revealed that higher AQP0, AQP1, and AQP4 mRNA expression were correlated with poor OS, whereas higher AQP3, AQP5, AQP6, AQP8, AQP10, and AQP11 showed better OS in ovarian cancer patients. Moreover, AQP4 and AQP8 showed poor OS in TP53-mutated ovarian cancer patients and AQP1 presented unfavorable OS in both TP53 mutated and wild ovarian cancer patients. Additionally, AQP3, AQP6, and AQP11 mRNA expression were correlated with better OS, whereas AQP0 and AQP1 showed poor OS in all ovarian cancer patients treated with Platin, Taxol, and Taxol + Platin chemotherapy. AQP5, AQP8, and AQP10 were associated with improved OS, however, AQP4 predicted unfavorable OS in all patients treated with Platin chemotherapy. Our results suggest that individual AQPs, except AQP2 and AQP9, are associated with unique prognostic significance and may thus act as new predictive prognostic indicators and potential drug therapeutic target in ovarian cancer.