High Phosphate Induces and Klotho Attenuates Kidney Epithelial Senescence and Fibrosis

Jenny Maique,Orson W Moe,Mingjun Shi,Ming Chang Hu,Zhiyong Zhou,Brianna Flores,Shirely Yan,Sierra Shepard

doi:10.3389/fphar.2020.01273

Jenny Maique, Orson W Moe + Show 6 more

Open Access

https://doi.org/10.3389/fphar.2020.01273

Copy DOI

Abstract

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.

Highlights

Cellular senescence is an irreversible cell-cycle arrest and serves as a defense mechanism to prevent cancer cell transformation, growth, and metastasis (Childs et al, 2015; Sturmlechner et al, 2017; Mchugh and Gil, 2018; Ovadya and Krizhanovsky, 2018; Calcinotto et al, 2019; Docherty et al, 2019)
We previously showed that high Pi decreases circulating and kidney Klotho and induces kidney fibrosis, while low Klotho increases plasma Pi and synergistically exacerbates kidney fibrosis induced by high Pi diet (Hu et al, 2015; Shi et al, 2020)
We examined in vivo and in vitro effects of Pi and Klotho on senescence and fibrosis, and explored the profile of changes in several key intermediates including CDK inhibitor p21 (p21), CDK4 inhibitor p16INK4 (p16), plasminogen activator inhibitor-1 (PAI-1), and senescence marker protein 30 (SMP30) in mice kidneys and cultured normal rat kidney (NRK) cells

Summary

Introduction

Cellular senescence ( termed senescence) is an irreversible cell-cycle arrest and serves as a defense mechanism to prevent cancer cell transformation, growth, and metastasis (Childs et al, 2015; Sturmlechner et al, 2017; Mchugh and Gil, 2018; Ovadya and Krizhanovsky, 2018; Calcinotto et al, 2019; Docherty et al, 2019). Compelling observational and animal studies showed that phosphotoxicity is associated with reduced longevity in several species (Kuro-O, 2010; Shi et al, 2020) and causes severely abnormal metabolism and ill effects on bone, kidney, cardiovasculature, and other organs in chronic kidney disease (CKD) (Kestenbaum et al, 2005; Tonelli et al, 2005; John et al, 2011; Calvo et al, 2019). The molecular mechanisms by which Pi mediates acceleration of aging, and initation and excerbation of cardiovascular disease in CKD are complex, multifactorial, and not fully understood (Ohnishi and Razzaque, 2010; Osuka and Razzaque, 2012; Hu et al, 2015; Ritter and Slatopolsky, 2016). Whether and how Pi modulates senescence is largely not understood

Methods

Results

Conclusion