BACKGROUND:Although epigenetic modification of histone in embryonic development is well documented, its mechanistic role in the pathogenesis of hypertension is poorly understood. The purpose of this study is to investigate how histone 3 modification (H3K27me3 [trimethylation of histone 3 lysine 27]) in renal tubule cells regulates sodium excretion and blood pressure. METHODS:A mouse model of inducible renal tubule cell-specific deletion of KDM6A cKO (histone 3 lysine 27 demethylase 6A gene) was generated. RESULTS:Here, we uncovered the potential role of FBLN2 (fibulin 2) in the pathogenesis of epigenetic hypertension due to KDM6A cKO. KDM6A is a specific demethylase for H3K27me3. ChIP-seq analysis revealed that the H3K27me3 mark was increased in the promoter region of the FBLN2 gene, resulting in downregulation of FBLN2 protein expression in the kidney of KDM6A cKO mice. Treatment with rFBLN2 (recombinant FBLN2) largely attenuated blood pressure elevation, rescued impairment in sodium excretion, and prevented high salt-induced salt-sensitive hypertension in KDM6A cKO mice. Mechanistically, treatment with rFBLN2 rescued upregulation of NCC (Na-Cl cotransporter) and AQP2 (aquaporin 2) expression and decreased NKCC2 expression in renal tubular cells in the KDM6A cKO hypertensive mice. Intriguingly, FBLN2 may regulate NCC trafficking via forming an FBLN2/NCC complex, which decreases the cell membrane abundance of NCC by translocating NCC to the total membrane in distal convoluted tubule cells. CONCLUSIONS:These findings highlight a critical role of FBLN2 in the regulation of renal sodium excretion and blood pressure and suggest that FBLN2 deficiency may drive KDM6A deficiency-induced epigenetic hypertension. FBLN2 treatment may provide a new preventive and therapeutic strategy for salt-sensitive hypertension.

BACKGROUND:KDM6A (Lysine-Specific Demethylase 6A) is a specific demethylase for histone 3 lysine (K) 27 trimethylation (H3K27me3). The purpose of this study is to investigate whether KDM6A in renal tubule cells plays a role in the regulation of kidney function and blood pressure. METHODS:We first crossed Ksp-Cre+/- and KDM6Aflox/flox mice for generating inducible kidney-specific deletion of KDM6A gene. RESULTS:Notably, conditional knockout of KDM6A gene in renal tubule cells (KDM6A-cKO) increased H3K27me3 levels which leads to a decrease in Na excretion and elevation of blood pressure. Further analysis showed that the expression of NKCC2 (Na-K-2Cl cotransporter 2) and NCC (Na-Cl cotransporters) was upregulated which contributes to impaired Na excretion in KDM6A-cKO mice. The expression of AQP2 (aquaporin 2) was also increased in KDM6A-cKO mice, which may facilitate water reabsorption in KDM6A-cKO mice. The expression of Klotho was downregulated while expression of aging markers including p53, p21, and p16 was upregulated in kidneys of KDM6A-cKO mice, indicating that deletion of KDM6A in the renal tubule cells promotes kidney aging. Interestingly, KDM6A-cKO mice developed salt-sensitive hypertension which can be rescued by treatment with Klotho. KDM6A deficiency induced salt-sensitive hypertension likely through downregulation of the Klotho/ERK (extracellular signal-regulated kinase) signaling and upregulation of the WNK (with-no-lysine kinase) signaling. CONCLUSIONS:This study provides the first evidence that KDM6A plays an essential role in maintaining normal tubular function and blood pressure. Renal tubule cell specific KDM6A deficiency causes hypertension due to increased H3K27me3 levels and the resultant downregulation of Klotho gene expression which disrupts the Klotho/ERK/NCC/NKCC2 signaling.

