α-Klotho is a non-enzymatic molecular scaffold for FGF23 hormone signalling

FGF-based drug discovery: advances and challenges

The fibroblast growth factor (FGF) family comprises 15 paracrine-acting and 3 endocrine-acting polypeptides, which govern a multitude of processes in human development, metabolism and tissue homeostasis. Therapeutic endocrine FGFs have recently advanced in clinical trials, with FGF19 and FGF21-based therapies on the cusp of approval for the treatment of primary sclerosing cholangitis and metabolic syndrome-associated steatohepatitis, respectively. By contrast, while paracrine FGFs were once thought to be promising drug candidates for wound healing, burns, tissue repair and ischaemic ailments based on their potent mitogenic and angiogenic properties, repeated failures in clinical trials have led to the widespread perception that the development of paracrine FGF-based drugs is not feasible. However, the observation that paracrine FGFs can exert FGF hormone-like metabolic activities has restored interest in these FGFs. The recent structural elucidation of the FGF cell surface signalling machinery and the formulation of a new threshold model for FGF signalling specificity have paved the way for therapeutically harnessing paracrine FGFs for the treatment of a range of metabolic diseases.

Dynamic single cell transcriptomics defines kidney FGF23/KL bioactivity and novel segment-specific inflammatory targets

Fibroblast growth factor 23 (FGF23) via its coreceptor αKlotho (KL) provides critical control of phosphate metabolism, which is altered in both rare and very common syndromes. However, the spatial-temporal mechanisms dictating kidney FGF23 functions remain poorly understood. Thus, developing approaches to modify specific FGF23-dictated pathways has proven problematic. Herein, wild type mice were injected with rFGF23 for one, four and 12h and kidney FGF23 bioactivity was determined at single cell resolution. Computational analysis identified distinct epithelial, endothelial, stromal, and immune cell clusters, with differential expressional analysis uniquely tracking FGF23 bioactivity at each time point. FGF23 actions were sex independent but critically relied upon constitutive KL expression mapped within proximal tubule (segments S1-S3) and distal convoluted tub/connecting tubule cell sub-populations. Temporal KL-dependent FGF23 responses drove unique and transient cellular identities, including genes in key MAPK-signaling and vitamin D-metabolic pathways via early- (transcription factor AP-1-related) and late-phase (initiation factor EIF2 signaling) transcriptional regulons. Combining ATACseq/RNAseq data from a cell line stably expressing KL with the in vivo scRNAseq pinpointed genomic accessibility changes in MAPK-dependent genes, including the identification of FGF23-dependent early growth factor-1 distal enhancers. Finally, we identified unexpected crosstalk between FGF23-mediated MAPK signaling and pro inflammatory TNF receptor activation via transcription factor NF-κB, which blocked FGF23 bioactivity in vitro and in vivo. Collectively, our findings have uncovered novel pathways at the single cell level that likely influence FGF23-dependent disease mechanisms.

HEBE: A novel chimeric chronokine for ameliorating memory deficits in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by amyloid-β and Tau protein depositions, with treatments focusing on single proteins have shown limited success due to the complexity of pathways involved. This study explored the potential of chronokines -proteins that modulate aging-related processes- as an alternative therapeutic approach. Specifically, we focused on a novel pleiotropic chimeric protein named HEBE, combining s-KL, sTREM2 and TIMP2, guided by bioinformatic analyses to ensure the preservation of each protein's conformation, crucial for their functions. In vitro studies confirmed HEBE's stability and enzymatic activities, even suggesting it has different activities compared to the individual chronokines. In vivo experiments on APP/Tau mice revealed improved learning and memory functions with HEBE treatment, along with decreased levels of phosphorylated Tau and minor effects on amyloid-β levels. These findings suggest that HEBE is as a promising therapeutic candidate for ameliorating memory deficits and reducing pTau in an AD mouse model.

Conformational landscape of soluble α-klotho revealed by cryogenic electron microscopy

α-Klotho (KLA) is a type-1 membranous protein that can associate with fibroblast growth factor receptor (FGFR) to form co-receptor for FGF23. The ectodomain of unassociated KLA is shed as soluble KLA (sKLA) to exert FGFR/FGF23-independent pleiotropic functions. The previously determined X-ray crystal structure of the extracellular region of sKLA in complex with FGF23 and FGFR1c suggests that sKLA functions solely as an on-demand coreceptor for FGF23. To understand the FGFR/FGF23-independent pleiotropic functions of sKLA, we investigated biophysical properties and structure of apo-sKLA. Single particle cryogenic electron microscopy (cryo-EM) revealed a 3.3 Å resolution structure of apo-sKLA that overlays well with its counterpart in the ternary complex with several distinct features. Compared to the ternary complex, the KL2 domain of apo-sKLA is more flexible. Three-dimensional variability analysis revealed that apo-sKLA adopts conformations with different KL1-KL2 interdomain bending and rotational angles. Mass photometry revealed that sKLA can form a stable structure with FGFR and/or FGF23 as well as sKLA dimer in solution. Cryo-EM supported the dimeric structure of sKLA. Recent studies revealed that FGF23 contains two KLA-binding sites. Our computational studies revealed that each site binds separate KLA in the dimer. The potential multiple forms and shapes of sKLA support its role as FGFR-independent hormone with pleiotropic functions. The ability of FGF23 to engage two KLA's simultaneously raises a potential new mechanism of action for FGF23-mediated signaling by the membranous klotho.

Pemigatinib suppresses liver fibrosis and subsequent osteodystrophy in mice

BACKGROUND

Liver fibrosis could lead to serious secondary diseases, including osteodystrophy. The interaction between liver and bone has not been fully elucidated, thus existing therapies for osteodystrophy secondary to liver fibrosis are often ineffective. FGF23 was initially found as an endocrine regulator of phosphate homeostasis, but recently, its involvement in fibrosis has been suggested. In this study, we hypothesized that the FGF23 level increases with liver injury, which in turn induces liver fibrosis and osteodystrophy.

METHODS

Liver fibrosis model mice were generated via carbon tetrachloride administration and bile duct ligation. Fibrosis was assessed using Masson trichrome staining and hydroxyproline assay. The bone structure was evaluated using dual-energy x-ray absorptiometry and microcomputed tomography. Human HSC lines LX-2 and primary rat HSCs were used for in vitro analyses.

RESULTS

Carbon tetrachloride-induced and bile duct ligation-induced liver injury increased the serum FGF23 level compared with that in control mice. RNA sequencing analysis of FGF23-treated LX-2 showed that FGF23 promotes the production of matrisome, which helps in forming the extracellular matrix. The FGF receptor antagonist pemigatinib alleviated carbon tetrachloride-induced and bile duct ligation-induced liver fibrosis and the deleterious alterations in bone density and microstructure in mice.

CONCLUSIONS

The serum FGF23 level increased with liver injury, and FGF23 promoted liver fibrosis. Moreover, pemigatinib alleviated liver fibrosis and hepatic osteodystrophy. These findings suggest that FGF23 mediates the communication between the liver and bone and that FGF23 may be a new therapeutic target for liver fibrosis and subsequent osteodystrophy.

The Complexity and Significance of Fibroblast Growth Factor (FGF) Signaling for FGF-Targeted Cancer Therapies

Fibroblast growth factors (FGFs) have diverse functions in the regulation of cell proliferation and differentiation in development, tissue maintenance, wound repair, and angiogenesis. The goal of this review paper is to (i) deliberate on the role of FGFs and FGF receptors (FGFRs) in different cancers, (ii) present advances in FGF-targeted cancer therapies, and (iii) explore cell signaling mechanisms that explain how FGF expression becomes dysregulated during cancer development. FGF is often mutated and overexpressed in cancer and the different FGF and FGFR isoforms have unique expression patterns and distinct roles in different cancers. Among the FGF members, the FGF 15/19 subfamily is particularly interesting because of its unique protein structure and role in endocrine function. The abnormal expression of FGFs in different cancer types (breast, colorectal, hepatobiliary, bronchogenic, and others) is examined and correlated with patient prognosis. The classification of FGF ligands based on their mode of action, whether autocrine, paracrine, endocrine, or intracrine, is illustrated, and an analysis of the binding specificity of FGFs to FGFRs is also provided. Moreover, the latest advances in cancer therapeutic strategies involving small molecules, ligand traps, and monoclonal antibody-based FGF inhibitors are presented. Lastly, we discuss how the dysregulation of FGF and FGFR expression affects FGF signaling and its role in cancer development.

