PGE2 receptor EP3 inhibits water reabsorption and contributes to polyuria and kidney injury in a streptozotocin-induced mouse model of diabetes

Deletion of the prostaglandin EP4 receptor in the kidney tubule of mature mice alters kidney water handling only in males

Prostaglandin E2 (PGE2) is a lipid mediator modulating several aspects of kidney function. PGE2 acts via four prostanoid receptors, EP1 to EP4. In renal tubules, EP4 has very low expression, yet a role for EP4 in maintaining water balance has been proposed. The major aim of this study was to clarify the role of the EP4 receptor in the kidney tubule of adult mice for body water homeostasis. To examine this, a mouse model with doxycycline-dependent deletion of EP4 along the renal tubule (Pax8Cre system) was developed and phenotyped with respect to water handling. Two weeks after doxycycline treatment, EP4 mRNA expression (RT-qPCR) was reduced by >80% in the medulla of male and female knockout mice (EP4-/-) compared with controls (EP4+/+). With free access to water, there were no detectable differences between genotypes in food intake, body weight, or plasma biochemistries. Male, but not female, EP4-/- mice had a small but significantly higher basal urinary output with decreased osmolality, concomitant with lower urinary Na+, K+, Cl-, urea, and creatinine concentrations. The urea channel UT-A1 was reduced in the medulla, but otherwise no major differences in the levels of proteins involved in water balance were observed between genotypes. There were no differences between genotypes in their ability to concentrate urine during a 14-h water restriction or after treatment with the vasopressin V2 receptor agonist 1-deamino-8-d-arginine-vasopressin. EP4-/- mice of both sexes excreted an acute water load similarly to control mice. In conclusion, EP4 in the renal tubule has a mild role in renal water handling, but only in male mice. This new model provides a novel tool for assessing the role of EP4 in kidney tubule function in various (patho)physiological conditions independently of developmental abnormalities or systemic effects.NEW & NOTEWORTHY Acting through the EP1-EP4 receptors, prostaglandin E2 (PGE2) modulates various aspects of kidney function. Despite extremely low expression in the collecting duct, EP4 has been proposed to play a key role in regulation of Aquaporin-2 and water balance. In this study, we show that EP4 only plays a mild role in kidney water handling in male mice, calling into question the standard concepts presented in physiology textbooks regarding PGE2 actions on the collecting duct.

Tea drinking effectively improves symptoms of diabetes and prevents hepatorenal damage in mice

Since type 2 diabetic patients often develop resistance to metformin as the progresses of diabetes, and almost all type 1 diabetic patients need receive insulin injection for hyperglycemia control. It is important to explore novel strategies with different mechanisms for diabetes management. Glucose-induced osmotic diuresis, known as polyuria, is the first clinical symptom in severe type 2 diabetes mellitus (T2DM) and type 1 diabetes mellitus (T1DM). Drinking green tea or black tea effectively mitigates diabetic symptoms including polyuria, polydipsia, polyphagia and hyperglycemia in db/db mice via regulating renal aquaporin 2 and urine transporter A1 (UT-A1), in favor renal water reabsorption. This unique mechanism of action of tea could be useful for the treatment of diabetes in humans. In this study, we found that drinking Large-leaf yellow tea (LYT) for 5 weeks effectively ameliorated polyuria, polydipsia, polyphagia, hyperglycemia and excessive body weight gain, as well as upregulated renal water reabsorption associated proteins, including protein kinase C-alpha (PKC-α), membrane PKC-α and glycosylated UT-A1 in db/db mice. Four-days experiment were also confirmed the rapidly response of these proteins in favor renal water reabsorption and the amelioration of diabetic symptoms by LYT. We also found that green tea drinking effectively mitigated symptoms of diabetes in a mouse model for T1DM via upregulating these proteins. Moreover, green tea drinking prevented hepatorenal damage caused by hyperglycemia as suggested by the reduced levels of aspartate aminotransferase and creatinine in serum and the enhanced antioxidant defense system in liver and kidney. These results suggest the possible application of tea or tea constitutes in the clinical treatment of severe T2DM and T1DM, and the kidney is the target organ.

Inducible deletion of the prostaglandin EP3 receptor in kidney tubules of male and female mice has no major effect on water homeostasis

