Kidney-Specific Klotho Gene Deletion Causes Aortic Aneurysm via Hyperphosphatemia

Sexually dimorphic renal expression of mouse Klotho is directed by a kidney-specific distal enhancer responsive to HNF1b

Transcription enhancers are genomic sequences regulating common and tissue-specific genes and their disruption can contribute to human disease development and progression. Klotho, a sexually dimorphic gene specifically expressed in kidney, is well-linked to kidney dysfunction and its deletion from the mouse genome leads to premature aging and death. However, the sexually dimorphic regulation of Klotho is not understood. Here, we characterize two candidate Klotho enhancers using H3K27ac epigenetic marks and transcription factor binding and investigate their functions, individually and combined, through CRISPR-Cas9 genome engineering. We discovered that only the distal (E1), but not the proximal (E2) candidate region constitutes a functional enhancer, with the double deletion not causing Klotho expression to further decrease. E1 activity is dependent on HNF1b transcription factor binding site within the enhancer. Further, E1 controls the sexual dimorphism of Klotho as evidenced by qPCR and RNA-seq. Despite the sharp reduction of Klotho mRNA, unlike germline Klotho knockouts, mutant mice present normal phenotype, including weight, lifespan, and serum biochemistry. Lastly, only males lacking E1 display more prominent acute, but not chronic kidney injury responses, indicating a remarkable range of potential adaptation to isolated Klotho loss, especially in female E1 knockouts, retaining renoprotection despite over 80% Klotho reduction.

Systematic Mendelian Randomization Exploring Druggable Genes for Hemorrhagic Strokes

Patients with hemorrhagic stroke have high rates of morbidity and mortality, and drugs for prevention are very limited. Mendelian randomization (MR) analysis can increase the success rate of drug development by providing genetic evidence. Previous MR analyses only analyzed the role of individual drug target genes in hemorrhagic stroke; therefore, we used MR analysis to systematically explore the druggable genes for hemorrhagic stroke. We sequentially performed summary-data-based MR analysis and two-sample MR analysis to assess the associations of all genes within the database with intracranial aneurysm, intracerebral hemorrhage, and their subtypes. Validated genes were further analyzed by colocalization. Only genes that were positive in all three analyses and were druggable were considered desirable genes. We also explored the mediators of genes affecting hemorrhagic stroke incidence. Finally, the associations of druggable genes with other cardiovascular diseases were analyzed to assess potential side effects. We identified 56 genes that significantly affected hemorrhagic stroke incidence. Moreover, TNFSF12, SLC22A4, SPARC, KL, RELT, and ADORA3 were found to be druggable. The inhibition of TNFSF12, SLC22A4, and SPARC can reduce the risk of intracranial aneurysm, subarachnoid hemorrhage, and intracerebral hemorrhage. Gene-induced hypertension may be a potential mechanism by which these genes cause hemorrhagic stroke. We also found that blocking these genes may cause side effects, such as ischemic stroke and its subtypes. Our study revealed that six druggable genes were associated with hemorrhagic stroke, and the inhibition of TNFSF12, SLC22A4, and SPARC had preventive effects against hemorrhagic strokes.

Sexually dimorphic renal expression of Klotho is directed by a kidney-specific distal enhancer responsive to HNF1b

Transcription enhancers are genomic sequences regulating common and tissue-specific genes and their disruption can contribute to human disease development and progression. Klotho, a sexually dimorphic gene specifically expressed in kidney, is well-linked to kidney dysfunction and its deletion from the mouse genome leads to premature aging and death. However, the sexually dimorphic regulation of Klotho is not understood. Here, we characterize two candidate Klotho enhancers using H3K27ac epigenetic marks and transcription factor binding and investigate their functions, individually and combined, through CRISPR-Cas9 genome engineering. We discovered that only the distal (E1), but not the proximal (E2) candidate region constitutes a functional enhancer, with the double deletion not causing Klotho expression to further decrease. E1 activity is dependent on HNF1b transcription factor binding site within the enhancer. Further, E1 controls the sexual dimorphism of Klotho as evidenced by qPCR and RNA-seq. Despite the sharp reduction of Klotho mRNA, unlike germline Klotho knockouts, mutant mice presented normal phenotype, including weight, lifespan, and serum biochemistry. Lastly, only males lacking E1 display more prominent acute, but not chronic kidney injury responses, indicating a remarkable range of potential adaptation to isolated Klotho loss, especially in female E1 knockouts, retaining renoprotection despite over 80% Klotho reduction.