Novel FGF21 analogues through structure-based optimization for therapeutic development

Fibroblast growth factor 21 (FGF21) plays a pivotal role in regulating metabolic processes and energy homeostasis, making it a promising therapeutic avenue for various obesity-related conditions. However, its therapeutic efficacy faces challenges due to its suboptimal pharmacokinetics and bioactivity. To overcome these limitations, we adapt a strategy in which key amino acid residues responsible for enhanced activity are pinpointed through sequence alignment and comparative analysis to develop long-acting FGF21 analogs. The mutant FGF21 analogs are fused with the Fc fragment. Here, we report the design, identification, and characterization of two distinct Fc-fused FGF21 analogs, Fc-FGF21(P119R) and Fc-FGF21(H125R), with significantly augmented potency. These findings hold promise for clinical applications, offering potential interventions for obesity-related metabolic disorders.

Phosphaturic mesenchymal tumor of the popliteal fossa: a case report and literature review

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by hypophosphatemia caused by excessive secretion of fibroblast growth factor-23 (FGF-23) by tumors. This leads to impaired bone mineralization and, ultimately, osteomalacia. The most common underlying cause is a phosphaturic mesenchymal tumor (PMT). Due to its rarity, nonspecific clinical presentation, and limited clinician awareness, TIO is frequently underdiagnosed or misdiagnosed. A 42-year-old man presented with persistent pain in the chest, lower back, knees, and ankles for more than six months, which had worsened in the preceding week. Laboratory tests revealed hypophosphatemia and abnormalities in markers of bone metabolism. Symptomatic treatment provided minimal improvement. The whole-body PET/CT scan subsequently identified a cystic and solid mass in the popliteal fossa of the right knee, with high somatostatin receptor expression. The tumor was surgically removed, and histopathological examination confirmed PMT. The patient's blood phosphorus concentration returned to normal one week after surgery, and levels of other laboratory indicators gradually returned to normal. Although symptoms persisted during the first postoperative week, significant relief was noted by the second week. This case report highlighted the necessity of improving clinical recognition and management of TIO to ensure timely diagnosis and treatment.

Decoding FGF/FGFR Signaling: Insights into Biological Functions and Disease Relevance

Fibroblast Growth Factors (FGFs) and their cognate receptors, FGFRs, play pivotal roles in a plethora of biological processes, including cell proliferation, differentiation, tissue repair, and metabolic homeostasis. This review provides a comprehensive overview of FGF-FGFR signaling pathways while highlighting their complex regulatory mechanisms and interconnections with other signaling networks. Further, we briefly discuss the FGFs involvement in developmental, metabolic, and housekeeping functions. By complementing current knowledge and emerging research, this review aims to enhance the understanding of FGF-FGFR-mediated signaling and its implications for health and disease, which will be crucial for therapeutic development against FGF-related pathological conditions.

Podocyte senescence: from molecular mechanisms to therapeutics

As an important component of the glomerular filtration membrane, the state of the podocytes is closely related to kidney function, they are also key cells involved in aging and play a central role in the damage caused by renal aging. Therefore, understanding the aging process of podocytes will allow us to understand their susceptibility to injury and identify targeted protective mechanisms. In fact, the process of physiological aging itself can induce podocyte senescence. Pathological stresses, such as oxidative stress, mitochondrial damage, secretion of senescence-associated secretory phenotype, reduced autophagy, oncogene activation, altered transcription factors, DNA damage response, and other factors, play a crucial role in inducing premature senescence and accelerating aging. Senescence-associated-β-galactosidase (SA-β-gal) is a marker of aging, and β-hydroxybutyric acid treatment can reduce SA-β-gal activity to alleviate cellular senescence and damage. In addition, CCAAT/enhancer-binding protein-α, transforming growth factor-β signaling, glycogen synthase kinase-3β, cycle-dependent kinase, programmed cell death protein 1, and plasminogen activator inhibitor-1 are closely related to aging. The absence or elevation of these factors can affect aging through different mechanisms. Podocyte injury is not an independent process, and injured podocytes interact with the surrounding epithelial cells or other kidney cells to mediate the injury or loss of podocytes. In this review, we discuss the manifestations, molecular mechanisms, biomarkers, and therapeutic drugs for podocyte senescence. We included elamipretide, lithium, calorie restriction, rapamycin; and emerging treatment strategies, such as gene and immune therapies. More importantly, we summarize how podocyte interact with other kidney cells.

The role of fibroblast growth factor 23 in regulation of phosphate balance

Phosphate is essential for numerous biological processes, and serum levels are tightly regulated to accomplish these functions. The regulation of serum phosphate in a narrow physiological range is a well-orchestrated process and involves the gastrointestinal (GI) tract, bone, kidneys, and several hormones, namely, parathyroid hormone, fibroblast growth factor 23 (FGF23), and 1,25-dihydroxyvitamin D (1,25 Vitamin D). Although primarily synthesized in the bone, FGF23, an endocrine FGF, acts on the kidney to regulate phosphate and Vitamin D homeostasis by causing phosphaturia and reduced levels of 1,25 Vitamin D. Recent studies have highlighted the complex regulation of FGF23 including transcriptional and post-translational modification and kidney-bone cross talk. Understanding FGF23 biology has led to the identification of novel therapeutic agents to treat diseases that disrupt phosphate metabolism secondary to FGF23. The focus of this review is to provide an overview of phosphate homeostasis, FGF23 biology, and the role of FGF23 in phosphate balance.

Systemic immunoinflammatory indexes in albuminuric adults are negatively associated with α-klotho: evidence from NHANES 2007-2016

BACKGROUND

Systemic Immune-Inflammation Index (SII) is a novel inflammatory biomarker closely associated with the inflammatory response and chronic kidney disease. Klotho is implicated as a pathogenic factor in the progression of kidney disease, and supplementation of Klotho may delay the progression of chronic kidney disease by inhibiting the inflammatory response. Our aim is to investigate the potential relationship between SII and Klotho in adult patients in the United States and explore the differences in the populations with and without albuminuria.

METHODS

We conducted a cross-sectional study recruiting adult participants with complete data on SII, Klotho, and urine albumin-to-creatinine ratio (ACR) from the National Health and Nutrition Examination Survey from 2007 to 2016. SII was calculated as platelet count × neutrophil count/lymphocyte count, with abnormal elevation defined as values exceeding 330 × 10^9/L. Albuminuria was defined as ACR >30 mg/g. Weighted multivariable regression analysis and subgroup analysis were employed to explore the independent relationship between SII and Klotho.

RESULTS

Our study included a total of 10,592 individuals. In all populations, non-albuminuria population, and proteinuria population with ACR ≥ 30, participants with abnormally elevated SII levels, as compared to those with SII less than 330 × 10^9/L, showed a negative correlation between elevated SII levels and increased Klotho, which persisted after adjusting for covariates.

CONCLUSIONS

There is a negative correlation between SII and Klotho in adult patients in the United States. This finding complements previous research but requires further analysis through large prospective studies.