The prostaglandin E2 (PGE2) receptor EP3 has been detected in the thick ascending limb (TAL) and the collecting duct of the kidney, where its actions are proposed to inhibit water reabsorption. However, EP3 is also expressed in other cell types, including vascular endothelial cells. The aim here was to determine the contribution of EP3 in renal water handling in male and female adult mice by phenotyping a novel mouse model with doxycycline-dependent deletion of EP3 throughout the kidney tubule (EP3-/- mice). RNAscope demonstrated that EP3 was highly expressed in the cortical and medullary TAL of adult mice. Compared with controls EP3 mRNA expression was reduced by >80% in whole kidney (RT-qPCR) and nondetectable (RNAscope) in renal tubules of EP3-/- mice. Under basal conditions, there were no significant differences in control and EP3-/- mice of both sexes in food and water intake, body weight, urinary output, or clinical biochemistries. No differences were detectable between genotypes in handling of an acute water load or in their response to the vasopressin analog 1-deamino-8-d-arginine-vasopressin (dDAVP). No differences in water handling were observed when PGE2 production was enhanced using 1% NaCl load. Expression of proteins involved in kidney water handling was not different between genotypes. This study demonstrates that renal tubular EP3 is not essential for body fluid homeostasis in males or females, even when PGE2 levels are high. The mouse model is a novel tool for examining the role of EP3 in kidney function independently of potential developmental abnormalities or systemic effects.NEW & NOTEWORTHY The prostanoid EP3 receptor is proposed to play a key role in the kidney tubule and antagonize the effects of vasopressin on aquaporin-mediated water reabsorption. Here, we phenotyped a kidney tubule-specific inducible knockout mouse model of the EP3 receptor. Our major finding is that, even under physiological stress, tubular EP3 plays no detectable role in renal water or solute handling. This suggests that other EP receptors must be important for renal salt and water handling.

The Influence of Soy Isoflavones and Soy Isoflavones with Inulin on Kidney Morphology, Fatty Acids, and Associated Parameters in Rats with and without Induced Diabetes Type 2

Diabetes mellitus resulting from hyperglycemia stands as the primary cause of diabetic kidney disease. Emerging evidence suggests that plasma concentrations of soy isoflavones, substances with well-established antidiabetic properties, rise following supplemental inulin administration. The investigation encompassed 36 male Sprague-Dawley (SD) rats segregated into two cohorts: non-diabetic and diabetic, induced with type 2 diabetes (high-fat diet + two intraperitoneal streptozotocin injections). Each cohort was further divided into three subgroups (n = 6): control, isoflavone-treated, and isoflavone plus inulin-treated rats. Tail blood glucose and ketone levels were gauged. Upon termination, blood samples were drawn directly from the heart for urea, creatinine, and HbA1c/HbF analyses. One kidney per rat underwent histological (H-E) and immunohistochemical assessments (anti-AQP1, anti-AQP2, anti-AVPR2, anti-SLC22A2, anti-ACC-alpha, anti-SREBP-1). The remaining kidney underwent fatty acid methyl ester analysis. Results unveiled notable alterations in water intake, body and kidney mass, kidney morphology, fatty acids, AQP2, AVPR2, AcetylCoA, SREBP-1, blood urea, creatinine, and glucose levels in control rats with induced type 2 diabetes. Isoflavone supplementation exhibited favorable effects on plasma urea, plasma urea/creatinine ratio, glycemia, water intake, and kidney mass, morphology, and function in type 2 diabetic rats. Additional inulin supplementation frequently modulated the action of soy isoflavones.

Revisiting prostaglandin E2: A promising therapeutic target for osteoarthritis

Osteoarthritis (OA) is a complex disease characterized by cartilage degeneration and persistent pain. Prostaglandin E2 (PGE2) plays a significant role in OA inflammation and pain. Recent studies have revealed the significant role of PGE2-mediated skeletal interoception in the progression of OA, providing new insights into the pathogenesis and treatment of OA. This aspect also deserves special attention in this review. Additionally, PGE2 is directly involved in pathologic processes including aberrant subchondral bone remodeling, cartilage degeneration, and synovial inflammation. Therefore, celecoxib, a commonly used drug to alleviate inflammatory pain through inhibiting PGE2, serves not only as an analgesic for OA but also as a potential disease-modifying drug. This review provides a comprehensive overview of the discovery history, synthesis and release pathways, and common physiological roles of PGE2. We discuss the roles of PGE2 and celecoxib in OA and pain from skeletal interoception and multiple perspectives. The purpose of this review is to highlight PGE2-mediated skeletal interoception and refresh our understanding of celecoxib in the pathogenesis and treatment of OA.

Single-cell and transcriptome analysis reveals TAL cells in diabetic nephropathy

Diabetic nephropathy is a global public health concern with multifaceted pathogenesis, primarily involving hypertension. Excessive activation of AT1R has been strongly associated with hypertension onset and progression in diabetic nephropathy. This study aimed to conduct thick ascending limb cell single-cell and transcriptomic analysis in diabetic nephropathy, including screening for biological markers, cellular communication, and immune infiltration, to identify potential biomarkers and effective means for prevention and treatment. By using high-dimensional weighted gene co-expression network analysis, least absolute shrinkage and selection operator, machine learning, neural deconvolution, quasi-chronological analysis, non-negative matrix factorization clustering, and monocyte chemotactic protein-induced counter, we identified 7 potential thick ascending limb cell biomarkers for diabetic nephropathy and elucidated the bone morphogenetic protein pathway's regulation of thick ascending limb cells through podocyte epithelial cells and podocyte cells. The study also highlighted the role of COBL, PPARGC1A, and THSD7A in non-negative matrix factorization clustering and their relationship with thick ascending limb cell immunity in diabetic nephropathy. Our findings provide new insights and avenues for managing diabetic nephropathy, ultimately alleviating the burden on patients and society.

