Deregulated megakaryocytic maturation, mitochondrial function and inflammatory signalling in CYCS(c.292T>C)-related thrombocytopenia

The human CYCS gene encodes for Cytochrome C, a mitochondrial protein with important cellular functions, including apoptosis and energy production. CYCS variants have been linked to CYCS-related thrombocytopenia, a mild autosomal dominant type of inherited thrombocytopenia. Here we report a novel heterozygous variant of the CYCS gene, c.292T>C, p.(Tyr98His) in a Greek family with thrombocytopenia. The functional role of the novel variant has been examined in several cellular processes to delineate the mechanisms underlying the thrombocytopenic phenotype of the patients. In megakaryocytes, the novel variant has been associated with irregular apoptosis, ATP production, superoxidase activity and maturation. Transcriptomic data have validated the deregulation of these cellular processes and have provided information about the effect of the variant on Tumor Necrosis Factor A (TNFA) signaling. TNFA via Nuclear Factor Kappa B (NFKB) pathway has been positively enriched in megakaryocytes carrying the variant, possibly triggering the observed deregulation of apoptosis and differentiation. This study has provided insights on the novel CYCS variant revealing a connection to the thrombocytopenic phenotype through deregulated apoptosis, energy production, differentiation and TNFA via NFKB signaling in megakaryocytes, providing future opportunities to therapeutically target the deregulated pathways in CYCS-related thrombocytopenias. Overall design: To model the effect of the novel CYCS (NM_018947.6):c.292T>C (p.Tyr98His) variant in megakaryocytic the (NM_018947.6):c.292T>C (p.Tyr98His) variant has been inserted in Dami cells through Homology-directed repair using the CRISPR-Cas9 System. Differential gene expression analysis was performed using data obtained from RNA-seq of 4 homozygous, 5 heterozygous mutant Dami clones and 4 wild type Dami clones (2 separate analyses: a. Homozygous vs Wild type b. Heterozygous vs Wild type)