Sexually dimorphic renal expression of Klotho is directed by a kidney-specific distal enhancer responsive to HNF1b

Transcription enhancers are genomic sequences regulating common and tissue-specific genes and their disruption can contribute to human disease development and progression. Klotho, a sexually dimorphic gene specifically expressed in kidney, is well-linked to kidney dysfunction and its deletion from the mouse genome leads to premature aging and death. However, the sexually dimorphic regulation of Klotho is not understood. Here, we characterize two candidate Klotho enhancers using H3K27ac epigenetic marks and transcription factor binding and investigate their functions, individually and combined, through CRISPR-Cas9 genome engineering. We discovered that only the distal (E1), but not the proximal (E2) candidate region constitutes a functional enhancer, with the double deletion not causing Klotho expression to further decrease. E1 activity is dependent on HNF1b transcription factor binding site within the enhancer. Further, E1 controls the sexual dimorphism of Klotho as evidenced by qPCR and RNA-seq. Despite the sharp reduction of Klotho mRNA, unlike germline Klotho knockouts, mutant mice presented normal phenotype, including weight, lifespan, and serum biochemistry. Lastly, only males lacking E1 display more prominent acute, but not chronic kidney injury responses, indicating a remarkable range of potential adaptation to isolated Klotho loss, especially in female E1 knockouts, retaining renoprotection despite over 80% Klotho reduction.

KDM6A Demethylase Regulates Renal Sodium Excretion and Blood Pressure

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.

Inhibition of miR-101-3p prevents human aortic valve interstitial cell calcification through regulation of CDH11/SOX9 expression

BACKGROUND

Calcific aortic valve disease (CAVD) is the second leading cause of adult heart diseases. The purpose of this study is to investigate whether miR-101-3p plays a role in the human aortic valve interstitial cells (HAVICs) calcification and the underlying mechanisms.

METHODS

Small RNA deep sequencing and qPCR analysis were used to determine changes in microRNA expression in calcified human aortic valves.

RESULTS

The data showed that miR-101-3p levels were increased in the calcified human aortic valves. Using cultured primary HAVICs, we demonstrated that the miR-101-3p mimic promoted calcification and upregulated the osteogenesis pathway, while anti-miR-101-3p inhibited osteogenic differentiation and prevented calcification in HAVICs treated with the osteogenic conditioned medium. Mechanistically, miR-101-3p directly targeted cadherin-11 (CDH11) and Sry-related high-mobility-group box 9 (SOX9), key factors in the regulation of chondrogenesis and osteogenesis. Both CDH11 and SOX9 expressions were downregulated in the calcified human HAVICs. Inhibition of miR-101-3p restored expression of CDH11, SOX9 and ASPN and prevented osteogenesis in HAVICs under the calcific condition.

CONCLUSION

miR-101-3p plays an important role in HAVIC calcification through regulation of CDH11/SOX9 expression. The finding is important as it reveals that miR-1013p may be a potential therapeutic target for calcific aortic valve disease.

Aging impairs arterial compliance via Klotho-mediated downregulation of B-cell population and IgG levels

OBJECTIVE

Aging is associated with compromised immune function and arterial remodeling and stiffness. The purpose of this study is to investigate whether in vivo AAV-based delivery of secreted Klotho (SKL) gene (AAV-SKL) improves aging- and senescence-associated immune dysfunction and arterial stiffness.

METHODS AND RESULTS

Senescence-accelerated mice prone strain 1 (SAMP1, 10 months) and old mice (20 months) were used. Serum SKL levels, B-cell population and serum IgG levels were markedly decreased in SAMP1 and old mice. Rescue of downregulation of serum SKL levels by in vivo AAV2-based delivery of SKL gene (AAV-SKL) increased B-cell population and serum IgG levels and attenuated arterial stiffness in SAMP1 and old mice. Thus, Klotho deficiency may play a role in senescence- and aging-associated humoral immune dysfunction and arterial stiffness. Vascular infiltration of inflammatory cells and expression of TGFβ1, collagen 1, scleraxis, MMP-2 and MMP-9 were increased while the elastin level was decreased in aortas of SAMP1 and old mice which can be rescued by AAV-SKL. Interestingly, treatment with IgG effectively rescued arterial inflammation and remodeling and attenuated arterial stiffness and hypertension in aging mice. In cultured B-lymphoblast cells, we further showed that SKL regulates B-cell proliferation and maturation partly via the NFkB pathway.

