Regulation of α-Klotho Expression by Dietary Phosphate During Growth Periods

Underlying Mechanisms and Treatment of Cellular Senescence-Induced Biological Barrier Interruption and Related Diseases

Given its increasing prevalence, aging is of great concern to researchers worldwide. Cellular senescence is a physiological or pathological cellular state caused by aging and a prominent risk factor for the interruption of the integrity and functionality of human biological barriers. Health barriers play an important role in maintaining microenvironmental homeostasis within the body. The senescence of barrier cells leads to barrier dysfunction and age-related diseases. Cellular senescence has been reported to be a key target for the prevention of age-related barrier diseases, including Alzheimer's disease, Parkinson's disease, age-related macular degeneration, diabetic retinopathy, and preeclampsia. Drugs such as metformin, dasatinib, quercetin, BCL-2 inhibitors, and rapamycin have been shown to intervene in cellular senescence and age-related diseases. In this review, we conclude that cellular senescence is involved in age-related biological barrier impairment. We further outline the cellular pathways and mechanisms underlying barrier impairment caused by cellular senescence and describe age-related barrier diseases associated with senescent cells. Finally, we summarize the currently used anti-senescence pharmacological interventions and discuss their therapeutic potential for preventing age-related barrier diseases.

Humoral and cellular factors inhibit phosphate-induced vascular calcification during the growth period

Hyperphosphatemia is an independent and non-classical risk factor of cardiovascular disease and mortality in patients with chronic kidney disease (CKD). Increased levels of extracellular inorganic phosphate (Pi) are known to directly induce vascular calcification, but the detailed underlying mechanism has not been clarified. Although serum Pi levels during the growth period are as high as those observed in hyperphosphatemia in adult CKD, vascular calcification does not usually occur during growth. Here, we have examined whether the defence system against Pi-induced vascular calcification can exist during the growth period using mice model. We found that calcification propensity of young serum (aged 3 weeks) was significantly lower than that of adult serum (10 months), possibly due to high fetuin-A levels. In addition, when the aorta was cultured in high Pi medium in vitro, obvious calcification was observed in the adult aorta but not in the young aorta. Furthermore, culture in high Pi medium increased the mRNA level of tissue-nonspecific alkaline phosphatase (TNAP), which degrades pyrophosphate, only in the adult aorta. Collectively, our findings indicate that the aorta in growing mouse may be resistant to Pi-induced vascular calcification via a mechanism in which high serum fetuin-A levels and suppressed TNAP expression.

25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) induces ectopic calcification

Vascular calcification is an important pathogenesis related to cardiovascular disease and high mortality rate in chronic kidney disease (CKD) patients. It has been well-known that hyper-phosphatemia induces osteochondrogenic transition of vascular smooth muscle cells (VSMCs) resulting ectopic calcification in aortic media, cardiac valve, and kidney. However, the detailed mechanism of the ectopic calcification has been not clarified yet. Here, we found that the co-localization of CYP27B1 with the calcified lesions of aorta and arteries in kidney of klotho mutant (kl/kl) mice, and then investigated the role of CYP27B1 in the mineralization of the VSMCs. Under high phosphate condition, overexpression of CYP27B1 induced calcification and osteocalcin mRNA expression in the VSMCs. Inversely, siRNA-CYP27B1 inhibited high phosphate-induced calcification of the VSMCs. We also found that the accumulated CYP27B1 protein was glycosylated in the kidney of kl/kl mice. Therefore, overexpression of CYP27B1-N310A and CYP27B1-T439A, which are a mutation for N-linked glycosylation site (N310A) and a mutation for O-linked glycosylation site (T439A) in CYP27B1, decreased calcium deposition and expression of RUNX2 induced by high phosphate medium in VSMCs compared with wild-type CYP27B1. These results suggest that extra-renal expression of glycosylated CYP27B1 would be required for ectopic calcification of VSMCs under hyperphosphatemia.

Phosphate and Cellular Senescence

Cellular senescence is one type of permeant arrest of cell growth and one of increasingly recognized contributor to aging and age-associated disease. High phosphate and low Klotho individually and synergistically lead to age-related degeneration in multiple organs. Substantial evidence supports the causality of high phosphate in cellular senescence, and potential contribution to human aging, cancer, cardiovascular, kidney, neurodegenerative, and musculoskeletal diseases. Phosphate can induce cellular senescence both by direct phosphotoxicity, and indirectly through downregulation of Klotho and upregulation of plasminogen activator inhibitor-1. Restriction of dietary phosphate intake and blockage of intestinal absorption of phosphate help suppress cellular senescence. Supplementation of Klotho protein, cellular senescence inhibitor, and removal of senescent cells with senolytic agents are potential novel strategies to attenuate phosphate-induced cellular senescence, retard aging, and ameliorate age-associated, and phosphate-induced disorders.

Understanding the Stony Bridge between Osteoporosis and Vascular Calcification: Impact of the FGF23/Klotho axis

A relationship between osteoporosis (OP) and vascular calcification (VC) is now proposed. There are common mechanisms underlying the regulation of them. Fibroblast growth factor- (FGF-) 23 and Klotho are hormones associated with the metabolic axis of osteovascular metabolism. Most recently, it was suggested that the FGF23-klotho axis is associated with increasing incidence of fractures and is potentially involved in the progression of the aortic-brachial stiffness ratio. Herein, we discussed the potential role of the FGF23/Klotho axis in the pathophysiology of OP and VC. We want to provide an update review in order to allow a better understanding of the potential role of the FGF23/Klotho axis in comorbidity of OP and VC. We believe that a better understanding of the relationship between both entities can help in proposing new therapeutic targets for reducing the increasing prevalence of OP and VC in the aging population.