Treating metabolic dysfunction-associated steatohepatitis: The fat-trimming FGF21 approach

Metabolic dysfunction-associated steatohepatitis (MASH) is a condition characterized by hepatosteatosis, inflammation, and tissue damage, with steatosis as the initial stage, which involves chronic, excess deposition of lipids in hepatic lipid droplets. Despite the growing prevalence and serious risks it poses, including liver decompensation, the need for transplantation, and increased patient mortality, MASH currently faces no approved pharmacotherapy. Several promising treatment candidates have emerged from recent clinical trials, including analogs of FGF21 and agonists of the associated FGFR1-KLB complex. These agents were well-tolerated in trials and have demonstrated significant improvements in both histological and biochemical markers of liver fat content, inflammation, injury, and fibrosis in patients with MASH. Endocrine FGF21 plays a vital role in maintaining homeostasis of lipid, glucose, and energy metabolism. It achieves this through pathways that target lipids or lipid droplets in adipocytes and hepatocytes. Mechanistically, pharmacological FGF21 acts as a potent catabolic factor to promote lipid or lipid droplet lipolysis, fatty acid oxidation, mitochondrial catabolic flux, and heat-dissipating energy expenditure, leading to effective clearance of hepatic and systemic gluco-lipotoxicity and inflammatory stress, thereby preventing obesity, diabetes, and MASH pathologies. In this review, we aim to provide an update on the outcomes of clinical trials for several FGF21 mimetics. We compare these outcomes with preclinical studies and offer a lipid-centric perspective on the mechanisms underlying the clinical benefits of these agents for MASH.

Overexpression of α-Klotho isoforms promotes distinct Effects on BDNF-Induced Alterations in Dendritic Morphology

α-Klotho (α-Kl) is a modulator of aging, neuroprotection, and cognition. Transcription of the Klotho gene produces two splice variants-a membrane protein (mKl), which can be cleaved and released into the extracellular milieu, and a truncated secreted form (sKl). Despite mounting evidence supporting a role for α-Kl in brain function, the specific roles of α-Kl isoforms in neuronal development remain elusive. Here, we examined α-Kl protein levels in rat brain and observed region-specific expression in the adult that differs between isoforms. In the developing hippocampus, levels of isoforms decrease after the third postnatal week, marking the end of the critical period for development. We overexpressed α-Kl isoforms in primary cultures of rat cortical neurons and evaluated effects on brain-derived neurotrophic factor (BDNF) signaling. Overexpression of either isoform attenuated BDNF-mediated signaling and reduced intracellular Ca2+ levels, with mKl promoting a greater effect. mKl or sKl overexpression in hippocampal neurons resulted in a partially overlapping reduction in secondary dendrite branching. Moreover, mKl overexpression increased primary dendrite number. BDNF treatment of neurons overexpressing sKl resulted in a dendrite branching phenotype similar to control neurons. In neurons overexpressing mKl, BDNF treatment restored branching of secondary and higher order dendrites close, but not distal, to the soma. Taken together, the data presented support the idea that sKl and mKl play distinct roles in neuronal development, and specifically, in dendrite morphogenesis.

Role of the intracerebroventricular injection α- klotho on food intake in broiler chicken: a novel study

This novel study investigated the effects of intracerebroventricular (ICV) injection α- klotho and its interaction with neuropeptide Y (NPY) receptors on food intake in broiler chicken. This study included 4 experiments with 4 groups in each with 11 replicates per group. Birds were feed deprived 3 h prior injection, following injection returned to their cage and food provided. In experiment 1, group 1 received ICV injection of the saline and groups 2 to 4 received ICV injection of the α-klotho (1, 2, and 4 µg), respectively. In experiment 2, chicken received ICV injection of the saline, B5063 (NPY1 receptor antagonist, 1.25 µg), α-klotho (4 µg) and co-injection of the B5063 + α-klotho. In experiments 3 and 4, SF22 (NPY2 receptor antagonist, 1.25 µg), and SML0891 (NPY5 receptor antagonist, 1.25 µg) were injected instead of the B5063. Then consumed food was measured at 30, 60, and 120 min post the injection. Based on results, ICV injection of the α-klotho (2 and 4 µg) significantly decreased food intake (P < 0.05). Co-injection of the B5063 + α-klotho significantly amplified hypophagic effect of the α-klotho (P < 0.05). α-klotho-induced hypophagia was not influenced by SF22 or SML0891. These results suggest that α-klotho-induced hypophagia is mediated via NPY1 receptors in broiler chicken.

Distinct role of Klotho in long bone and craniofacial bone: skeletal development, repair and regeneration

Bone defects are highly prevalent diseases caused by trauma, tumors, inflammation, congenital malformations and endocrine abnormalities. Ideally effective and side effect free approach to dealing with bone defects remains a clinical conundrum. Klotho is an important protein, which plays an essential role in regulating aging and mineral ion homeostasis. More recently, research revealed the function of Klotho in regulating skeleton development and regeneration. Klotho has been identified in mesenchymal stem cells, osteoblasts, osteocytes and osteoclasts in different skeleton regions. The specific function and regulatory mechanisms of Klotho in long bone and craniofacial bone vary due to their different embryonic development, ossification and cell types, which remain unclear and without conclusion. Moreover, studies have confirmed that Klotho is a multifunctional protein that can inhibit inflammation, resist cancer and regulate the endocrine system, which may further accentuate the potential of Klotho to be the ideal molecule in inducing bone restoration clinically. Besides, as an endogenous protein, Klotho has a promising potential for clinical therapy without side effects. In the current review, we summarized the specific function of Klotho in long bone and craniofacial skeleton from phenotype to cellular alternation and signaling pathway. Moreover, we illustrated the possible future clinical application for Klotho. Further research on Klotho might help to solve the existing clinical difficulties in bone healing and increase the life quality of patients with bone injury and the elderly.

Enhanced bioactivity and stability of a long-acting FGF21: A novel variant for the treatment of NASH

Fibroblast growth factor 21 (FGF21) is pivotal in regulating energy metabolism, highlighting substantial therapeutic potential for non-alcoholic steatohepatitis (NASH). Previously, we reported a long-acting FGF21 fusion protein, PsTag-FGF21, which was prepared by genetically fusing human FGF21 with a 648-residue polypeptide (PsTag). While this fusion protein demonstrated therapeutic efficacy against NASH, our final product analysis revealed the presence of fixed impurities resistant to effective removal, indicating potential degradation of PsTag-FGF21. Here, we enriched and analyzed the impurities, confirming our hypothesis regarding the C-terminal degradation of PsTag-FGF21. We now describe a new variant developed to eliminate the C-terminal degradation. By introducing one mutation located at the C-terminal of PsTag-FGF21(V169L), we demonstrated that the new molecule, PsTag-FGF21(V169L), exhibits many improved attributes. Compared with PsTag-FGF21, PsTag-FGF21(V169L) displayed elevated bioactivity and stability, along with a twofold enhanced binding affinity to the coreceptor β-Klotho. In vivo, the circulating half-life of PsTag-FGF21(V169L) was further enhanced compared with that of PsTag-FGF21. In NASH mice, PsTag-FGF21(V169L) demonstrated efficacy with sustained improvements in multiple metabolic parameters. Besides, PsTag-FGF21(V169L) demonstrated the ability to alleviate NASH by decreasing hepatocyte apoptosis. The superior biophysical, pharmacokinetic, and pharmacodynamic properties, along with the positive metabolic effects, imply that further clinical development of PsTag-FGF21(V169L) as a metabolic therapy for NASH patients may be warranted.

Exploring the Expression Profiles of Serum Inflammatory Proteins and Potential Antiaging Targets in Chinese Long-Living People

Chronic inflammation (inflammaging) is one of the important reasons for the development of age-related diseases and aging. Carrying out aging research and mining inflammatory markers can develop antiaging intervention targets, thus promoting healthy aging. By comparing the levels of inflammatory proteome in the serum of Chinese long-living people over 90 years and elderly aged 60∼79 which was detected by Olink platform, this study found that some pro-inflammatory or pro-aging proteins increased significantly in the long-living people, such as c-x-c motif chemokine ligand 9, accompanied by a significant increase in the levels of several anti-inflammatory or antiaging proteins, including fibroblast growth factor 19 and fibroblast growth factor 23, which confirmed that compared with elderly people, pro-inflammatory and anti-inflammatory (pro-aging and antiaging) tend to be balanced in long-living people, thus reducing the risk of age-related diseases and prolonging the lifespan of the elderly. These differently expressed proteins could serve as therapeutic targets and monitoring indicators for antiaging. At the same time, a few inflammatory protein markers, especially c-x-c motif chemokine ligand 9 and osteoprotegerin, could distinguish long-living and elderly correctly, which could be used to predict lifespan combined with other antiaging markers.