The spontaneously hypertensive rat (SHR) is a commonly used animal model for studying primary hypertension. However, the precise mechanism of these rats developing hypertension remains to be defined. Here, we have first demonstrated that kidney stem cell reprogramming is a driver for the development of hypertension in SHR rats. In this study, we treated 5-week-old SHR rats with WKY-kidney stem cell-derived exosomes (WKY-Exo) and 5-week-old WKY rats with SHR-Exo, respectively, via i.p. injections. Notably, WKY-Exo effectively blocked the development of hypertension and arterial stiffening in SHRs. It is fascinating that WKY rats developed hypertension and arterial stiffening due to treatment of SHR-Exo. We confirmed that both WKY- and SHR-Exo were up taken into aortic endothelial and smooth muscle cells after i.p. delivery of CD63/GFP-labelled exosomes. We demonstrated that WKY-Exo can improve vascular functions and arterial compliance of SHR rats as evidenced by preventing the development of arterial stiffness and restoring renal artery endothelial function. We also demonstrated that the vascular functions were impaired in WKY rats after SHR-Exo treatment. Furthermore, our data show that expression of Elastin, Emilin1, and Myh11 was significantly downregulated in the aorta of SHR rats, which can be repaired by WKY-Exo treatment. SHR-Exo decreased expression of Elastin and Emilin1 without affecting Myh11 in the aorta of WKY rats, suggesting that Elastin and Emilin1 deficiency could contribute to arterial stiffening leading to the development of spontaneous hypertension. Proteomic analysis reveals the enrichment of protein-protein interaction network for elastic fiber assembling, blood vessel development, and regulation of angiogenesis in WKY-Exo vs SHR-Exo. In conclusion, our data first demonstrates that kidney stem cell reprograming is a driver for the development of spontaneous hypertension in SHR rats. WKY-KSCs-derived exosome contains a proteome profile promoting arterial repair, which may provide a therapeutic means to prevent and treat primary hypertension. NIH. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Epigenetics play a role in the development of hypertension. However, the precise mechanisms of how histone modification in renal tubule cells regulates blood pressure is largely undiscovered. In this study, we investigated the role of renal Kdm6a in salt-sensitive hypertension using a kidney tubular cell-specific Kdm6a gene knockout (Kdm6a cKO) mouse model. First, we demonstrated that knockout of Kdm6a in the renal tubular cells resulted in an increase of H3K27me3 associated with the development of hypertension in both male and female Kdm6a cKO mice. To explore the mechanism of H3K27me3-mediated hypertension, we performed a ChIP seq to identify the target genes of H3K27me3 in the renal tubular cells. Data showed that H3K27me3 regulated several physiological pathways in the renal tubular cells, including sodium transport in proximal convoluted tubule (PCT), and blood pressure regulation in distal convoluted tubule (DCT). Indeed, we found that the expressions of NCC, NKCC2, and AQP2 were upregulated in kidneys of Kdm6a cKO mice. Furthermore, ChIP seq data reveals that FBLN2, an extracellular matrix protein, appears to be a target of H3K27me3, which was downregulated in the kidney of Kdm6a cKO mice determined by real-time PCR, Western, and IHC. Notably, we demonstrated that FBLN2 abated high salt-induced hypertension through downregulation of NCC, NKCC2, and AQP2 in the tubular cells of Kdm6a cKO mice. Interestingly, pre-treatment of FBLN2 prevented salt-sensitive hypertension in these mice. Additionally, we have provided evidence that FBLN2 may regulate blood pressure through mediating the NCC cell membrane trafficking. Using a super high-resolution microscopy, we demonstrated that FBLN2 reduced levels of cell surface NCC in DCT cells cultured in hypotonic medium. Here, we have first demonstrated that FBLN2 may be a target gene of H3K27me3 in epigenetic-mediated hypertension. FBLN2 treatment may prevent and treat salt-sensitive hypertension. NIH This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

De Novo Generation of Kidney Organoids Using Adult Kidney Stem Cells Generation of kidney organoids using autologous kidney stem cells represents an attractive strategy for treating and potentially replacing the failing kidneys. In article number 2104034, Xiaobin Han and Zhongjie Sun report a previously unidentified adult kidney Sca1+ Oct4+ stem cells. Interestingly, culturing these stem cells led to de novo generation of self-organizing nephrons and kidney-like structures. This finding provides the first evidence that kidney stem cells are capable of de novo generating kidney organoids. This finding also offers a new opportunity for studying mammalian kidney development and personalized kidney regeneration.

Generation of kidney organoids using autologous kidney stem cells represents an attractive strategy for treating and potentially replacing the failing kidneys. However, whether adult mammalian kidney stem cells have regenerative capacity remains unknown. Here, previously unidentified adult kidney Sca1+ Oct4+ stem/progenitor cells are isolated. Interestingly, culturing these cells leads to generation of kidney-like structures. First, the assembly of self-organizing 3D kidney-like structures is observed. These kidney organoids contain podocytes, proximal tubules, and endothelial cells that form networks of capillary loop-like structures. Second, the differentiation of kidney stem cells into functionally mature tubules and self-organizing kidney-shaped structures in monolayer culture that selectively endocytoses dextran, is shown. Finally, the de novo generation of an entire self-organizing nephron from monolayer cultures is observed. Mechanistically, it is demonstrated that Sirt2-mediated canonical Wnt/β-catenin signaling is critical for the development of kidney organoids. Thus, the first evidence is provided that the adult mouse kidney stem cells are capable of de novo generating kidney organoids.

