OCT4 Expression Mediates Partial Cardiomyocyte Reprogramming of Mesenchymal Stromal Cells

YANNARELLI, GG; PACIENZA, N; MONTANRI, S; SANTA CRUZ, DM; SOWMYA, V; KEATING, A

Congreso; ISSCR 2015; 2015

Mesenchymal stromal cells (MSCs) are in numerous celltherapy clinicaltrials, including for injured myocardium. The acquisition ofsome cardiomyocyte characteristics by MSCs canimprovecardiac regenerationbutthe mechanisms regulating this processare unclear.Theaim of our study was todetermine whether the expression of the pluripotencytranscription factor OCT4 is involved inthe activation of cardiac lineagegenetic programs in MSCs. We employed our established co-culture model of MSCswith embryonic cardiomyocytes showing co-expression of cardiac markers on MSCsindependent of cell fusion. Bone marrow-derived MSCs were isolatedfromtransgenic mice expressing greenflorescent protein(GFP) under control of thecardiac-specific a-myosin heavychainpromoter and co-cultured with rat embryonic cardiomyocytes.After 5 days of co-culture,MSCs expressed cardiac specific genes including Nkx2.5, atrial natriureticfactor and a-cardiac actin. Thefrequency of GFP+ cells was 7.6±2.3%, however, these cells retained the stromalcell phenotype, indicating partial differentiation.Global OCT4 expressionincreased 2.6±1.2-fold in co-cultured vs untreated MSCs (p<0.05)andof interest, 87±3% vs79±2% (p<0.05) of MSCs expressed OCT4 byflowcytometryin controlsand after co-culture, respectively. Consistent with thelatter observation, the GFP+ cellsdid not express nuclear OCT4 and showed asignificant increase in OCT4 promoter methylation compared with untreated MSCs(93% vs 47%, p<0.05), inferringthat OCT4 is regulated by an epigeneticmechanism. We further showed that siRNA silencing of OCT4 in MSCs(by 67%)resulted in a reduced frequency of GFP+ cells in co-culture to less than 1%.Moreover, differentiationof MSCs to adipocytes and osteocytes was reduced3-fold in OCT4-silenced MSCs versus controls. Our data infer that OCT4expression may have a direct effect on cardiac gene program activation in MSCsand also suggest new mechanism(s)mediating MSC multipotency.