CONCLUSION

Aging-associated arterial stiffening may be largely attributed to downregulation of B-cell population and serum IgG levels. AAV-SKL attenuates arterial stiffness in aging mice partly via restoring B-cell population and serum IgG levels which attenuates aging-associated vascular inflammation and arterial remodeling.

In Vivo Cardiac-specific Expression of Adenylyl Cyclase 4 Gene Protects against Klotho Deficiency-induced Heart Failure

Klotho is an aging-suppressor gene. Klotho gene deficiency causes heart failure in Klotho-hypomorphic mutant (KL (-/-)) mice. RNA-seq and western blot analysis showed that adenylyl cyclase type IV (AC4) mRNA and protein expression was largely decreased in cardiomyocytes of KL (-/-) mice. The objective of this study was to investigate whether in vivo cardiac-specific expression of AC4 gene protects against Klotho deficiency-induced heart failure. Interestingly, in vivo AAV-based cardiac-specific AC4 gene expression increased left ventricular fractional shortening, ejection fraction, stroke volume, and left ventricular end-diastolic volume in KL (-/-) mice, suggesting that cardiac-specific AC4 gene expression improves Klotho deficiency-induced heart dysfunction. Cardiac-specific AC4 gene expression also decreased Klotho deficiency-induced cardiac hypertrophy. Cardiac-specific AC4 gene expression alleviated Klotho deficiency-induced cardiac fibrosis and calcification. Furthermore, cardiac-specific AC4 gene expression attenuated mitochondrial dysfunction, superoxide accumulation and cardiomyocyte apoptotic cell death. Thus, downregulation of AC4 may contribute to Klotho deficiency-induced heart failure. Mechanistically, AAV2/9-αMHC-AC4 increased cardiomyocytic cAMP levels and thus regulated the PKA-PLN-SERCA2 signal pathway, which is critical in modulating calcium flux and mitochondrial function. In conclusion, cardiac-specific AC4 gene expression protects against Klotho deficiency-induced heart failure through increasing cardiomyocytic cAMP levels, which alleviates cAMP-dependent mitochondrial dysfunction, superoxide accumulation and apoptotic cell death. AC4 regulates superoxide levels via the cAMP-PKA pathway. AC4 could be a potential therapeutic target for heart failure associated with Klotho deficiency. Heart failure is the major cause of mortality in patients with chronic kidney disease (CKD). A decrease in Klotho levels is linked to CKD.

Adult Mouse Kidney Stem Cells Orchestrate the De Novo Assembly of a Nephron via Sirt2-Modulated Canonical Wnt/β-Catenin Signaling

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.

Estrogen inhibits renal Na-Pi Co-transporters and improves klotho deficiency-induced acute heart failure

Objective and hypothesis

Klotho is an aging-suppressor gene. Mutation of Klotho gene causes hyperphosphatemia and acute heart failure. However, the relationship of hyperphosphatemia and acute heart failure is unclear. We hypothesize that hyperphosphatemia mediates Klotho deficiency-induced acute heart failure and further that therapeutic reduction of hyperphosphatemia prevents acute heart failure in Klotho mutant (KL(−/−)) mice.

Methods and results

A significant elevation of serum phosphorus levels and a large reduction of heart function were found in KL(−/−) mice by six weeks of age. Normalization of serum phosphorus levels by low phosphate diet (LPD) rescued Klotho deficiency-induced heart failure and extended lifespan in male mice. Klotho deficiency impaired cardiac mitochondrial respiratory enzyme function and increased superoxide production, oxidative stress, and cardiac cell apoptosis in male KL(−/−) mice which can be eliminated by LPD. LPD, however, did not rescue hyperphosphatemia or heart failure in female KL(−/−) mice. LPD did not affect estrogen depletion in female KL(−/−) mice. Normalization of serum estrogen levels by treatment with 17β-estradiol prevented hyperphosphatemia and heart failure in female KL(−/−) mice. Mechanistically, treatment with 17β-estradiol rescued hyperphosphatemia via inhibiting renal Na-Pi co-transporter expression. Normalization of serum phosphorus levels by treatment with 17β-estradiol also abolished cardiac mitochondrial respiratory enzyme dysfunction, ROS overproduction, oxidative stress and cardiac cell apoptosis in female KL(−/−) mice.

Conclusion

Klotho deficiency causes acute heart failure via hyperphosphatemia in male mice which can be prevented by LPD. 17β-estradiol prevents Klotho deficiency-induced hyperphosphatemia and heart failure by eliminating upregulation of renal Na-Pi co-transporter expression in female mice.