Klotho's impact on diabetic nephropathy and its emerging connection to diabetic retinopathy

Vitamin D inhibits ferroptosis and mitigates the kidney injury of prediabetic mice by activating the Klotho/p53 signaling pathway

Diabetic nephropathy (DN) is a serious public health problem worldwide, and ferroptosis is deeply involved in the pathogenesis of DN. Prediabetes is a critical period in the prevention and control of diabetes and its complications, in which kidney injury occurs. This study aimed to explore whether ferroptosis would induce kidney injury in prediabetic mice, and whether vitamin D (VD) supplementation is capable of preventing kidney injury by inhibiting ferroptosis, while discussing the potential mechanisms. High-fat diet (HFD) fed KKAy mice and high glucose (HG) treated HK-2 cells were used as experimental subjects in the current study. Our results revealed that serious injury and ferroptosis take place in the kidney tissue of prediabetic mice; furthermore, VD intervention significantly improved the kidney structure and function in prediabetic mice and inhibited ferroptosis, showing ameliorated iron deposition, enhanced antioxidant capability, reduced reactive oxygen species (ROS) and lipid peroxidation accumulation. Meanwhile, VD up-regulated Klotho, solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) expression, and down-regulated p53, transferrin receptor 1 (TFR1) and Acyl-Coenzyme A synthetase long-chain family member 4 (ACSL4) expression. Moreover, we demonstrated that HG-induced ferroptosis is antagonized by treatment of VD and knockdown of Klotho attenuates the protective effect of VD on ferroptosis in vitro. In conclusion, ferroptosis occurs in the kidney of prediabetic mice and VD owns a protective effect on prediabetic kidney injury, possibly by via the Klotho/p53 pathway, thus inhibiting hyperglycemia-induced ferroptosis.

The mechanism and promising therapeutic strategy of diabetic cardiomyopathy dysfunctions: Focus on pyroptosis

Diabetes is a major risk factor for cardiovascular diseases, and myocardial damage caused by hyperglycemia is the main cause of heart failure. However, there is still a lack of systematic understanding of myocardial damage caused by diabetes. At present, we believe that the cellular inflammatory damage caused by hyperglycemia is one of the causes of diabetic cardiomyopathy. Pyroptosis, as a proinflammatory form of cell death, is closely related to the occurrence and development of diabetic cardiomyopathy. Therefore, this paper focuses on the important role of inflammation in the occurrence and development of diabetic cardiomyopathy. From the perspective of pyroptosis, we summarize the pyroptosis of different types of cells in diabetic cardiomyopathy and its related signaling pathways. It also summarizes the treatment of diabetic cardiomyopathy, hoping to provide methods for the prevention and treatment of diabetic cardiomyopathy by inhibiting pyroptosis.

α-Klotho prevents diabetic retinopathy by reversing the senescence of macrophages

BACKGROUND

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus (DM) and a significant cause of acquired blindness in the working-age population worldwide. Aging is considered as an important risk factor for DR development. Macrophages in aged mice bear typical M2 marker proteins but simultaneously express a pro-inflammatory factor profile. This may explain why the level of intraocular inflammation does not decrease during proliferative diabetic retinopathy (PDR) despite the occurrence of neovascularization and fibrosis (M2 activation). α-Klotho (KL) was originally discovered as a soluble anti-aging factor, which is mainly expressed in kidney tubular epithelium, choroid plexus in the brain and secreted in the blood. However, the role of KL in DR pathophysiology has not been previously reported.

METHODS

Type 1 (streptozotocin [STZ]-induced) and type 2 (a high-fat diet along with a low dose of STZ) diabetic mouse models were established and injected with or without KL adenovirus via the tail vein for 12 weeks. Vldlr-/- mice were injected intravitreally with or without soluble KL protein from P8 to P15. The retinal structure and function were analyzed by electroretinogram and optical coherence tomography. The neovascular lesions were analyzed by retinal flat mount and RPE flat mount. The senescence markers, macrophage morphology, and KL expression levels were detected by immunofluorescence staining. A cell model was constructed using RAW264.7 cells stimulated by 4-hydroxynonenal (4HNE) and transfected with or without KL adenovirus. The senescence-associated secretory phenotypes were detected by qRT-PCR. Senescence was detected by SA-β-Gal staining. Serum, aqueous humor, and vitreous humor KL levels of proliferative diabetic retinopathy (PDR) patients were measured by enzyme-linked immunosorbent assay. Quantitative proteomics and bioinformatics were applied to predict the change of proteins and biological function after overexpression of KL in macrophages. The effects of KL on the HECTD1 binding to IRS1 were analyzed by bioinformatics, molecular docking, and Western Blot.