Lessons from Klotho mouse models to understand mineral homeostasis

AIM

Klotho, a key component of the endocrine fibroblast growth factor receptor-fibroblast growth factor axis, is a multi-functional protein that impacts renal electrolyte handling. The physiological significance of Klotho will be highlighted in the regulation of calcium, phosphate, and potassium metabolism.

METHODS

In this review, we compare several murine models with different renal targeted deletions of Klotho and the insights into the molecular and physiological function that these models offer.

RESULTS

In vivo, Klotho deficiency is associated with severely impaired mineral metabolism, with consequences on growth, longevity and disease development. Additionally, we explore the perspectives of Klotho in renal pathology and vascular events, as well as potential Klotho treatment options.

CONCLUSION

This comprehensive review emphasizes the use of Klotho to shed light on deciphering the renal molecular in vivo mechanisms in electrolyte handling, as well as novel therapeutic interventions.

Klotho enhances diastolic function in aged hearts through Sirt1-mediated pathways

Aging leads to a progressive decline in cardiac function, increasing the risk of heart failure with preserved ejection fraction (HFpEF). This study elucidates the impact of α-Klotho, an anti-aging hormone, on cardiac diastolic dysfunction and explore its downstream mechanisms. Aged wild-type and heterozygous Klotho-deficient mice received daily injection of soluble α-Klotho (sKL) for 10 weeks, followed by a comprehensive assessment of heart function by echocardiography, intracardiac pressure catheter, exercise tolerance, and cardiac pathology. Our findings show that klotho deficiency accentuated cardiac hypertrophy, diastolic dysfunction, and exercise intolerance, while sKL treatment ameliorates these abnormalities and improves cardiac capillary densities. Downstream of klotho, we focused on the Sirtuin1 (Sirt1) signaling pathway to elucidate the potential underlying mechanism by which Klotho improves diastolic function. We found that decreased Klotho levels were linked with Sirt1 deficiency, whereas sKL treatment restored Sirt1 expression in aged hearts and mitigated the DNA damage response pathway activation. Through tandem mass tag proteomics and unbiased acetylomics analysis, we identified 220 significantly hyperacetylated lysine sites in critical cardiac proteins of aged hearts. We found that sKL supplementation attenuated age-dependent DNA damage and cardiac diastolic dysfunction. In contrast, Klotho deficiency significantly increased hyperacetylation of several crucial cardiac contractile proteins, potentially impairing ventricular relaxation and diastolic function, thus predisposing to HFpEF. These results suggest the potential benefit of sKL supplementation as a promising therapeutic strategy for combating HFpEF in aging.

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.

New insights into the role of Klotho in inflammation and fibrosis: molecular and cellular mechanisms

As the body's defense mechanism against damage and infection, the inflammatory response is a pathological process that involves a range of inflammatory cells and cytokines. A healthy inflammatory response helps the body repair by eliminating dangerous irritants. However, tissue fibrosis can result from an overly intense or protracted inflammatory response. The anti-aging gene Klotho suppresses oxidation, delays aging, and fosters development of various organs. Numerous investigations conducted in the last few years have discovered that Klotho expression is changed in a variety of clinical diseases and is strongly linked to the course and outcome of a disease. Klotho functions as a co-receptor for FGF and as a humoral factor that mediates intracellular signaling pathways such as transforming growth factor β (TGF-β), toll-like receptors (TLRs), nuclear factor-kappaB (NF-κB), renin -angiotensin system (RAS), and mitogen-activated protein kinase (MAPK). It also interferes with the phenotype and function of inflammatory cells, such as monocytes, macrophages, T cells, and B cells. Additionally, it regulates the production of inflammatory factors. This article aims to examine Klotho's scientific advances in terms of tissue fibrosis and the inflammatory response in order to provide novel therapy concepts for fibrotic and inflammatory disorders.

Design, synthesis and antitumor activity of a novel FGFR2-selective degrader to overcome resistance of the FGFR2V564F gatekeeper mutation based on a pan-FGFR inhibitor

Aberrant activation of fibroblast growth factor receptors (FGFRs) contributes to the development and progression of multiple types of cancer. Although many FGFR inhibitors have been approved by the FDA, their long-term therapeutic efficacy is hampered by acquired resistance to gatekeeper mutations and low subtype selectivity. FGFR2 has been found to be frequently amplified or mutated in many tumors. In this study, we designed several PROTACs with different E3 ligands based on LY2874455. By screening the length of the linker and the binding site in various degraders, we obtained a novel and highly efficient FGFR2-selective degrader 28e (DC50 = 0.645 nM, DCmax = 86 %). Compound 28e selectively degraded FGFR2 and essentially avoided degradation of FGFR1,3,4 isoforms (DC50 > 300 nM). Compound 28e significantly inhibited the proliferation of FGFR2-overexpressing cell lines, including KATOIII, SNU16, and AN3CA (IC50 = 0.794 nM/0.207 nM/4.626 nM), comparable to parental inhibitors. At the same time, the preferred compound showed superiority over the parental inhibitor in kinase inhibitory activity against the gatekeeper mutant isoform FGFR2V564F (IC50 = 0.121 nM). In summary, we identified 28e as a novel selective degrader of FGFR2 with high potency and high potential to overcome resistance to gatekeeper mutation. The discovery of 28e provides new evidence for the strategy of pan-inhibitor-based development of selective degrading agents.

Exploring endocrine FGFs - structures, functions and biomedical applications

The family of fibroblast growth factors (FGFs) consists of 22 members with diverse biological functions in cells, from cellular development to metabolism. The family can be further categorized into three subgroups based on their three modes of action. FGF19, FGF21, and FGF23 are endocrine FGFs that act in a hormone-like/endocrine manner to regulate various metabolic activities. However, all three members of the endocrine family require both FGF receptors (FGFRs) and klotho co-receptors to elicit their functions. α-klotho and β-klotho act as scaffolds to bring endocrine FGFs closer to their receptors (FGFRs) to form active complexes. Numerous novel studies about metabolic FGFs' structures, mechanisms, and physiological insights have been published to further understand the complex molecular interactions and physiological activities of endocrine FGFs. Herein, we aim to review the structures, physiological functions, binding mechanisms to cognate receptors, and novel biomedical applications of endocrine FGFs in recent years.

Anti-Inflammatory Role of the Klotho Protein and Relevance to Aging

The α-Klotho protein (hereafter Klotho) is an obligate coreceptor for fibroblast growth factor 23 (FGF23). It is produced in the kidneys, brain and other sites. Klotho insufficiency causes hyperphosphatemia and other anomalies. Importantly, it is associated with chronic pathologies (often age-related) that have an inflammatory component. This includes atherosclerosis, diabetes and Alzheimer's disease. Its mode of action in these diseases is not well understood, but it inhibits or regulates multiple major pathways. Klotho has a membrane form and a soluble form (s-Klotho). Cytosolic Klotho is postulated but not well characterized. s-Klotho has endocrine properties that are incompletely elucidated. It binds to the FGF receptor 1c (FGFR1c) that is widely expressed (including endothelial cells). It also attaches to soluble FGF23, and FGF23/Klotho binds to FGFRs. Thus, s-Klotho might be a roaming FGF23 coreceptor, but it has other functions. Notably, Klotho (cell-bound or soluble) counteracts inflammation and appears to mitigate related aging (inflammaging). It inhibits NF-κB and the NLRP3 inflammasome. This inflammasome requires priming by NF-κB and produces active IL-1β, membrane pores and cell death (pyroptosis). In accord, Klotho countered inflammation and cell injury induced by toxins, damage-associated molecular patterns (DAMPs), cytokines, and reactive oxygen species (ROS). s-Klotho also blocks the TGF-β receptor and Wnt ligands, which lessens fibrotic disease. Low Klotho is associated with loss of muscle mass (sarcopenia), as occurs in aging and chronic diseases. s-Klotho counters the inhibitory effects of myostatin and TGF-β on muscle, reduces inflammation, and improves muscle repair following injury. The inhibition of TGF-β and other factors may also be protective in diabetic retinopathy and age-related macular degeneration (AMD). This review examines Klotho functions especially as related to inflammation and potential applications.

