An Acidic Environment Induces APOL1-Associated Mitochondrial Fragmentation.

Area of Science:

• Molecular Biology
• Genetics
• Nephrology

Background:

• Apolipoprotein L1 gene (APOL1) G1 and G2 kidney-risk variants (KRVs) are linked to chronic kidney disease (CKD) in African Americans.
• These variants induce mitochondrial dysfunction, but not all individuals with high-risk genotypes develop nephropathy, indicating the need for modifying factors.
• APOL1 function is pH-sensitive, and the kidney interstitium's naturally acidic pH (<7) may influence disease pathogenesis.

Purpose of the Study:

• To investigate the hypothesis that the acidic kidney interstitial environment exacerbates APOL1 KRV-induced mitochondrial dysfunction.
• To determine the role of pH in APOL1-mediated mitochondrial pathophysiology.

Main Methods:

• Human embryonic kidney (HEK293) cells expressing APOL1 G0 (reference), G1, or G2 KRVs, or an empty vector (EV), were cultured in media at pH 6.8 or 7.4.
• Cells were treated with doxycycline (Dox) for 4, 6, or 8 hours to induce variant expression.
• Mitochondrial length was measured using confocal microscopy and analyzed with Fiji software to assess fragmentation and dysfunction.

Main Results:

• After 6 hours in pH 6.8 media, G2-expressing cells showed significantly shorter mitochondria compared to EV and G0 controls.
• After 8 hours in pH 6.8 media, both G1 and G2 expressing cells exhibited significantly shorter mitochondria than EV and G0 controls.
• Mitochondrial length remained comparable across genotypes at pH 7.4, and APOL1 mRNA expression and cell viability were unaffected by pH or genotype.

Conclusions:

• Acidic pH significantly facilitates early mitochondrial dysfunction in HEK293 cells expressing APOL1 G1 and G2 KRVs.
• The acidic microenvironment of the kidney interstitium may contribute to APOL1-mediated mitochondrial dysfunction and the development of nephropathy.