RESULTS

Serum, aqueous humor, and vitreous humor KL levels were lower in patients with PDR than in those with cataracts. KL relieved the retinal structure damage, improved retina function, and inhibited retinal senescence in diabetic mice. KL administration attenuated the neovascular lesions in VLDLR-/- mice by decreasing the secretion of VEGFA and FGF2 from macrophages. KL also protected RAW264.7 cells from 4HNE-induced senescence. Additionally, it inhibited E3 ubiquitin ligase HECTD1 expression in both diabetic mouse peripheral blood mononuclear cells and 4HNE-treated RAW264.7 cells. KL inhibited HECTD1 binding to IRS1 and reduced the ubiquitination of IRS1.

CONCLUSIONS

Macrophage aging is involved in DM-induced retinopathy. KL alleviates DM-induced retinal macrophage senescence by downregulating HECTD1 and decreasing IRS1 ubiquitination and degradation. Meanwhile, KL administration attenuated the neovascular lesions by altering the activation state of macrophages and decreasing the expression of VEGFA and FGF2.

A PDE1 inhibitor, vinpocetine, ameliorates epithelial-mesenchymal transition and renal fibrosis in adenine-induced chronic kidney injury in rats by targeting the DNMT1/Klotho/β-catenin/Snail 1 and MMP-7 pathways

Tubulointerstitial fibrosis (TIF) is present with chronic kidney disease (CKD). Vinpocetine (Vinpo) is used for treating cerebrovascular deficits, exhibiting some kidney-beneficial effects; however, its role in TIF is uncertain. So, the aim of this study was to investigate its potential impact on adenine-induced fibrotic CKD and explore the underlying mechanistic aspects. Eighteen male Wistar rats were categorized into three groups (n = 6 each). Group I was kept as controls and given saline; group II received adenine (300 mg/kg, twice weekly, i.p.) for induction of the CKD model; and group III was administered Vinpo (20 mg/kg/d, orally) concurrently with adenine. All treatments were administered for 4 weeks. Vinpo revealed an improvement in renal function and an alleviation of inflammation triggered by adenine via diminishing serum tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6) levels. Further, Vinpo repressed the epithelial-mesenchymal transition (EMT) with preserved E-cadherin mRNA expression and lowered gene and immune expression of fibronectin and vimentin, respectively, besides attenuating the elevated G2/M arrest-related molecules (renal Ki67 protein contents and p21 gene expression). Renal pathological alterations caused by adenine were attenuated upon Vinpo administration. Interestingly, Vinpo suppressed abnormal renal β-catenin immunoreactivity, Snail 1, and MMP-7 gene expression while simultaneously restored Klotho protein expression by downregulating DNA methyltransferase 1 enzyme (DNMT1) protein expression in the kidney. These data indicated that Vinpo effectively mitigated EMT and G2/M arrest-induced renal fibrosis in adenine-induced CKD rats by targeting DNMT1-associated Klotho suppression, subsequently inhibiting β-catenin and its fibrotic downstream genes.

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.

Relationship between uric acid to high-density cholesterol ratio (UHR) and circulating α-klotho: evidence from NHANES 2007-2016

OBJECTIVE

To investigate the relationship between uric acid to high-density lipoprotein cholesterol ratio (UHR) and circulating α-klotho levels in U.S. adults.

METHODS

A cross-sectional study used data from the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2016. Circulating α-klotho was defined as the dependent variable and UHR was defined as the independent variable. Multivariable linear regression was performed to assess the relationship between the independent and dependent variables. The nonlinear relationship and effect size between UHR and α-klotho were evaluated using smooth curve fitting and threshold effect analysis. Subgroup analysis and sensitivity analysis were conducted to determine the stability of the results. The diagnostic performance of UHR and α-klotho in common elderly diseases was compared using ROC (Receiver Operating Characteristic) analysis.

