GDF15 and Mitochondrial myopathy: In a mouse model of mitochondrial myopathy driven by accumulation of mitochondrial DNA mutations, Gdf15 is upregulated early alongside Fgf21 in what the authors termed the “first-phase” of the mitochondrial ISR, which seems to be independent of ATF3, ATF4, and ATF5, as these were either not induced in this model or were induced after GDF15.