An Acidic Environment Inducesapol1-Associated Mitochondrial Fragmentation

Background:Apolipoprotein L1 gene (APOL1) G1 and G2 kidney-risk variants (KRVs) cause CKD in African Americans, inducing mitochondrial dysfunction. Modifying factors are required, because a minority of individuals withAPOL1high-risk genotypes develop nephropathy. Given that APOL1 function is pH-sensitive and the pH of the kidney interstitium is <7, we hypothesized the acidic kidney interstitium may facilitateAPOL1KRV-induced mitochondrial dysfunction.Methods:Human embryonic kidney (HEK293) cells conditionally expressing empty vector (EV),APOL1-reference G0, and G1 or G2 KRVs were incubated in media pH 6.8 or 7.4 for 4, 6, or 8 h. Genotype-specific pH effects on mitochondrial length (mu m) were assessed using confocal microscopy in live cells and Fiji derivative of ImageJ software with MiNA plug-in. Lower mitochondrial length indicated fragmentation and early dysfunction.Results:After 6 h doxycycline (Dox) induction in pH 6.8 media, G2-expressing cells had shorter mitochondria (6.54 +/- 0.40) than cells expressing EV (7.65 +/- 0.72,p= 0.02) or G0 (7.46 +/- 0.31,p= 0.003). After 8 h Dox induction in pH 6.8 media, both G1- (6.21 +/- 0.26) and G2-expressing cells had shorter mitochondria (6.46 +/- 0.34) than cells expressing EV (7.13 +/- 0.32,p= 0.002 andp= 0.008, respectively) or G0 (7.22 +/- 0.45,p= 0.003 andp= 0.01, respectively). Mitochondrial length in cells incubated in pH 7.4 media were comparable after 8 h Dox induction regardless of genotype.APOL1mRNA expression and cell viability were comparable regardless of pH or genotype after 8 h Dox induction.Conclusion:Acidic pH facilitates early mitochondrial dysfunction induced byAPOL1G1 and G2 KRVs in HEK293 cells. We propose that the acidic kidney interstitium may play a role inAPOL1-mediated mitochondrial pathophysiology and nephropathy.