Analysis of Amyloid Fibrillation of Two Family 1 Glycoside Hydrolases

The formation and analysis of amyloid fibers by two β-glucosidases, BglA and BglB, belonging to the GH1 enzyme family, are reported. Both proteins have the (β/α)8 TIM-barrel fold, which is characteristic of this family and is also the most common protein structure. BglA is an octamer, whereas BglB is a monomer. Amyloid fibrillation using pH and temperature as perturbing agents was investigated using fluorescence spectroscopy as a preliminary approach and corroborated using wide-field optical microscopy, confocal microscopy, and field-emission scanning electron microscopy. These analyses showed that both enzymes fibrillate at a wide range of acidic and alkaline conditions and at several temperature conditions, particularly at acidic pH (3-4) and at temperatures between 45 and 65 °C. Circular dichroism spectroscopy corroborated the transition from an α-helix to a β-sheet secondary structure of both proteins in conditions where fibrillation was observed. Overall, our results suggest that fibrillation is a rather common phenomenon caused by protein misfolding, driven by a transition from an α-helix to a β-sheet secondary structure, that many proteins can undergo if subjected to conditions that disturb their native conformation.

Development of Zalfermin, a Long-Acting Proteolytically Stabilized FGF21 Analog

Here, we describe the development of the FGF21 analog zalfermin (NNC0194-0499, 15), intended for once-weekly sc dosing. Protein engineering was needed to address inherent druggability issues of the natural FGF21 hormone. Thus, deamidation of Asp121 was solved by mutation to glutamine, and oxidation of Met168 was solved by mutation to leucine. N-terminal region degradation by dipeptidyl peptidase IV was prevented by alanine residue elongation. To prevent inactivating metabolism by fibroblast activation protein and carboxypeptidase-like activity in the C-terminal region, and to achieve t1/2 extension (53 h in cynomolgus monkeys), we introduced a C18 fatty diacid at the penultimate position 180. The fatty diacid binds albumin in a reversible manner, such that the free fraction of zalfermin potently activates the FGF-receptor complex and retains receptor selectivity compared with FGF21, providing strong efficacy on body weight loss in diet-induced obese mice. Zalfermin is currently being clinically evaluated for the treatment of metabolic dysfunction-associated steatohepatitis.

Crosstalk between kidney and bone: insights from CKD-MBD

The kidneys play an important role in the regulation of phosphate and calcium balance and serum concentrations, coordinated by fibroblast growth factor 23 (FGF23), parathyroid hormone (PTH), and 1,25-dihydroxyvitamin D (1,25D). In patients with chronic kidney disease (CKD), this regulation is impaired, leading to CKD-mineral and bone disorder (CKD-MBD), characterized by decreased 1,25D, elevated FGF23, secondary hyperparathyroidism, hyperphosphatemia, bone abnormalities, and vascular and soft-tissue calcification. While bone abnormalities associated with CKD-MBD, known as renal osteodystrophy, have been recognized as the most typical interaction between the kidney and bone, a number of other kidney-bone interactions have been identified, for which our knowledge of the pathogenesis of CKD-MBD has played an important role. This article summarizes recent findings on CKD-MBD and explores the crosstalk between the kidney and bone from the perspective of CKD-MBD.

Glycosylation of FGF/FGFR: An underrated sweet code regulating cellular signaling programs

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute plasma-membrane localized signaling hubs that transmit signals from the extracellular environment to the cell interior, governing pivotal cellular processes like motility, metabolism, differentiation, division and death. FGF/FGFR signaling is critical for human body development and homeostasis; dysregulation of FGF/FGFR units is observed in numerous developmental diseases and in about 10% of human cancers. Glycosylation is a highly abundant posttranslational modification that is critical for physiological and pathological functions of the cell. Glycosylation is also very common within FGF/FGFR signaling hubs. Vast majority of FGFs (15 out of 22 members) are N-glycosylated and few FGFs are O-glycosylated. Glycosylation is even more abundant within FGFRs; all FGFRs are heavily N-glycosylated in numerous positions within their extracellular domains. A growing number of studies points on the multiple roles of glycosylation in fine-tuning FGF/FGFR signaling. Glycosylation modifies secretion of FGFs, determines their stability and affects interaction with FGFRs and co-receptors. Glycosylation of FGFRs determines their intracellular sorting, constitutes autoinhibitory mechanism within FGFRs and adjusts FGF and co-receptor recognition. Sugar chains attached to FGFs and FGFRs constitute also a form of code that is differentially decrypted by extracellular lectins, galectins, which transform FGF/FGFR signaling at multiple levels. This review focuses on the identified functions of glycosylation within FGFs and FGFRs and discusses their relevance for the cell physiology in health and disease.

Tumor-induced osteomalacia

Tumor-induced osteomalacia is one of paraneoplastic syndromes characterized by hypophosphatemia caused by excessive actions of fibroblast growth factor 23 (FGF23). Since the cloning of FGF23 about 20 years ago, more widespread awareness of this disease has been achieved. However, there still remain several difficulties in the management of patients with this disease. In this review, these clinical problems are discussed together with the physiological and pathophysiological functions of FGF23. Personal proposals in the management of patients with suspected patients with tumor-induced osteomalacia are also presented.

Hypericin Alleviates Chronic Kidney Disease-induced Left Ventricular Hypertrophy by Regulation of FGF23-FGFR4 Signaling Pathway

ABSTRACT

Chronic kidney disease (CKD) is a significant global health threat that imposes a substantial burden on both individuals and societies. CKD frequently correlates with cardiovascular events, particularly left ventricular hypertrophy (LVH), which contributes to the high mortality rate associated with CKD. Fibroblast growth factor 23 (FGF23), a hormone primarily involved in regulating calcium and phosphorus metabolism, has been identified as a major risk factor for LVH in CKD patients. Elevated serum FGF23 levels are known to induce LVH and myocardial fibrosis by activating the fibroblast growth factor receptor 4 (FGFR4) signal pathway. Therefore, targeting FGFR4 and its downstream signaling pathways holds potential as a treatment strategy for cardiac dysfunction in CKD. In our current study, we have discovered that Hypericin, a key component derived from Hypericum perforatum , has the ability to alleviate CKD-related LVH by targeting the FGFR4/phospholipase C gamma 1 (PLCγ1) signaling pathway. Through in vitro experiments using rat cardiac myocyte H9c2 cells, we observed that Hypericin effectively inhibits FGF23-induced hypertrophy and fibrosis by suppressing the FGFR4/PLCγ1/calcineurin/nuclear factor of activated T-cell (NFAT3) signaling pathway. In addition, our in vivo studies using mice on a high-phosphate diet and rat models of 5/6 nephrectomy demonstrated that Hypericin has therapeutic effects against CKD-induced LVH by modulating the FGFR4/PLCγ1/calcineurin/NFAT3 signaling pathway. In conclusion, our research highlights the potential of Hypericin as a candidate for the treatment of CKD-induced cardiomyopathy. By suppressing the FGFR4/PLCγ1 signaling pathway, Hypericin shows promise in attenuating LVH and myocardial fibrosis associated with CKD.