The physiological function of kidney stem cell‐derived extracellular vesicles remains elusive. Most recently, we isolated kidney stem cells (KSCs) from adult mouse kidneys and demonstrated that KSCs‐derived exosomes normalized blood pressure and improved kidney functions in hypertensive aged mice. To study if KSCs‐derived exosomes play a role in nephron repair and regeneration, we treated aged mice with CD63‐GFP labelled KSC‐exosome (CD63/GFP KSC‐Exo) (~1.0×1011particles/mouse) and traced CD63/GFP KSC‐Exo in the kidney. We found that KSC‐exosomes were mainly detected in the proximal and distal tubular cells near the damaged glomerulus in cortex area of the aging kidney. BrdU tracing study showed that BrdU positive cells were mainly detected in the glomerulus and co‐located with Ki67 cell proliferation marker in the kidney of KSC‐exosome treated mice. KSC‐exosome treatment also increased numbers of Sca1+cells surrounding the glomerulus area of aging kidney. Interestingly, the glomerular filtration rate (GFR) was significantly increased in KSC‐exosome‐treated aged mice, suggesting improved glomerular function. To explore the mechanisms how KSC‐exosome improves kidney functions, we performed proteome analysis of KSC‐exosomes by mass spectrometry. We found several pathways that involve in the kidney development were upregulated in the KSC‐exosome from adult mice compared to that of aged mice. Notably, we further identified that FBLN2, an extracellular matrix protein, plays an important role in aging‐associated hypertension. We showed that expression of FBLN2 was downregulated in the kidney of aged mice and recombinant FBLN2 (rFBLN2) treatment normalized blood pressure and improved GFR of hypertensive aged mice. Furthermore, we found that FBLN2 is mainly located in the basement membrane of glomerulus (GBM). The thickness of GBM was increased in aged mice determined by TEM. KSC‐exosome or rFBLN2 treatment reduced the thickness of GBM, suggesting that FBLN2 may play an important role in maintaining the integrity of GBM and kidney functions. In conclusion, our finding provided the first evidence that the adult mouse kidney stem cell‐derived exosomes play an important role in nephron repair and regeneration partly via FBLN2. KSC‐exosome treatment may be a novel therapeutic strategy for hypertension‐associated kidney injuries in aging.

End‐stage renal disease affects an estimated 2.4 million people annually worldwide. With cases increasing 8% every year, regenerative strategies are needed to help alleviate, and potentially replace, the increasing demand for kidney transplants. An important question remains whether stem cells reside in the adult mammalian kidney. Here we developed a methodology for isolation of kidney stem cells from adult mouse kidney by using Sca1 and Oct4 stem cell markers. Using these cells, we generated three types of kidney‐like structures. First, we observed the assembly of self‐organizing three‐dimensional kidney organoids. These kidney organoids show characteristic of kidney structures and contain podocytes and endothelial cells that form networks of capillary loop‐like structures. We also observed the de novogeneration of a self‐organizing nephron (and its associated collecting duct) from monolayer cultures. Comma‐ and S‐shaped bodies that expressed activated Notch1 were present during this formation, suggesting that Notch signaling played a key role in driving nephrogenesis. This is consistent with our current knowledge of nephron formation in the mouse embryo. Furthermore, we observed the differentiation of monolayer cells into functionally mature tubules and self‐organizing kidney‐shaped structures that selectively endocytose dextran. Finally, we demonstrated that expression of Sirt2 was upregulated, which modulated the dynamics of canonical Wnt/β‐catenin signaling during kidney organoid development. Altogether, our observations provide the first evidence for the existence of stem cells in the adult mouse kidney. These findings offer powerful tools for future applications, including drug screening, disease modelling, cell therapy, and kidney regeneration.