What the BTBR/J mouse has taught us about diabetes and diabetic complications

Human and mouse genetics have delivered numerous diabetogenic loci, but it is mainly through the use of animal models that the pathophysiological basis for their contribution to diabetes has been investigated. More than 20 years ago, we serendipidously identified a mouse strain that could serve as a model of obesity-prone type 2 diabetes, the BTBR (Black and Tan Brachyury) mouse (BTBR T+ Itpr3tf/J, 2018) carrying the Lepob mutation. We went on to discover that the BTBR-Lepob mouse is an excellent model of diabetic nephropathy and is now widely used by nephrologists in academia and the pharmaceutical industry. In this review, we describe the motivation for developing this animal model, the many genes identified and the insights about diabetes and diabetes complications derived from >100 studies conducted in this remarkable animal model.

Amelioration of exosome and mesenchymal stem cells in rats infected with diabetic nephropathy by attenuating early markers and aquaporin-1 expression

Diabetic nephropathy (DN) is a prevalent diabetic microvascular condition. It is the leading cause of kidney disease in the advanced stages. There is no currently effective treatment available. This research aimed to investigate the curative potentials of exosomes isolated from mesenchymal stem cells affecting DN. This study was performed on 70 male adult albino rats. Adult rats were randomized into seven groups: Group I: Negative control group, Group II: DN group, Group III: Balanites treated group, Group IV: MSCs treated group, Group V: Exosome treated group, Group VI: Balanites + MSCs treated group and Group VII: Balanites + exosome treated group. Following the trial period, blood and renal tissues were subjected to biochemical, gene expression analyses, and histopathological examinations. Results showed that MDA was substantially increased, whereas TAC was significantly decreased in the kidney in the DN group compared to normal health rats. Undesired elevated values of MDA levels and a decrease in TAC were substantially ameliorated in groups co-administered Balanites aegyptiacae with MSCs or exosomes compared to the DN group. A substantial elevation in TNF-α and substantially diminished concentration of IGF-1 were noticed in DN rats compared to normal health rats. Compared to the DN group, the co-administration of Balanites aegyptiacae with MSCs or exosomes substantially improved the undesirable elevated values of TNF-α and IGF-1. Furthermore, in the DN group, the mRNA expression of Vanin-1, Nephrin, and collagen IV was significantly higher than in normal healthy rats. Compared with DN rats, Vanin-1, Nephrin, and collagen IV Upregulation were substantially reduced in groups co-administered Balanites aegyptiacae with MSCs or exosomes. In DN rats, AQP1 expression was significantly lower than in normal healthy rats. Furthermore, the groups co-administered Balanites aegyptiacae with MSCs or exosomes demonstrated a substantial increase in AQP1 mRNA expression compared to DN rats.

Benzo[a]pyrene Exposure Reduces Cell-Type Diversity and Stimulates Sex-Biased Damage Pathways in End Organs of Lupus-Prone Mice

Studies indicate that genetic factors only account for approximately thirty percent of all autoimmune diseases, while the rest of autoimmune pathogenesis is attributed to environmental factors including toxic chemicals. To understand if and how environmental pollutants trigger autoimmunity, we investigated the effect of benzo[a]pyrene (BaP) exposure on the development of autoimmune phenotypes in the lupus-prone MRL strain. The exposure of MRL mice to BaP over the course of 8 weeks before lupus onset resulted in total body weight loss in males, while marginal changes in anti-dsDNA levels occurred. Multi-organ analyses of BaP-treated and control MRL mice suggested that the kidney is a major organ directly affected by the metabolism of benzene-containing compounds, with increased expression of BaP-target genes including Cyp4b1 and Hao2. Intriguingly, spatial transcriptomic data showed that BaP caused a drastic reduction in cell-type diversity in both the kidneys and spleen of MRL mice. Further analysis of the molecular pathways affected suggested a sex-biased effect of BaP treatment, with the upregulated expression of angiogenesis genes in the lungs and an increased deposition of C3 in the kidneys of male mice. While SLE is more common in women, the disease is more severe in male patients, with an increased risk of disease progression to renal failure and lung cancer. Our results reveal sex-biased molecular pathways stimulated by BaP which may help explain the increased likelihood of end organ damage in males with lupus.