Dynamic Single Cell Transcriptomics Defines Kidney FGF23/KL Bioactivity and Novel Segment-Specific Inflammatory Targets

FGF23 via its coreceptor αKlotho (KL) provides critical control of phosphate metabolism, which is altered in rare and very common syndromes, however the spatial-temporal mechanisms dictating renal FGF23 functions remain poorly understood. Thus, developing approaches to modify specific FGF23-dictated pathways has proven problematic. Herein, wild type mice were injected with rFGF23 for 1, 4 and 12h and renal FGF23 bioactivity was determined at single cell resolution. Computational analysis identified distinct epithelial, endothelial, stromal, and immune cell clusters, with differential expressional analysis uniquely tracking FGF23 bioactivity at each time point. FGF23 actions were sex independent but critically relied upon constitutive KL expression mapped within proximal tubule (S1-S3) and distal tubule (DCT/CNT) cell sub-populations. Temporal KL-dependent FGF23 responses drove unique and transient cellular identities, including genes in key MAPK- and vitamin D-metabolic pathways via early- (AP-1-related) and late-phase (EIF2 signaling) transcriptional regulons. Combining ATACseq/RNAseq data from a cell line stably expressing KL with the in vivo scRNAseq pinpointed genomic accessibility changes in MAPK-dependent genes, including the identification of FGF23-dependent EGR1 distal enhancers. Finally, we isolated unexpected crosstalk between FGF23-mediated MAPK signaling and pro-inflammatory TNF receptor activation via NF-κB, which blocked FGF23 bioactivity in vitro and in vivo . Collectively, our findings have uncovered novel pathways at the single cell level that likely influence FGF23-dependent disease mechanisms.

Translational statement

Inflammation and elevated FGF23 in chronic kidney disease (CKD) are both associated with poor patient outcomes and mortality. However, the links between these manifestations and the effects of inflammation on FGF23-mediated mineral metabolism within specific nephron segments remain unclear. Herein, we isolated an inflammatory pathway driven by TNF/NF-κB associated with regulating FGF23 bioactivity. The findings from this study could be important in designing future therapeutic approaches for chronic mineral diseases, including potential combination therapies or early intervention strategies. We also suggest that further studies could explore these pathways at the single cell level in CKD models, as well as test translation of our findings to interactions of chronic inflammation and elevated FGF23 in human CKD kidney datasets.

The Intricacies of Renal Phosphate Reabsorption-An Overview

To maintain an optimal body content of phosphorus throughout postnatal life, variable phosphate absorption from food must be finely matched with urinary excretion. This amazing feat is accomplished through synchronised phosphate transport by myriads of ciliated cells lining the renal proximal tubules. These respond in real time to changes in phosphate and composition of the renal filtrate and to hormonal instructions. How they do this has stimulated decades of research. New analytical techniques, coupled with incredible advances in computer technology, have opened new avenues for investigation at a sub-cellular level. There has been a surge of research into different aspects of the process. These have verified long-held beliefs and are also dramatically extending our vision of the intense, integrated, intracellular activity which mediates phosphate absorption. Already, some have indicated new approaches for pharmacological intervention to regulate phosphate in common conditions, including chronic renal failure and osteoporosis, as well as rare inherited biochemical disorders. It is a rapidly evolving field. The aim here is to provide an overview of our current knowledge, to show where it is leading, and where there are uncertainties. Hopefully, this will raise questions and stimulate new ideas for further research.

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.

Development of an α-Klotho Recognizing High-Affinity Peptide Probe from In-Solution Enrichment

The kidney, parathyroid gland, and choroid plexus express the aging-related transmembrane protein α-Klotho, a coreceptor of the fibroblast growth factor 23 (FGF23) receptor complex. Reduced α-Klotho levels are correlated with chronic kidney disease and other age-related diseases, wherein they are released from membranes into circulation. Klotho's potential physiological action as a hormone is of current scientific interest. Part of the challenges associated with advancing these studies, however, has been the long-standing difficulty in detecting soluble α-Klotho in biofluids. Here, we describe the discovery of peptides that recognize α-Klotho with high affinity and selectivity by applying in-solution size-exclusion-based affinity selection-mass spectrometry (AS-MS). After two rounds of AS-MS and subsequent N-terminal modifications, the peptides improved their binding affinity to α-Klotho by approximately 2300-fold compared to the reported starting peptide Pep-10, previously designed based on the C-terminal region of FGF23. The lead peptide binders were shown to enrich α-Klotho from cell lysates and to label α-Klotho in kidney cells. Our results further support the utility of in-solution, label-free AS-MS protocols to discover peptide-based binders to target proteins of interest with high affinity and selectivity, resulting in functional probes for biological studies.

Relationships of serum FGF23 and α-klotho with atherosclerosis in patients with type 2 diabetes mellitus

BACKGROUND

Compelling evidence suggests that calcium/phosphorus homeostasis-related parameters may be linked to diabetes mellitus and cardiovascular events. However, few studies have investigated the association of fibroblast growth factor 23 (FGF23), α-klotho and FGF23/α-klotho ratio with atherosclerosis in patients with type 2 diabetes mellitus (T2DM).

OBJECTIVE

This study was designed to evaluate whether FGF23, α-klotho and FGF23/α-klotho ratio are associated with T2DM and further to explore the relationships between these three factors and atherosclerosis in Chinese patients with T2DM.

METHODS

Serum FGF23 and α-klotho levels were measured via an enzyme-linked immunosorbent assay (ELISA) kit, and the carotid intima-media thickness (CIMT) was assessed via high-resolution color Doppler ultrasonography. The associations of serum FGF23, α-klotho and FGF23/α-klotho ratio with atherosclerosis in T2DM patients were evaluated using multivariable logistic regression models.

RESULTS

This cross-sectional study involved 403 subjects (207 with T2DM and 196 without T2DM), 41.7% of the patients had atherosclerosis, and 67.2% of the carotid intima were thickened to a thickness greater than 0.9 mm. Compared with those in the lowest tertile, higher tertiles of FGF23 levels and FGF23/α-klotho ratio were positively associated with T2DM after adjusting for covariates, and serum α-klotho concentration was inversely correlated with T2DM (all P values < 0.01). Moreover, elevated serum FGF23 levels and FGF23/α-klotho ratio were positively associated with CIMT and carotid atherosclerosis in T2DM patients (all P values < 0.01). Further spline analysis similarly revealed linear dose‒response relationship (all P values < 0.01). And there was still significant differences in CIMT and carotid atherosclerosis between the highest group of α-klotho and the reference group in T2DM patients (P values = 0.05).

CONCLUSIONS

T2DM was positively linearly related to serum FGF23 concentration and FGF23/α-klotho ratio, and negatively correlated with serum α-klotho concentration. Furthermore, both FGF23 and FGF23/α-klotho ratio were positively correlated with CIMT and atherosclerosis in T2DM patients, while α-klotho was inversely correlated with both CIMT and atherosclerosis, although the associations were not completely significant. Prospective exploration and potential mechanisms underlying these associations remain to be further elucidated.

Serum klotho levels and mortality patterns in frail individuals: unraveling the u-shaped association

BACKGROUND

Frailty, a clinical syndrome intricately linked with the aging process, stands as a harbinger of numerous adverse outcomes, most notably mortality. This study aimed to elucidate the association between serum α-klotho concentration and mortality patterns, including all-cause and cause-specific mortality, in patients with frailty.

METHODS

The study employed Cox proportional hazard models, smoothed curve fitting, and supplementary analyses, encompassing threshold effect analysis, subgroup and sensitivity analyses, to explore the relationship between α-klotho levels and mortality, including all-cause, CVD, and cancer-related mortality.

RESULTS

Among the 2,608 frail individuals (mean age: 60.78 [SD 10.48] years; 59.89% female), the mortality stood at 25.35% during a median follow-up period of 6.95 years. Both unadjusted and adjusted models revealed a significant inverse association between higher serum α-klotho levels and the risk of all-cause and CVD-related mortality ([mean(95% CI) 0.68 (0.55, 0.83)] for all-cause mortality; [mean(95% CI) 0.48 (0.32, 0.74)] for CVD-related mortality, all P for trend < 0.001). Notably, log2-klotho displayed a U-shaped correlation with all-cause mortality and cancer mortality, characterized by thresholds of 9.48 and 9.55, respectively. The robustness of these findings was consistently supported by subgroup and sensitivity analyses.