The physiological function of stem cell-derived extracellular vesicles remains elusive. Most recently, we isolated kidney stem cells (KSC) from adult mouse kidneys and studied the role of KSC-derived exosomes in blood pressure regulation in hypertensive aged mice. We treated aged mice with KSC-exosome (~1.26×1011 ± 1.94×109 particles/mouse/day) or PBS by intraperitoneal injection for 5 days. We found that the blood pressure was reduced (from 150.8±12.2 to 128.6±3 mmHg) at day 6 in KSC-exosome-treated aged mice, while the blood pressure remained unchanged in PBS-treated aged mice. Blood pressure continued to decrease to 116±8.2 mmHg at day 14 after KSC-exosome treatment. Hypertension reemerged gradually and relapsed at day 28 after treatment. To assess the kidney functions, we collected 6-hour urine at day 5 of the treatment. KSC-exosome treatment significantly reduced the increases in urine albumin and creatinine in aged mice, indicating that KSC-exosomes improve aging-associated kidney dysfunction. Notably, the glomerular filtration rate (GFR) was significantly increased in KSC-exosome-treated aged mice, suggesting improved glomerular function. Urinary cytokine levels were increased in aged mice which were largely reduced by KSC-exosomes. KSC-exosomes effectively reduced the kidney injury markers TIM1 and adiponectin and inflammation marker NGAL which were confirmed by ELISA. These data suggest that KSC-exosome treatment attenuates aging-associated renal inflammation and kidney injury. To explore the mechanisms by which KSC-exosome attenuates blood pressure and improves kidney functions in aged mice, we performed proteome analysis of KSC-exosomes by mass spectrometry. We found several pathways that involve in the kidney development were upregulated in KSC-exosome compared to renal tubule cells (RTC) derived-exosomes. Interestingly, KSC-exosome induced cell proliferation and cell migration after injury possibly through activation of AKT signaling demonstrated in vitro. In conclusion, our finding provided the first evidence that the adult mouse kidney stem cell-derived exosomes attenuate aging-associated hypertension and kidney dysfunctions. KSC-exosome treatment may be a novel therapeutic strategy for hypertension-associated kidney injuries in aging.

KL (klotho) levels decline with age, which is an important mechanistic driver of aging. KL gene deficiency is associated with hypertension. The purpose of this study is to investigate the potential role of H3K27me3 (histone 3 lysine [K] 27 trimethylation) in the regulation of KL gene expression and examine the related molecular pathways that may drive kidney cell aging. Kidneys were collected from 6-month-old WT (wild type; young WT), 30-month-old WT (aged WT), and 6- (young) and 20-month-old (aged) KL mutant mice, respectively. We demonstrated that the H3K27me3 level was increased in kidneys of aged WT and KL mutant mice versus young WT mice. Elevation of H3K27me3 levels was likely due to downregulation of the H3K27 (histone H3 Lys 27)-specific demethylase JMJD3 (the Jumonji domain containing-3) in the aged kidneys. Inhibition of PRC2 (polycomb repressive complex C2; histone trimethyltransferase) decreased the H3K27me3 levels leading to an increase in the expression of KL in cultured primary renal tubule cells assessed by Western blot and KL promoter activity assays. The chromatin immunoprecipitation qPCR assay revealed that H3K27me3 was physically associated with the KL promoter region. Furthermore, aging impaired the SGK1 (serum- and glucocorticoid-induced protein kinase 1)/FOXO3a (the forkhead box class O 3a) signaling leading to upregulation of p53 and p16 (aging markers) in the kidney of aged WT mice. KL may regulate the SGK1/FOXO3 signaling, which was decreased due to KL deficiency. Thus, aging-associated downregulation of KL gene expression may be partly attributed to upregulation of H3K27me3 levels. Downregulation of KL may impair the SGK1/FOXO3 signaling contributing to kidney cell aging.