Sugar sweetened beverage consumption is positively associated with Klotho levels at two years of age in LatinX youth

Background

Klotho is an anti-aging protein mainly expressed in the kidneys with a smaller amount expressed in adipose tissue. Klotho effects include roles in reducing oxidative stress, insulin signaling, adipogenesis and glucose metabolism. Few studies have investigated the role of dietary factors such as sugar sweetened beverages (SSBs) on serum α-klotho levels in young children.

Methods

Data was collected from 60 low-income Latina pregnant women and their infants in San Francisco from birth until 2 years of life and examined for associations between dietary factors and child secreted α-klotho protein levels at 2 years.

Results

Mean α-klotho levels were 1782.96 ± 874.56 pg/mL at 2 years of age. Any consumption of SSBs was independently associated with increased α-klotho levels (Beta = 682.79, 95%CI 67.50, 1298.09; p = 0.03). Household income ranging from $25,000 to $50,000 was also correlated to higher levels of α-klotho in children compared with lower income levels (<$25,000) (Beta = 1613.35, 95%CI 527.37, 2699.33; p = 0.005).

Conclusions

The positive association between SSB intake and α-klotho levels at 2 years may reflect higher phosphate levels consistent with SSB intake. Higher socioeconomic status may be a proxy for reduced stress exposure in children, also associated with higher α-klotho levels. Future studies should evaluate the early impact of exposures to SSBs, stress and accelerated aging in children.

The Clinical Value of Klotho and FGF23 in Cardiac Valve Calcification Among Patients with Chronic Kidney Disease

Objective

This study aims to investigate the clinical value of serum Klotho and FGF23 in cardiac valve calcification in patients with chronic kidney disease (CKD).

Methods

In the present study, 180 patients with CKD, who were admitted to the department of nephrology of our hospital on April 1, 2016 (solstice, 2019), were selected as the main subjects. According to the CKD stage, these patients were divided into three groups: CKD2~3 group, CKD4 group, and CKD5 group. In each group, ultrasound was used to evaluate the cardiac valve calcification, and the independent risk factors for cardiac valve calcification were analyzed by Logistic regression.

Results

The levels of hemoglobin and blood calcium in CKD2~3 patients were higher than those in CKD4 and CKD5 patients, and the levels of hemoglobin and blood calcium in CKD5 patients were higher than those in CKD4 patients (P<0.05). Albumin was lower in CKD2~3 patients when compared to CKD5 patients while albumin was higher in CKD5 patients when compared to CKD4 patients (P<0.05). The serum levels of FGF23 was lower in CKD2~3 patients when compared to CKD4 and CKD5 patients while the serum levels of FGF23 was lower in CKD4 patients when compared to CKD5 patients (P<0.05). The serum levels of Klotho was higher in CKD2~3 patients, when compared to CKD4 and CKD5 patients, while the serum levels of Klotho was higher in CKD4 patients, when compared to CKD5 patients (P<0.05). The logistic regression analysis revealed that GFR, serum creatinine, FGF23 and Klotho were independent risk factors for cardiac valve calcification in patients with CKD.

Conclusion

With the decrease of GFR in CKD patients, the serum levels of FGF23 increases, while the serum levels of Klotho decreases. Furthermore, the serum levels of FGF23 and Klotho are affected by various factors, and the levels of FGF23 and Klotho in CKD patients are negatively correlated. GFR, serum creatinine, FGF23 and Klotho are independent risk factors for heart valve calcification in patients with CKD.

High Phosphate Induces and Klotho Attenuates Kidney Epithelial Senescence and Fibrosis

Cellular senescence is an irreversible cell growth arrest and is associated with aging and age-related diseases. High plasma phosphate (Pi) and deficiency of Klotho contribute to aging and kidney fibrosis, a pathological feature in the aging kidney and chronic kidney disease. This study examined the interactive role of Pi and Klotho in kidney senescence and fibrosis. Homozygous Klotho hypomorphic mice had high plasma Pi, undetectable Klotho in plasma and kidney, high senescence with massive collagen accumulation in kidney tubules, and fibrin deposits in peritubular capillaries. To examine the Pi effect on kidney senescence, a high (2%) Pi diet was given to wild-type mice. One week of high dietary Pi mildly increased plasma Pi, and upregulated kidney p16/p21 expression, but did not significantly decrease Klotho. Two weeks of high Pi intake led to increase in plasminogen activator inhibitor (PAI)-1, and decrease in kidney Klotho, but still without detectable increase in kidney fibrosis. More prolonged dietary Pi for 12 weeks exacerbated kidney senescence and fibrosis; more so in heterozygous Klotho hypomorphic mice compared to wild-type mice, and in mice with chronic kidney disease (CKD) on high Pi diet compared to CKD mice fed a normal Pi diet. In cultured kidney tubular cells, high Pi directly induced cellular senescence, injury and epithelial-mesenchymal transition, and enhanced H₂O₂-induced cellular senescence and injury, which were abrogated by Klotho. Fucoidan, a bioactive molecule with multiple biologic functions including senescence inhibition, blunted Pi-induced cellular senescence, oxidation, injury, epithelial-mesenchymal transition, and senescence-associated secretary phenotype. In conclusion, high Pi activates senescence through distinct but interconnected mechanisms: upregulating p16/p21 (early), and elevating plasminogen activator inhibitor-1 and downregulating Klotho (late). Klotho may be a promising agent to attenuate senescence and ameliorate age-associated, and Pi-induced kidney degeneration such as kidney fibrosis.