The Link between Prostanoids and Cardiovascular Diseases

Cardiovascular diseases are the leading cause of global deaths, and many risk factors contribute to their pathogenesis. In this context, prostanoids, which derive from arachidonic acid, have attracted attention for their involvement in cardiovascular homeostasis and inflammatory processes. Prostanoids are the target of several drugs, but it has been shown that some of them increase the risk of thrombosis. Overall, many studies have shown that prostanoids are tightly associated with cardiovascular diseases and that several polymorphisms in genes involved in their synthesis and function increase the risk of developing these pathologies. In this review, we focus on molecular mechanisms linking prostanoids to cardiovascular diseases and we provide an overview of genetic polymorphisms that increase the risk for cardiovascular disease.

Comparative analysis of hypertensive nephrosclerosis in animal models of hypertension and its relevance to human pathology. Glomerulopathy

Current research on hypertension utilizes more than fifty animal models that rely mainly on stable increases in systolic blood pressure. In experimental hypertension, grading or scoring of glomerulopathy in the majority of studies is based on a wide range of opinion-based histological changes that do not necessarily comply with lesional descriptors for glomerular injury that are well-established in clinical pathology. Here, we provide a critical appraisal of experimental hypertensive glomerulopathy with the same approach used to assess hypertensive glomerulopathy in humans. Four hypertensive models with varying pathogenesis were analyzed–chronic angiotensin II infused mice, mice expressing active human renin in the liver (TTRhRen), spontaneously hypertensive rats (SHR), and Goldblatt two-kidney one-clip rats (2K1C). Analysis of glomerulopathy utilized the same criteria applied in humans–hyalinosis, focal segmental glomerulosclerosis (FSGS), ischemic, hypertrophic and solidified glomeruli, or global glomerulosclerosis (GGS). Data from animal models were compared to human reference values. Kidneys in TTRhRen mice, SHR and the nonclipped kidneys in 2K1C rats had no sign of hyalinosis, FSGS or GGS. Glomerulopathy in these groups was limited to variations in mesangial and capillary compartment volumes, with mild increases in collagen deposition. Histopathology in angiotensin II infused mice corresponded to mesangioproliferative glomerulonephritis, but not hypertensive glomerulosclerosis. The number of nephrons was significantly reduced in TTRhRen mice and SHR, but did not correlate with severity of glomerulopathy. The most substantial human-like glomerulosclerotic lesions, including FSGS, ischemic obsolescent glomeruli and GGS, were found in the clipped kidneys of 2K1C rats. The comparison of affected kidneys to healthy control in animals produces lesion values that are numerically impressive but correspond to mild damage if compared to humans. Animal studies should be standardized by employing the criteria and classifications established in human pathology to make experimental and human data fully comparable for comprehensive analysis and model improvements.

Roles of EP Receptors in the Regulation of Fluid Balance and Blood Pressure

Prostaglandin E2 (PGE2) is an important prostanoid expressing throughout the kidney and cardiovascular system. Despite the diverse effects on fluid metabolism and blood pressure, PGE2 is implicated in sustaining volume and hemodynamics homeostasis. PGE2 works through four distinct E-prostanoid (EP) receptors which are G protein-coupled receptors. To date, pharmacological specific antagonists and agonists of all four subtypes of EP receptors and genetic targeting knockout mice for each subtype have helped in uncoupling the diverse functions of PGE2 and discriminating the respective characteristics of each receptor. In this review, we summarized the functions of individual EP receptor subtypes in the renal and blood vessels and the molecular mechanism of PGE2-induced fluid metabolism and blood pressure homeostasis.

Prostaglandin EP3 receptor signaling is required to prevent insulin hypersecretion and metabolic dysfunction in a non-obese mouse model of insulin resistance

When homozygous for the Leptin^Ob mutation (Ob), Black-and-Tan Brachyury (BTBR) mice become morbidly obese and severely insulin resistant, and by 10 wk of age, frankly diabetic. Previous work has shown prostaglandin EP3 receptor (EP3) expression and activity is upregulated in islets from BTBR-Ob mice as compared with lean controls, actively contributing to their β-cell dysfunction. In this work, we aimed to test the impact of β-cell-specific EP3 loss on the BTBR-Ob phenotype by crossing Ptger3 floxed mice with the rat insulin promoter (RIP)-Cre^Herr driver strain. Instead, germline recombination of the floxed allele in the founder mouse-an event whose prevalence we identified as directly associated with underlying insulin resistance of the background strain-generated a full-body knockout. Full-body EP3 loss provided no diabetes protection to BTBR-Ob mice but, unexpectedly, significantly worsened BTBR-lean insulin resistance and glucose tolerance. This in vivo phenotype was not associated with changes in β-cell fractional area or markers of β-cell replication ex vivo. Instead, EP3-null BTBR-lean islets had essentially uncontrolled insulin hypersecretion. The selective upregulation of constitutively active EP3 splice variants in islets from young, lean BTBR mice as compared with C57BL/6J, where no phenotype of EP3 loss has been observed, provides a potential explanation for the hypersecretion phenotype. In support of this, high islet EP3 expression in Balb/c females versus Balb/c males was fully consistent with their sexually dimorphic metabolic phenotype after loss of EP3-coupled Gα_z protein. Taken together, our findings provide a new dimension to the understanding of EP3 as a critical brake on insulin secretion.NEW & NOTEWORTHY Islet prostaglandin EP3 receptor (EP3) signaling is well known as upregulated in the pathophysiological conditions of type 2 diabetes, contributing to β-cell dysfunction. Unexpected findings in mouse models of non-obese insulin sensitivity and resistance provide a new dimension to our understanding of EP3 as a key modulator of insulin secretion. A previously unknown relationship between mouse insulin resistance and the penetrance of rat insulin promoter-driven germline floxed allele recombination is critical to consider when creating β-cell-specific knockouts.