Objective: Aging-associated downregulation of Klotho is partly due to epigenetic upregulation of H3K27me3 in the kidney. The purpose of this study is to investigate the potential role of KDM6a, a demethylase of histone 3 lysine (K) 27 trimethylation (H3K27me3), in the regulation of blood pressure and explore the related molecular pathways that may influence the kidney function during aging. Methods and Results: Wild type and Ksp-Cre/KDM6a-floxed mice were divided into vehicle control and tamoxifen (10 mg/kg/mouse/7days) treated cohorts (WT mice: KDM6a floxed or Ksp-Cre only and Ksp-Cre/KDM6a -loxed mice). Blood pressure (BP) was measured by tail cuff method and confirmed by carotid artery cannulation at the end of study. Deletion of the KDM6a gene (KDM6a-cKO) significantly increased BP at day 7. BP remained elevated throughout the study. We found that the H3K27me3 level was significantly increased in the kidneys of KDM6a-cKO mice compared to control mice confirming that KDM6a is an important H3K27 demethylase in the control of methylation levels in the kidney. Elevation of BP was likely due to upregulation of the Na + :K + :2Cl - co-transporter (NKCC2) in the thick ascending limb of Henle's loop and NaCl co-transporter (NCC) in the distal convoluted tubule confirmed by qPCR and immunohistochemistry. Accordingly, we found that the urine sodium level was decreased in KDM6a-cKO mice compared to KDM6a-con mice. We showed that expression of aquaporin 2 (AQP2) was increased in the kidney of KDM6a-cKO mice, suggesting that AQP2 may also contribute to increased BP through modulation of body water homeostasis. Furthermore, we demonstrated that expression of Klotho was downregulated by 50%, which blocked FGFR1/Klotho/ERK signaling in the kidney of KDM6a-cKO mice. Notably, expression of aging markers including p53, p21, and p16 was significantly increased in the kidney of KDM6a-cKO mice, indicating that deletion of KDM6a in the renal tubule results in kidney aging. Conclusion: KDM6A is essential to the maintenance of normal kidney function and blood pressure. Renal-specific KDM6A knockout-induced hypertension is likely attributed to increased H3K27me3 levels and the resultant dowregulation of Klotho gene expression which impairs the FGFR1/Klotho/ERK signaling.

Taurine transporter (TauT) has been identified as a target gene of p53 tumor suppressor. TauT is also found to be overexpressed in variety type of human cancers, such as leukemia. This study showed that expression of TauT was upregulated by c-Myc and c-Jun oncogenes. To explore whether blocking of TauT inhibits tumor development, the RNA interference (RNAi) and immune targeting approaches were tested in tumor cells in vitro and in p53 mutant mice in vivo. Knockdown of TauT expression by RNAi resulted in cell cycle G2 arrest and suppressed human breast cancer MCF-7 cells proliferation determined by colonies production and cell migration assays. Knockdown of TauT also rendered MCF-7 cells more susceptible to chemotherapeutic drug-induced apoptosis. An antibody specifically against TauT blocked taurine uptake and induced cell cycle G2 arrest leading to cell death of variety type of tumor cells without affecting the viability of normal mammalian cells. TauT peptide vaccination significantly increased median lifespan (1.5-fold) of the p53 null mice and rescued p53+/− mice by extending the median lifespan from 315 days to 621 days. Furthermore, single dose treatment of tumor-bearing (thymic lymphoma) p53 null mice with TauT peptide reduced tumor size by about 50% and significantly prolonged survival of these mice from average 7 days (after observing the thymic lymphoma) to 21 days. This finding demonstrates that a novel TauT peptide vaccine can delay, inhibit, and/or treat p53 mutation related spontaneous tumorigenesis in vivo. Therefore, TauT peptide may be used as a universal cancer vaccine to prevent and/or treat patients with p53 mutation-mediated cancers.

There is controversy regarding whether excess FGF23 causes left ventricular hypertrophy (LVH) directly through activation of fibroblast growth factor receptor 4 (FGFR4) in cardiomyocytes or indirectly through reductions in soluble Klotho (sK). We investigated the respective roles of myocardial FGFR4 and sKL in mediating FGF23-induced LVH using mouse genetic and pharmacological approaches. To investigate a direct role of myocardial FGFR4 in mediating the cardiotoxic effects of excess circulating FGF23, we administered rFGF23 to mice with cardiac-specific loss of FGFR4 (FGFR4 heart-cKO). We tested a model of sKL deficiency, hypertension and LVH created by the conditional deletion of FGFR1 in the renal distal tubule (FGFR1DT cKO mice). The cardioprotective effects of sKL in both mouse models was assessed by the systemic administration of recombinant sKL. We confirmed that FGF23 treatment activates PLCγ in the heart and induces LVH in the absence of membrane α-Klotho. Conditional deletion of FGFR4 in the myocardium prevented rFGF23-induced LVH in mice, establishing direct cardiotoxicity of FGF23 through activation of FGFR4. Recombinant sKL administration prevented LVH, but not HTN, in FGFR1DT cKO mice, consistent with direct cardioprotective effects. Co-administration of recombinant sKL with FGF23 in culture inhibited rFGF23-induced p-PLCγ signaling. Thus, FGF23 ability to include LVH represents a balance between FGF23 direct cardiac activation of FGFR4 and the modulating effects of circulating sKL to alter FGF23-dependent myocardial signaling pathways.

