Mouse embryonic fibroblasts devoid of both mitofusin1 and mitofusin2 can acutely shift from glycolytic to oxidative metabolism.

Abstract

The extent to which a deficiency of mitochondrial fusion is required for oxidative metabolism is unclear. To this end, we have undertaken a bioenergetics analysis using intact mouse embryonic fibroblasts deficient in mitofusin1 and mitofusin2 (DKO) incubated with glycolytic vs. oxidative substrate. We first noted a ~doubling of non‐mitochondrial oxygen consumption (JO2) in DKO cells, regardless of substrate. Upon switching from glycolytic to oxidative conditions, both Wt and DKO MEFs increased basal mitochondrial JO2 (oligomycin‐sensitive+oligomycin‐insensitive, non‐mitochondrial subtracted), although the rise was smaller in DKO cells (increase of 55±11 vs. 114±11 pmoles/min/40k cells in DKO vs. Wt; mean±sem). Considering only oligomycin‐sensitive JO2, the rise was similar in DKO cells (increase of 121.3±10 vs. 135.8±13 pmoles O2/min/40k cells in DKO vs. Wt), whereas oligomycin‐insensitive JO2 decreased in DKO cells only (by ~50%). In both Wt and DKO cells, the rate of media acidification declined upon switching from glycolytic to oxidative substrate, indicating a shift from glycolytic to oxidative ATP production. Thus, as in Wt MEFs, DKO MEFs demonstrate basal mitochondrial respiration controlled by ATP turnover, and substrate oxidation. Differently from the Wt, DKO mitochondria exert significant control over basal JO2 by proton leak, which would function to expand capacity.