Endothelium-dependent contraction: The non-classical action of endothelial prostacyclin, its underlying mechanisms, and implications

Although commonly thought to produce prostacyclin (prostaglandin I₂ ; PGI₂ ) that evokes vasodilatation and protects vessels from the development of diseases, the endothelial cyclooxygenase (COX)-mediated metabolism has also been found to release substance(s) called endothelium-derived contracting factor(s) (EDCF) that causes endothelium-dependent contraction and implicates in endothelial dysfunction of disease conditions. Various mechanisms have been proposed for the process; however, the major endothelial COX metabolite PGI₂ , which has been classically considered to activate the I prostanoid receptor (IP) that mediates vasodilatation and opposes the effects of thromboxane (Tx) A₂ produced by COX in platelets, emerges as a major EDCF in health and disease conditions. Our recent studies from genetically altered mice further suggest that vasomotor reactions to PGI₂ are collectively modulated by IP, the vasoconstrictor Tx-prostanoid receptor (TP; the prototype receptor of TxA₂ ) and E prostanoid receptor-3 (EP3; a vasoconstrictor receptor of PGE₂ ) although with differences in potency and efficacy; a contraction to PGI₂ reflects activities of TP and/or EP3 outweighing that of the concurrently activated IP. Here, we discuss the history of endothelium-dependent contraction, evidences that support the above hypothesis, proposed mechanisms for the varied reactions to endothelial PGI₂ synthesis as well as the relation of its dilator activity to the effect of another NO-independent vasodilator mechanism, the endothelium-derived hyperpolarizing factor. Also, we address the possible pathological and therapeutic implications as well as questions remaining to be resolved or limitations of our above findings obtained from genetically altered mouse models.

PTGER3 and MMP-2 play potential roles in diabetic nephropathy via competing endogenous RNA mechanisms

BACKGROUND

Diabetic nephropathy (DN) is a primary complication of diabetes mellitus (DM). The pathology of DN is still vague, and diagnostic accuracy is not enough. This study was performed to identify miRNAs and genes that have possibilities of being used as therapeutic targets for DN in type 2 DM.

METHODS

Human miRNA data GSE51674 and gene data GSE111154 were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) and miRNAs (DEmiRNAs) in the kidney between control and DN patients were screened out. The competing endogenous RNA (ceRNA) network was constructed, and key lncRNA-miRNA-mRNA pairs were selected accordingly. Potential drugs targeting DEGs were screened out and validated using PCR analysis.

RESULTS

Totally, 83 DEmiRNAs and 293 DEGs were identified in GSE51674 and GSE111154, respectively. Thirteen of the top 20 DEmiRNAs (10 up and 10 down) targeted to 47 DEGs. In the ceRNA network, RP11-363E7.4/TTN-AS1/HOTAIRM1-hsa-miR-106b-5p-PTGER3 and LINC00960-hsa-miR-1237-3p-MMP-2 interaction pairs were identified as the key ceRNA network. Interestingly, PTGER3 and hsa-miR-1237-3p were downregulated, and MMP-2 and hsa-miR-106b-5p were upregulated in the kidney of patients with DN compared with normal controls, respectively. PTGER3 and MMP-2 were targeted by drugs including iloprost, treprostinil, or captopril, and the deregulation of the two genes was confirmed in the plasma samples from patients with DN as compared with controls.

CONCLUSIONS

We speculated that the RP11-363E7.4/TTN-AS1/HOTAIRM1-hsa-miR-106b-5p-PTGER3 and LINC00960-hsa-miR-1237-3p-MMP-2 networks were associated with diabetic renal injury.

Tea Drinking Alleviates Diabetic Symptoms via Upregulating Renal Water Reabsorption Proteins and Downregulating Renal Gluconeogenic Enzymes in db/db Mice

SCOPE

Tea, made from the plant Camellia sinensis, is known to have anti-diabetes effects and different mechanisms of action are proposed. Kidney is a vital organ in managing water reabsorption and glucose metabolism, and is greatly influenced by diabetes. The present study investigates the effects of tea administration on water reabsorption and gluconeogenesis in the kidney of diabetic mice.