Both the activation of the renin angiotensin aldosterone system (RAAS) and elevations of circulating Fibroblast Growth Factor-23 (FGF-23) have been implicated in the pathogenesis of left ventricular hypertrophy (LVH) in chronic kidney disease. To investigate potential cross-talk between RAAS and FGF-23, we administered angiotensin II (Ang II) to wild-type rodents and the Hyp mouse model of excess FGF-23. Ang II administration for four weeks to wild-type rodents resulted in significant increases in systolic blood pressure and LVH. Unexpectedly, FGF-23 circulating levels were increased by 1.5–1.7 fold in Ang II treated animals. In addition, Ang II treatment increased expression of FGF-23 message levels in bone, the predominant tissue for FGF-23 production, and induced expression of FGF-23 and its co-receptor α-Klotho in the heart, which normally does not express FGF-23 or α-Klotho in physiologically relevant levels. Hyp mice with elevated FGF-23 exhibited increased blood pressure and LVH at baseline. Ang II administration to Hyp mice resulted further increments in blood pressure and left ventricular hypertrophy, consistent with additive cardiovascular effects. These findings suggest that FGF-23 may participate in unexpected systemic and paracrine networks regulating hemodynamic and myocardial responses.

Fibroblast growth factor-23 (FGF-23) is a bone-derived hormone that activates FGFR/α-Klotho binary complexes in the kidney renal tubules to regulate phosphate reabsorption and vitamin D metabolism. The objective of this review is to discuss the emerging data that show that FGF-23 has functions beyond regulation of mineral metabolism, including roles in innate immune and hemodynamic responses. Excess FGF-23 is associated with inflammation and adverse infectious outcomes, as well as increased morbidity and mortality, particularly in patients with chronic kidney disease. Enhancer elements in the FGF-23 promoter have been identified that mediate the effects of inflammatory cytokines to stimulate FGF-23 gene transcription in bone. In addition, inflammation induces ectopic expression of FGF-23 and α-Klotho in macrophages that do not normally express FGF-23 or its binary receptor complexes. These observations suggest that FGF-23 may play an important role in regulating innate immunity through multiple potential mechanisms. Circulating FGF-23 acts as a counter-regulatory hormone to suppress 1,25D production in the proximal tubule of the kidney. Since vitamin D deficiency may predispose infectious and cardiovascular diseases, FGF-23 effects on innate immune responses may be due to suppression of 1,25D production. Alternatively, systemic and locally produced FGF-23 may modulate immune functions through direct interactions with myeloid cells, including macrophages and polymorphonuclear leukocytes to impair immune cell functions. Short-acting small molecules that reversibly inhibit FGF-23 offer the potential to block pro-inflammatory and cardiotoxic effects of FGF-23 with less side effects compared with FGF-23 blocking antibodies that have the potential to cause hyperphosphatemia and soft tissue calcifications in animal models. In conclusion, there are several mechanisms by which FGF-23 impacts the innate immune system and further investigation is critical for the development of therapies to treat diseases associated with elevated FGF-23.

The bone-derived hormone fibroblast growth factor-23 (FGF-23) activates complexes composed of FGF receptors (FGFRs), including FGFR1, and α-Klotho in the kidney distal tubule (DT), leading to increased sodium retention and hypertension. However, the role of FGFR1 in regulating renal processes linked to hypertension is unclear. Here, we investigated the effects of selective FGFR1 loss in the DT. Conditional knockout (cKO) of FGFR1 in the DT (FGFR1DT-cKO mice) resulted in left ventricular hypertrophy (LVH) and decreased kidney expression of α-Klotho in association with enhanced BP, decreased expression of angiotensin converting enzyme 2, and increased expression of the Na+-K+-2Cl- cotransporter. Notably, recombinant FGF-23 administration similarly decreased the kidney expression of α-Klotho and induced LVH in mice. Pharmacologic activation of FGFR1 with a monoclonal anti-FGFR1 antibody (R1MAb1) normalized BP and significantly attenuated LVH in the Hyp mouse model of excess FGF-23, but did not induce a response in FGFR1DT-cKO mice. The hearts of FGFR1DT-cKO mice showed increased expression of the transient receptor potential cation channel, subfamily C, member 6 (TRPC6), consistent with cardiac effects of soluble Klotho deficiency. Moreover, administration of recombinant soluble Klotho lowered BP in the Hyp mice. Thus, FGFR1 in the DT regulates systemic hemodynamic responses opposite to those predicted by the actions of FGF-23. These cardiovascular effects appear to be mediated by paracrine FGF control of kidney FGFR1 and subsequent regulation of soluble Klotho and TRPC6. FGFR1 in the kidney may provide a new molecular target for treating hypertension.