CONCLUSION

This study unveils a U shaped association between serum α-klotho levels and both all-cause and cancer-related mortality among middle-aged and elderly individuals with frailty in the United States. The identified serum α-klotho thresholds, at 714.8 pg/ml for all-cause mortality and 750.6 pg/ml for cancer-related mortality, hold promise as potential targets for interventions aimed at mitigating the risks of premature death and cancer within this vulnerable population.

Regulation of FGF23 Production in Osteocytes

PURPOSE OF REVIEW

FGF23 is a bone-derived hormone working to reduce serum phosphate level. This review focuses on recent findings regarding regulatory mechanisms of FGF23 expression in osteocytes, FGF23 levels, and activities.

RECENT FINDINGS

Circulatory FGF23 levels reflecting FGF23 biological activities can be regulated by both FGF23 expression and posttranslational modification of FGF23 protein. O-linked glycosylation and phosphorylation of FGF23 protein as well as enzymes that can cleave FGF23 protein are involved in the posttranslational modification. However, precise mechanisms of FGF23 protein processing are not clear. Several extracellular factors have been shown to affect FGF23 levels in kidney injuries. Contribution of these factors may be different depending on the causes and stages of kidney injury. FGF23 activities are regulated by complex mechanisms involving transcriptional and posttranslational modulations. There still remain several questions regarding the regulatory mechanisms of FGF23 expression and FGF23 processing.

C-terminal fragment of fibroblast growth factor 23 improves heart function in murine models of high intact fibroblast growth factor 23

Cardiovascular disease (CVD) is the major cause of death in chronic kidney disease (CKD) and is associated with high circulating fibroblast growth factor (FGF)23 levels. It is unresolved whether high circulating FGF23 is a mere biomarker or pathogenically contributes to cardiomyopathy. It is also unknown whether the C-terminal FGF23 peptide (cFGF23), a natural FGF23 antagonist proteolyzed from intact FGF23 (iFGF23), retards CKD progression and improves cardiomyopathy. We addressed these questions in three murine models with high endogenous FGF23 and cardiomyopathy. First, we examined wild-type (WT) mice with CKD induced by unilateral ischemia-reperfusion and contralateral nephrectomy followed by a high-phosphate diet. These mice were continuously treated with intraperitoneal implanted osmotic minipumps containing either iFGF23 protein to further escalate FGF23 bioactivity, cFGF23 peptide to block FGF23 signaling, vehicle, or scrambled peptide as negative controls. Exogenous iFGF23 protein given to CKD mice exacerbated pathological cardiac remodeling and CKD progression, whereas cFGF23 treatment improved heart and kidney function, attenuated fibrosis, and increased circulating soluble Klotho. WT mice without renal insult placed on a high-phosphate diet and homozygous Klotho hypomorphic mice, both of whom develop moderate CKD and clear cardiomyopathy, were treated with cFGF23 or vehicle. Mice treated with cFGF23 in both models had improved heart and kidney function and histopathology. Taken together, these data indicate high endogenous iFGF23 is not just a mere biomarker but pathogenically deleterious in CKD and cardiomyopathy. Furthermore, attenuation of FGF23 bioactivity by cFGF23 peptide is a promising therapeutic strategy to protect the kidney and heart from high FGF23 activity.NEW & NOTEWORTHY There is a strong correlation between cardiovascular morbidity and high circulating fibroblast growth factor 23 (FGF23) levels, but causality was never proven. We used a murine chronic kidney disease (CKD) model to show that intact FGF23 (iFGF23) is pathogenic and contributes to both CKD progression and cardiomyopathy. Blockade of FGF23 signaling with a natural proteolytic product of iFGF23, C-terminal FGF23, alleviated kidney and cardiac histology, and function in three separate murine models of high endogenous FGF23.

Conformational landscape of soluble α-klotho revealed by cryogenic electron microscopy

α-Klotho (KLA) is a type-1 membranous protein that can associate with fibroblast growth factor receptor (FGFR) to form co-receptor for FGF23. The ectodomain of unassociated KLA is shed as soluble KLA (sKLA) to exert FGFR/FGF23-independent pleiotropic functions. The previously determined X-ray crystal structure of the extracellular region of sKLA in complex with FGF23 and FGFR1c suggests that sKLA functions solely as an on-demand coreceptor for FGF23. To understand the FGFR/FGF23-independent pleiotropic functions of sKLA, we investigated biophysical properties and structure of apo-sKLA. Mass photometry revealed that sKLA can form a stable structure with FGFR and/or FGF23 as well as sKLA dimer in solution. Single particle cryogenic electron microscopy (cryo-EM) supported the dimeric structure of sKLA. Cryo-EM further revealed a 3.3Å resolution structure of apo-sKLA that overlays well with its counterpart in the ternary complex with several distinct features. Compared to the ternary complex, the KL2 domain of apo-sKLA is more flexible. 3D variability analysis revealed that apo-sKLA adopts conformations with different KL1-KL2 interdomain bending and rotational angles. The potential multiple forms and shapes of sKLA support its role as FGFR-independent hormone with pleiotropic functions. A comprehensive understanding of the sKLA conformational landscape will provide the foundation for developing klotho-related therapies for diseases.

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.

Therapeutic potential of AAV-FL-Klotho in obesity: Impact on weight loss and lipid metabolism in mice

Klotho, an anti-aging protein, has gained attention for its protective effects against various diseases, including metabolic disorders, through recombinant Klotho administration. However, the potential of Klotho as a target for gene therapy requires further exploration, as it remains relatively understudied in the context of metabolic disorders. In this study, we demonstrate that AAV-full length(FL)-Klotho administration induces weight loss in mice and provides protection against high-fat diet (HFD)-induced obesity and hepatic steatosis, concurrently reducing the weights of white adipose tissue and liver. AAV-FL-Klotho administration also enhanced thermogenic gene expression in brown adipose tissue (BAT) and improved the morphology of interscapular BAT. The weight loss effect of AAV-FL-Klotho was found to be, at least in part, mediated by UCP1-dependent thermogenesis in brown adipocytes, potentially influenced by hepatokines secreted from AAV-FL-Klotho-transduced hepatocytes. These findings suggest that AAV-FL-Klotho is an attractive candidate for gene therapy to combat obesity. Nevertheless, unbiased experiments have also revealed disturbances in lipid metabolism due to AAV-FL-Klotho, as evidenced by the emergence of lipomas and increased expression of hepatic lipogenic proteins.

Bibliometric study and review of Klotho research: global characteristics and trends from 2000 to 2023

BACKGROUND

Although Klotho-related research has seen a significant upsurge, the field lacks comprehensive analytical representation and in-depth exploration of pertinent areas such as prevailing research trends and key focus areas.

METHOD

This review presents a bibliometric analysis of literature data gathered from the Web of Science Core Collection databases from January 1, 2000, to April 30, 2023. Parameters such as co-authorship, co-citation, co-occurrence, and the emergence of publications, countries, categories, references, and keywords were scrutinized predominantly using Citespace software.

RESULTS

Our investigation amassed a total of 3548 papers, with the United States leading in the quantity of publications (1175, accounting for 33.12%), followed by China (867, representing 24.44%), and Japan (439, accounting for 12.37%). While the United States is preeminent in the overall volume of publications, Scotland holds prominence in terms of centrality. Out of a total of 96 subject categories, urology and nephrology (573), and endocrinology and metabolism (542) were the two leading domains of Klotho-related publications. The 2011 paper titled "FGF23 induces left ventricular hypertrophy" by Faul C et al. holds the distinction of being the most frequently cited. The keywords "fibroblast growth factor 23," "phosphate homeostasis," and "functional variants" demonstrated the highest intensity, underscoring the potential of these research areas.

