Deficiency in Apoptosis-Inducing Factor Recapitulates Chronic Kidney Disease via Aberrant Mitochondrial Homeostasis

Abstract

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein with dual roles in redox signaling and programmed cell death. Deficiency in AIF is known to result in defective oxidative phosphorylation (OXPHOS), via loss of complex I activity and assembly in other tissues. Because the kidney relies on OXPHOS for metabolic homeostasis, we hypothesized that a decrease in AIF would result in chronic kidney disease (CKD). Here, we report that partial knockdown of Aif in mice recapitulates many features of CKD, in association with a compensatory increase in the mitochondrial ATP pool via a shift toward mitochondrial fusion, excess mitochondrial reactive oxygen species production, and Nox4 upregulation. However, despite a 50% lower AIF protein content in the kidney cortex, there was no loss of complex I activity or assembly. When diabetes was superimposed onto Aif knockdown, there were extensive changes in mitochondrial function and networking, which augmented the renal lesion. Studies in patients with diabetic nephropathy showed a decrease in AIF within the renal tubular compartment and lower AIFM1 renal cortical gene expression, which correlated with declining glomerular filtration rate. Lentiviral overexpression of Aif1m rescued glucose-induced disruption of mitochondrial respiration in human primary proximal tubule cells. These studies demonstrate that AIF deficiency is a risk factor for the development of diabetic kidney disease.

Targeted mitochondrial therapy using MitoQ shows equivalent renoprotection to angiotensin converting enzyme inhibition but no combined synergy in diabetes

“…Previous studies have identified mitochondrial dysfunction 13 , 17 , 19 , 21 , 27 , 37 , including increases in mitochondrial OCR as early pathological events in the kidneys of diabetic rodents 11 , 13 . In agreement, we have now shown that mitochondria isolated from kidney cortices of diabetic mice have increased OCR and electron flow specifically at complexes II through to IV of the electron respiratory chain, most likely due to impairment of complex I activity, which has been previously shown in the diabetic kidney 13 , 38 .…”

“…Early (four weeks) and later (nine weeks) during treatment intervention, mice were acclimatised and metabolically caged for 24 h to determine food and water intake and collect urine. Urinary albumin and creatinine assays were performed on timed urine collections 37 . Plasma glucose, insulin and glycated hemoglobin were assessed at the beginning and end of the treatment as previously described 58 .…”

To study the effect of taurine on the effects of vital bones and regulate the level of glucose in type II diabetes

“…The independent sample t-test was used to the comparison between groups and paired t-test, was used to ind the signi icant difference between pre-and after treatment values within each group, p-value < 0.05 was considered as signi icant (Coughlan et al, 2016).…”

Exploring the role of the metabolite-sensing receptor GPR109a in diabetic nephropathy

“…Kidney sections (3 μm) were stained with periodic acid-Schiff (PAS) and assessed in a semiquantitative manner, whereby a blinded researcher assessed the level of glomerulosclerosis for each glomerulus and assigned an integer score of between 1 and 4, indicative of the level of severity of glomerulosclerosis. Twenty-five glomeruli were scored per animal, and these scores were averaged to provide a glomerulosclerosis score index (GSI) for each animal, as previously described [28]. Ileal sections were fixed in 4% paraformaldehylde for 24 hours, followed by a transfer to 4% sucrose, and subsequent embedding in paraffin.…”

“…RNA was isolated from snap frozen ileum sections using a phenol-chloroform extraction method and used to synthesise cDNA, as previously described [28]. Gene expression of zonulin and occludin was determined using TaqMan (Life Technologies) and SYBR Green reagents (Applied Biosystems), respectively.…”