METHODS AND RESULTS

Db/db mice are given tea infusion as drinking fluid when they begin to exhibit hyperglycemia. It is found that green tea or black tea infusion potently elevates renal proteins vital for water reabsorption, including protein kinase C-α, aquaporin 2, and urea transporter-A1, as well as increases trafficking of these proteins to apical plasma membrane where they exert water reabsorption function. The treatment also downregulates renal gluconeogenic enzymes, including glucose-6-phosphatase-α and phosphoenolpyruvate carboxykinase. Associated with these biochemical changes are the rectified polyuria, polydipsia, polyphagia, and hyperglycemia, all symptoms of diabetes.

CONCLUSIONS

For the first time, the present study demonstrates that tea has robust effects in enhancing kidney water reabsorption proteins and downregulating gluconeogenic enzymes in db/db mice. It remains to be investigated whether such beneficial effects of tea occur in humans.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Effects of thromboxane prostanoid receptor deficiency on diabetic nephropathy induced by high fat diet and streptozotocin in mice

Diabetic nephropathy (DN), one of the main causes of end-stage renal disease, still remains as a challenge of clinical management. This study aimed to determine whether deficiency of the thromboxane (TX) prostanoid receptor (TP), which mediates the contractile activities of all prostanoids, alleviates the development of DN and if so, to examine the underlying mechanism(s). Diabetes was induced by high fat diet and streptozotocin injection in wild-type (WT) mice and those with TP deficiency (TP^-/-). Here we show that WT and TP^-/- mice developed diabetes with a similar blood glucose level; however, signs of renal functional impairments and pathologies occurred to a lesser extent in TP^-/- than in WT mice. Also, the extent of an increase in the expression level of transforming growth factor-β1 (TGF-β1), a common pathological mediator of DN, in diabetic renal cortexes of TP^-/- mice was lower than that of WT counterparts. Moreover, we noted that expression levels of cyclooxygenase (COX)-2 and calcium-dependent phospholipase A₂ (cPLA₂) as well as levels of prostaglandin E₂ and TXA₂ in diabetic renal cortexes were increased as compared to those of non-diabetic conditions. These results thus demonstrate that possibly due to up-regulated cPLA₂ and COX-2 that lead to increased prostanoid syntheses in diabetic renal cortexes, TP^-/- alleviates DN development. In addition, our results suggest that such an effect of TP^-/- might be related to the suppression of TGF-β1 up-regulation that is commonly associated with the disease condition.

Prostaglandin E2 receptor EP1 (PGE2/EP1) deletion promotes glomerular podocyte and endothelial cell injury in hypertensive TTRhRen mice

Prostaglandin E2 receptor EP1 (PGE₂/EP₁) promotes diabetic renal injury, and EP₁ receptor deletion improves hyperfiltration, albuminuria, and fibrosis. The role of EP₁ receptors in hypertensive kidney disease (HKD) remains controversial. We examined the contribution of EP₁ receptors to HKD. EP₁ null (EP₁^-/-) mice were bred with hypertensive TTRhRen mice (Htn) to evaluate kidney function and injury at 24 weeks. EP₁ deletion had no effect on elevation of systolic blood pressure in Htn mice (HtnEP₁^-/-) but resulted in pronounced albuminuria and reduced FITC-inulin clearance, compared with Htn or wild-type (WT) mice. Ultrastructural injury to podocytes and glomerular endothelium was prominent in HtnEP₁^-/- mice; including widened subendothelial space, subendothelial lucent zones and focal lifting of endothelium from basement membrane, with focal subendothelial cell debris. Cortex COX2 mRNA was increased by EP₁ deletion. Glomerular EP₃ mRNA was reduced by EP₁ deletion, and EP₄ by Htn and EP₁ deletion. In WT mice, PGE₂ increased chloride reabsorption via EP₁ in isolated perfused thick ascending limb (TAL), but PGE₂ or EP₁ deletion did not affect vasopressin-mediated chloride reabsorption. In WT and Htn mouse inner medullary collecting duct (IMCD), PGE₂ inhibited vasopressin-water transport, but not in EP₁^-/- or HtnEP₁^-/- mice. Overall, EP₁ mediated TAL and IMCD transport in response to PGE₂ is unaltered in Htn, and EP₁ is protective in HKD.

AQP1 expression in the proximal tubule of diabetic rat kidney

Polyuria is a hallmark symptom and the first clinical manifestation of diabetes mellitus (DM). The glucose that remains in renal tubules was proposed to produce an osmotic effect resulting in polyuria. Although water is reabsorbed in proximal tubules through an aquaporin-1 (AQP1) dependent mechanism, AQP1 role in the genesis of polyuria is unknown. AQP1 expression was studied in a rat model of Type-1 DM at 15-days and 5-months of evolution. A different AQP1 expression pattern was found in both experimental groups, with no changes in AQP1 localization, suggesting that changes in AQP1 may be involved in the development of polyuria.