RESULTS

Among 12,849 participants, there was a negative relationship between the UHR and circulating α-klotho. In the fully adjusted overall model, each unit increase in UHR was associated with a decrease of 4.1 pg/mL in α-klotho. The threshold effect analysis showed that before the inflection point of 8.2, each unit increase in UHR was associated with a decrease of 15.0 pg/mL in α-klotho; beyond the inflection point of 8.2, each unit increase in UHR was associated with a decrease of 2.8 pg/mL in α-klotho. Subgroup analyses and sensitivity analysis indicated that the relationship between UHR and α-klotho remained stable across most populations. The ROC diagnostic test indicated that the evaluative efficacy of UHR in diagnosing age-related diseases was comparable to that of α-klotho.

CONCLUSION

This study revealed that the UHR was associated with the circulating α-klotho concentration, with a negative association observed in most cases. This finding suggested that the UHR might be a promising indicator for evaluating circulating α-klotho levels.

Serum α-Klotho and fibroblast growth factor 23 levels are not associated with non-proliferative diabetic retinopathy in type 1 diabetes mellitus

Diabetic retinopathy is a commonly observed cause of blindness and is a common problem in individuals with diabetes. Recent investigations have showed the capability of serum α-Klotho and FGF 23 in mitigating the effects of diabetic retinopathy. This study aimed to discover the correlation between FGF 23, α-Klotho, and diabetic retinopathy in type 1 diabetics. This case-control study included 63 diabetic patients and 66 healthy controls. Following an overnight duration of fasting, morning blood samples were taken from both the patient and the control groups. The serum concentrations of α-Klotho and FGF 23 were quantified. An experienced ophthalmologist inspected the retinopathy. All participants in this study have moderate non-proliferative retinopathy. A p value under 0.05 was considered statistically significant. The mean α-Klotho level for retinopathic diabetic patients was 501.7 ± 172.2 pg/mL and 579.6 ± 312.1 pg/mL for non-retinopathic diabetic patients. In comparison, α-Klotho level of the control group was 523.2 ± 265.4 pg/mL (p = 0.531). The mean of FGF 23 level did not demonstrate a significant difference (p = 0.259). The mean FGF 23 level were 75.7 ± 14.0 pg/mL, 74.0 ± 14.8 pg/mL and 79.3 ± 14.4 pg/mL in groups, respectively. In conclusion, there was no significant difference in FGF 23 and α-Klotho levels between type 1 diabetics with and without retinopathy when compared to the control group.

Potential application of Klotho as a prognostic biomarker for patients with diabetic kidney disease: a meta-analysis of clinical studies

Background

Diabetic kidney disease (DKD) is a serious diabetic complication and the performance of serum Klotho in DKD's prognostic evaluation is controversial.

Objective

To assess the association of serum Klotho with adverse kidney and non-kidney clinical outcomes in patients with DKD.

Design

Clinical studies regarding the relationship of serum Klotho with DKD were included. Study quality was assessed using the Newcastle-Ottawa scale. Subgroup and sensitive analyses were performed to search for the source of heterogeneity.

Data sources and methods

We comprehensively searched PubMed, Embase, Web of Science, and Cochrane library databases up to 27 September 2022. The associations of Klotho with albuminuria, such as the urinary albumin creatinine ratio (UACR), kidney outcomes such as persistent albuminuria, estimated glomerular filtration rate decline, and non-kidney outcomes such as diabetic retinopathy, cardiovascular morbidity, and mortality, were evaluated. The indicators, such as the correlation coefficient (r), odds ratio (OR), relative risk, and hazard ratio, were retrieved or calculated from the eligible studies.

Results

In all, 17 studies involving 5682 participants fulfilled the inclusion criteria and were included in this meta-analysis. There was no significant association of serum Klotho with UACR in DKD patients [summary r, -0.28 (-0.55, 0.04)] with high heterogeneity. By contrast, a strong association was observed regarding serum Klotho with kidney outcomes [pooled OR, 1.60 (1.15, 2.23)], non-kidney outcomes [pooled OR, 2.78 (2.11, 3.66)], or combined kidney and non-kidney outcomes [pooled OR, 1.96 (1.45, 2.65)] with moderate heterogeneity. Subgroup analysis indicated that age, study design, and the estimated glomerular filtration rate may be the sources of heterogeneity.

Conclusion

A decreased serum Klotho level is possibly associated with an increased risk of developing kidney and non-kidney clinical outcomes in DKD patients; thus, Klotho may be a possible biomarker to predict DKD clinical outcomes. Additional studies are needed to clarify and validate Klotho's prognostic value.