Purpose of reviewThis review examines the role of fibroblast growth factor-23 (FGF-23) in mineral metabolism, innate immunity and adverse cardiovascular outcomes.Recent findingsFGF-23, produced by osteocytes in bone, activates FGFR/-Klotho (-Kl) complexes in the kidney. The resulting bone-kidney axis coordinates renal phosphate reabsorption with bone mineralization, and creates a counter-regulatory feedback loop to prevent vitamin D toxicity. FGF-23 acts to counter-regulate the effects of vitamin D on innate immunity and cardiovascular responses. FGF-23 is ectopically expressed along with -Kl in activated macrophages, creating a proinflammatory paracrine signaling pathway that counters the antiinflammatory actions of vitamin D. FGF-23 also inhibits angiotensin-converting enzyme 2 expression and increases sodium reabsorption in the kidney, leading to hypertension and left ventricular hypertrophy. Finally, FGF-23 is purported to cause adverse cardiac and impair neutrophil responses through activation of FGFRs in the absence of -Kl. Although secreted forms of -Kl have FGF-23 independent effects, the possibility of -Kl independent effects of FGF-23 is controversial and requires additional experimental validation.SummaryFGF-23 participates in a bone-kidney axis regulating mineral homeostasis, proinflammatory paracrine macrophage signaling pathways, and in a bone-cardio-renal axis regulating hemodynamics that counteract the effects of vitamin D.

Mechanisms underlying the association between fibroblastic growth factor 23 (FGF‐23) and inflammation are uncertain. We found that FGF‐23 was markedly up‐regulated in LPS/INF‐γ‐induced proinflammatory M1 macrophages and Hyp mouse‐derived peritoneal macrophages, but not in IL‐4‐induced M2 anti‐inflammatory macrophages. NF‐КB and JAK/STAT1 pathways mediated the increased transcription of FGF‐23 in response to M1 polarization. FGF‐23 stimulated TNF‐α, but not IL‐6, expression in M0 macrophages and suppressed Arginase‐1 expression in M2 macrophages through FGFR‐mediated mechanisms. 1,25(OH)2D stimulated Arginase‐1 expression and inhibited FGF‐23 stimulation of TNF‐α. FGF‐23 has proinflammatory paracrine functions and counter‐regulatory actions to 1,25(OH)2D on innate immune responses.

A postnatal role of fibroblast growth factor receptor-1 (FGFR1) in the kidney is suggested by its binding to α-Klotho to form an obligate receptor for the hormone fibroblast growth factor-23 (FGF-23). FGFR1 is expressed in both the proximal and distal renal tubular segments, but its tubular specific functions are unclear. In this study, we crossed Fgfr1flox/flox mice with either gamma-glutamyltransferase-Cre (γGT-Cre) or kidney specific-Cre (Ksp-Cre) mice to selectively create proximal tubule (PT) and distal tubule (DT) Fgfr1 conditional knockout mice (designated Fgfr1PT-cKO and Fgfr1DT-cKO, respectively). Fgfr1PT-cKO mice exhibited an increase in sodium-dependent phosphate co-transporter expression, hyperphosphatemia, and refractoriness to the phosphaturic actions of FGF-23, consistent with a direct role of FGFR1 in mediating the proximal tubular phosphate responses to FGF-23. In contrast, Fgfr1DT-cKO mice unexpectedly developed hypercalciuria, secondary elevations of parathyroid hormone (PTH), hypophosphatemia and enhanced urinary phosphate excretion. Fgfr1PT-cKO mice also developed a curly tail/spina bifida-like skeletal phenotype, whereas Fgfr1DT-cKO mice developed renal tubular micro-calcifications and reductions in cortical bone thickness. Thus, FGFR1 has dual functions to directly regulate proximal and distal tubule phosphate and calcium reabsorption, indicating a physiological role of FGFR1 signaling in both phosphate and calcium homeostasis.