Arachidonic Acid Metabolism and Kidney Inflammation

As a major component of cell membrane lipids, Arachidonic acid (AA), being a major component of the cell membrane lipid content, is mainly metabolized by three kinds of enzymes: cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP450) enzymes. Based on these three metabolic pathways, AA could be converted into various metabolites that trigger different inflammatory responses. In the kidney, prostaglandins (PG), thromboxane (Tx), leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are the major metabolites generated from AA. An increased level of prostaglandins (PGs), TxA₂ and leukotriene B4 (LTB₄) results in inflammatory damage to the kidney. Moreover, the LTB₄-leukotriene B4 receptor 1 (BLT1) axis participates in the acute kidney injury via mediating the recruitment of renal neutrophils. In addition, AA can regulate renal ion transport through 19-hydroxystilbenetetraenoic acid (19-HETE) and 20-HETE, both of which are produced by cytochrome P450 monooxygenase. Epoxyeicosatrienoic acids (EETs) generated by the CYP450 enzyme also plays a paramount role in the kidney damage during the inflammation process. For example, 14 and 15-EET mitigated ischemia/reperfusion-caused renal tubular epithelial cell damage. Many drug candidates that target the AA metabolism pathways are being developed to treat kidney inflammation. These observations support an extraordinary interest in a wide range of studies on drug interventions aiming to control AA metabolism and kidney inflammation.

Identification of key genes involved in type 2 diabetic islet dysfunction: a bioinformatics study

Aims: To identify the key differentially expressed genes (DEGs) in islet and investigate their potential pathway in the molecular process of type 2 diabetes.

Methods: Gene Expression Omnibus (GEO) datasets (GSE20966, GSE25724, GSE38642) of type 2 diabetes patients and normal controls were downloaded from GEO database. DEGs were further assessed by enrichment analysis based on the Database for Annotation, Visualization and Integrated Discovery (DAVID) 6.8. Then, by using Search Tool for the Retrieval Interacting Genes (STRING) 10.0 and gene set enrichment analysis (GSEA), we identified hub gene and associated pathway. At last, we performed quantitative real-time PCR (qPCR) to validate the expression of hub gene.

Results: Forty-five DEGs were co-expressed in the three datasets, most of which were down-regulated. DEGs are mostly involved in cell pathway, response to hormone and binding. In protein–protein interaction (PPI) network, we identified ATP-citrate lyase (ACLY) as hub gene. GSEA analysis suggests low expression of ACLY is enriched in glycine serine and threonine metabolism, drug metabolism cytochrome P450 (CYP) and NOD-like receptor (NLR) signaling pathway. qPCR showed the same expression trend of hub gene ACLY as in our bioinformatics analysis.

Conclusion: Bioinformatics analysis revealed that ACLY and the pathways involved are possible target in the molecular mechanism of type 2 diabetes.

Mammalian urine concentration: a review of renal medullary architecture and membrane transporters

Mammalian kidneys play an essential role in balancing internal water and salt concentrations. When water needs to be conserved, the renal medulla produces concentrated urine. Central to this process of urine concentration is an osmotic gradient that increases from the corticomedullary boundary to the inner medullary tip. How this gradient is generated and maintained has been the subject of study since the 1940s. While it is generally accepted that the outer medulla contributes to the gradient by means of an active process involving countercurrent multiplication, the source of the gradient in the inner medulla is unclear. The last two decades have witnessed advances in our understanding of the urine-concentrating mechanism. Details of medullary architecture and permeability properties of the tubules and vessels suggest that the functional and anatomic relationships of these structures may contribute to the osmotic gradient necessary to concentrate urine. Additionally, we are learning more about the membrane transporters involved and their regulatory mechanisms. The role of medullary architecture and membrane transporters in the mammalian urine-concentrating mechanism are the focus of this review.

Prostaglandin E2 increases migration and proliferation of human glioblastoma cells by activating transient receptor potential melastatin 7 channels

Recent studies showed that both prostaglandin E2 (PGE2) and transient receptor potential melastatin 7 (TRPM7) play important roles in migration and proliferation of human glioblastoma cells. In this study, we tested the association between PGE2 and TRPM7. We found that PGE2 increased TRPM7 currents in HEK293 and human glioblastoma A172 cells. The PGE2 EP3 receptor antagonist L‐798106 abrogated the PGE2 stimulatory effect, while EP3 agonist 17‐phenyl trinor prostaglandin E2 (17‐pt‐PGE2) mimicked the effect of PEG2 on TRPM7. The TRPM7 phosphotransferase activity‐deficient mutation, K1646R had no effect on PGE2 induced increase of TRPM7 currents. Inhibition of protein kinase A (PKA) activity by Rp‐cAMP increased TRPM7 currents. TRPM7 PKA phosphorylation site mutation S1269A abolished the PGE2 effect on TRPM7 currents. PGE2 increased both mRNA and membrane protein expression of TRPM7 in A172 cells. Knockdown of TRPM7 by shRNA abrogated the PGE2 stimulated migration and proliferation of A172 cells. Blockage of TRPM7 with 2‐aminoethoxydiphenyl borate (2‐APB) or NS8593 had a similar effect as TRPM7‐shRNA. In conclusion, our results demonstrate that PGE2 activates TRPM7 via EP3/PKA signalling pathway, and that PGE2 enhances migration and proliferation of human glioblastoma cells by up‐regulation of the TRPM7 channel.

