Abstract
Five pathogenic variants in the gene encoding cytochrome c (CYCS) associated with mild autosomal dominant thrombocytopenia have been reported. Previous studies of peripheral blood CD34+ or CD45+ cells from subjects with the G42S CYCS variant showed an acceleration in megakaryopoiesis compared to wild-type (WT) cells. To determine whether this result reflects a common feature of the CYCS variants, the c.145T>C mutation (Y49H variant) was introduced into the endogenous CYCS locus in K-562 cells, which undergo megakaryocytic maturation in response to treatment with a phorbol ester. The c.145T>C (Y49H) variant enhanced the megakaryocyte maturation of the K-562 cells, and this effect was seen when the cells were cultured at both 18 % and 5 % oxygen. Thus, alteration of megakaryopoiesis is common to both the G42S and Y49H CYCS variants and may contribute to the low platelet phenotype. The Y49H CYCS variant has previously been reported to impair mitochondrial respiratory chain function in vitro, however using extracellular flux analysis the c.145T>C (Y49H) variant does not alter mitochondrial bioenergetics of the K-562 cells, consistent with the lack of a phenotype characteristic of mitochondrial diseases in CYCS variant families. The Y49H variant has also been reported to enhance the ability of cytochrome c to trigger caspase activation in the intrinsic apoptosis pathway. However, as seen in peripheral blood cells from G42S CYCS variant carriers, the presence of Y49H cytochrome c in K-562 cells did not significantly change their response to an apoptotic stimulus.