CONCLUSION

As the volume of literature grows, the role of Klotho in disease management and its applicability as a marker in disease progression warrant vigilant tracking and study.

Phosphate in Cardiovascular Disease: From New Insights Into Molecular Mechanisms to Clinical Implications

Hyperphosphatemia is a common feature in patients with impaired kidney function and is associated with increased risk of cardiovascular disease. This phenomenon extends to the general population, whereby elevations of serum phosphate within the normal range increase risk; however, the mechanism by which this occurs is multifaceted, and many aspects are poorly understood. Less than 1% of total body phosphate is found in the circulation and extracellular space, and its regulation involves multiple organ cross talk and hormones to coordinate absorption from the small intestine and excretion by the kidneys. For phosphate to be regulated, it must be sensed. While mostly enigmatic, various phosphate sensors have been elucidated in recent years. Phosphate in the circulation can be buffered, either through regulated exchange between extracellular and cellular spaces or through chelation by circulating proteins (ie, fetuin-A) to form calciprotein particles, which in themselves serve a function for bulk mineral transport and signaling. Either through direct signaling or through mediators like hormones, calciprotein particles, or calcifying extracellular vesicles, phosphate can induce various cardiovascular disease pathologies: most notably, ectopic cardiovascular calcification but also left ventricular hypertrophy, as well as bone and kidney diseases, which then propagate phosphate dysregulation further. Therapies targeting phosphate have mostly focused on intestinal binding, of which appreciation and understanding of paracellular transport has greatly advanced the field. However, pharmacotherapies that target cardiovascular consequences of phosphate directly, such as vascular calcification, are still an area of great unmet medical need.

Targeting the FGF19-FGFR4 pathway for cholestatic, metabolic, and cancerous diseases

Human fibroblast growth factor 19 (FGF19, or FGF15 in rodents) plays a central role in controlling bile acid (BA) synthesis through a negative feedback mechanism. This process involves a postprandial crosstalk between the BA-activated ileal farnesoid X receptor and the hepatic Klotho beta (KLB) coreceptor complexed with fibrobalst growth factor receptor 4 (FGFR4) kinase. Additionally, FGF19 regulates glucose, lipid, and energy metabolism by coordinating responses from functional KLB and FGFR1-3 receptor complexes on the periphery. Pharmacologically, native FGF19 or its analogs decrease elevated BA levels, fat content, and collateral tissue damage. This makes them effective in treating both cholestatic diseases such as primary biliary or sclerosing cholangitis (PBC or PSC) and metabolic abnormalities such as nonalcoholic steatohepatitis (NASH). However, chronic administration of FGF19 drives oncogenesis in mice by activating the FGFR4-dependent mitogenic or hepatic regenerative pathway, which could be a concern in humans. Agents that block FGF19 or FGFR4 signaling have shown great potency in preventing FGF19-responsive hepatocellular carcinoma (HCC) development in animal models. Recent phase 1/2 clinical trials have demonstrated promising results for several FGF19-based agents in selectively treating patients with PBC, PSC, NASH, or HCC. This review aims to provide an update on the clinical development of both analogs and antagonists targeting the FGF19-FGFR4 signaling pathway for patients with cholestatic, metabolic, and cancer diseases. We will also analyze potential safety and mechanistic concerns that should guide future research and advanced trials.

Association Between Serum Klotho and Chronic Obstructive Pulmonary Disease in US Middle-Aged and Older Individuals: A Cross-Sectional Study from NHANES 2013-2016

Purpose

This study sought to examine the potential association between serum Klotho levels and the prevalence of COPD in the United States.

Patients and Methods

This study was a cross-sectional analysis involving 4361 adults aged 40-79 years participating in the US National Health and Nutrition Examination Survey (NHANES) conducted between 2013 and 2016. Our investigation utilized multivariate logistic regression and restricted cubic spline (RCS) regression to explore the potential correlation between serum Klotho concentrations and the prevalence of COPD. Additionally, we conducted stratified and interaction analyses to evaluate the consistency and potential modifiers of this relationship.

Results

In this study encompassing 4631 patients (with an average age of 57.6 years, 47.5% of whom were male), 445 individuals (10.2%) were identified as having COPD. In the fully adjusted model, ln-transformed serum Klotho was negatively associated with COPD (OR = 0.71; 95% CI: 0.51-0.99; p = 0.043). Meanwhile, compared with quartile 1, serum Klotho levels in quartiles 2-4 yielded odds ratios (ORs) (95% CI) for COPD were 0.84 (0.63~1.11), 0.76 (0.56~1.02), 0.84 (0.62~1.13), respectively. A negative relationship was observed between the ln-transformed serum Klotho and occurrence of COPD (nonlinear: p = 0.140). the association between ln-transformed serum Klotho and COPD were stable in stratified analyses.

Conclusion

Serum Klotho was negatively associated with the incidence of COPD, when ln-transformed Klotho concentration increased by 1 unit, the risk of COPD was 29% lower.

The Bone-Vascular Axis in Chronic Kidney Disease: From Pathophysiology to Treatment

PURPOSE OF REVIEW

This review aims to describe the pathogenic factors involved in bone-vessel anomalies in CKD which are the object of numerous experimental and clinical research.

RECENT FINDINGS

Knowledge on the pathophysiological mechanisms involved in the regulation of vascular calcification and mineral-bone disorders is evolving. Specific bone turnover anomalies influence the vascular health while recent studies demonstrate that factors released by the calcified vessels also contribute to bone deterioration in CKD. Current therapies used to control mineral dysregulations will impact both the vessels and bone metabolism. Available anti-osteoporotic treatments used in non-CKD population may negatively or positively affect vascular health in the context of CKD. It is essential to study the bone effects of the new therapeutic options that are currently under investigation to reduce vascular calcification. Our paper highlights the complexity of the bone-vascular axis and discusses how current therapies may affect both organs in CKD.

The basics of phosphate metabolism

Phosphorus is an essential mineral that is, in the form of inorganic phosphate (Pi), required for building cell membranes, DNA and RNA molecules, energy metabolism, signal transduction and pH buffering. In bone, Pi is essential for bone stability in the form of apatite. Intestinal absorption of dietary Pi depends on its bioavailability and has two distinct modes of active transcellular and passive paracellular absorption. Active transport is transporter mediated and partly regulated, while passive absorption depends mostly on bioavailability. Renal excretion controls systemic Pi levels, depends on transporters in the proximal tubule and is highly regulated. Deposition and release of Pi into and from soft tissues and bone has to be tightly controlled. The endocrine network coordinating intestinal absorption, renal excretion and bone turnover integrates dietary intake and metabolic requirements with renal excretion and is critical for bone stability and cardiovascular health during states of hypophosphataemia or hyperphosphataemia as evident from inborn or acquired diseases. This review provides an integrated overview of the biology of phosphate and Pi in mammals.

Endocrine FGFs and their signaling in the brain: Relevance for energy homeostasis

Since their discovery in 2000, there has been a continuous expansion of studies investigating the physiology, biochemistry, and pharmacology of endocrine fibroblast growth factors (FGFs). FGF19, FGF21, and FGF23 comprise a subfamily with attributes that distinguish them from typical FGFs, as they can act as hormones and are, therefore, referred to as endocrine FGFs. As they participate in a broad cross-organ endocrine signaling axis, endocrine FGFs are crucial lipidic, glycemic, and energetic metabolism regulators during energy availability fluctuations. They function as powerful metabolic signals in physiological responses induced by metabolic diseases, like type 2 diabetes and obesity. Pharmacologically, FGF19 and FGF21 cause body weight loss and ameliorate glucose homeostasis and energy expenditure in rodents and humans. In contrast, FGF23 expression in mice and humans has been linked with insulin resistance and obesity. Here, we discuss emerging concepts in endocrine FGF signaling in the brain and critically assess their putative role as therapeutic targets for treating metabolic disorders.