Prostaglandins in the pathogenesis of kidney diseases

Prostaglandins (PGs) are important lipid mediators produced from arachidonic acid via the sequential catalyzation of cyclooxygenases (COXs) and specific prostaglandin synthases. There are five subtypes of PGs, namely PGE2, PGI2, PGD2, PGF2α, and thromboxane A2 (TXA2). PGs exert distinct roles by combining to a diverse family of membrane-spanning G protein-coupled prostanoid receptors. The distribution of these PGs, their specific synthases and receptors vary a lot in the kidney. This review summarized the recent findings of PGs together with the COXs and their specific synthases and receptors in regulating renal function and highlighted the insights into their roles in the pathogenesis of various kidney diseases.

Role of mitochondrial oxidative stress in modulating the expressions of aquaporins in obstructive kidney disease

Downregulation of aquaporins (AQPs) in obstructive kidney disease has been well demonstrated with elusive mechanisms. Our previous study indicated that mitochondrial dysfunction played a crucial role in this process. However, it is still uncertain how mitochondrial dysfunction affected the AQPs in obstructive kidney disease. This study investigated the role of mitochondria-derived oxidative stress in mediating obstruction-induced downregulation of AQPs. After unilateral ureteral obstruction for 7 days, renal superoxide dismutase 2 (SOD2; mitochondria-specific SOD) was reduced by 85%. Meanwhile, AQP1, AQP2, AQP3, and AQP4 were remarkably downregulated as determined by Western blotting and/or quantitative real-time PCR. Administration of the SOD2 mimic manganese (III) tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP) significantly attenuated AQP2 downregulation in line with complete blockade of thiobarbituric acid-reactive substances elevation, whereas the reduction of AQP1, AQP3, and AQP4 was not affected. The cyclooxygenase (COX)-2/prostaglandin (PG) E2 pathway has been well documented as a contributor of AQP reduction in obstructed kidney; thus, we detected the levels of COX-1/2 and microsomal prostaglandin E synthase 1 (mPGES-1) in kidney and PGE2 secretion in urine. Significantly, MnTBAP partially suppressed the elevation of COX-2, mPGES-1, and PGE2. Moreover, a marked decrease of V2 receptor was significantly restored after MnTBAP treatment. However, the fibrotic response and renal tubular damage were unaffected by MnTBAP in obstructed kidneys. Collectively, these findings suggested an important role of mitochondrial oxidative stress in mediating AQP2 downregulation in obstructed kidney, possibly via modulating the COX-2/mPGES-1/PGE2/V2 receptor pathway.

PGE2 EP1 receptor inhibits vasopressin-dependent water reabsorption and sodium transport in mouse collecting duct

PGE2 regulates glomerular hemodynamics, renin secretion, and tubular transport. This study examined the contribution of PGE2 EP1 receptors to sodium and water homeostasis. Male EP1-/- mice were bred with hypertensive TTRhRen mice (Htn) to evaluate blood pressure and kidney function at 8 weeks of age in four groups: wildtype (WT), EP1-/-, Htn, HtnEP1-/-. Blood pressure and water balance were unaffected by EP1 deletion. COX1 and mPGE2 synthase were increased and COX2 was decreased in mice lacking EP1, with increases in EP3 and reductions in EP2 and EP4 mRNA throughout the nephron. Microdissected proximal tubule sglt1, NHE3, and AQP1 were increased in HtnEP1-/-, but sglt2 was increased in EP1-/- mice. Thick ascending limb NKCC2 was reduced in the cortex but increased in the medulla. Inner medullary collecting duct (IMCD) AQP1 and ENaC were increased, but AVP V2 receptors and urea transporter-1 were reduced in all mice compared to WT. In WT and Htn mice, PGE2 inhibited AVP-water transport and increased calcium in the IMCD, and inhibited sodium transport in cortical collecting ducts, but not in EP1-/- or HtnEP1-/- mice. Amiloride (ENaC) and hydrochlorothiazide (pendrin inhibitor) equally attenuated the effect of PGE2 on sodium transport. Taken together, the data suggest that EP1 regulates renal aquaporins and sodium transporters, attenuates AVP-water transport and inhibits sodium transport in the mouse collecting duct, which is mediated by both ENaC and pendrin-dependent pathways.