Human Cytomegalovirus Inhibited Megakaryocytic Differentiation, Maturation and Induced Apoptosis in Vitro.

Abstract 2413

Poster Board II-390

Human cytomegalovirus (HCMV) can cause life-threatening infection in immunocomprimised individuals, such as patients undergoing intensive chemotherapy or bone marrow transplantation. Thrombocytopenia is one of the manifestations in active HCMV infection, which may be a consequence of viral suppression on megakaryopoiesis. The exact underline mechanisms remain uncertain. Our previous studies suggested that HCMV directly infects megakaryocytic progenitors and inhibits their proliferation. Colony-formation of HCMV-infected CFU-MK decreased in a dose-dependent manner (Blood, 2003, abstract). In present study, we explored the mechanisms further by using a phorbol 12-myristate 13-acetate (PMA) stimulating polyploidization to mimic the late stage of megakaryocytic differentiation and maturation in vitro. After co-culture of a megakaryocytic cell line CHRF-288-11 with HCMV AD169 experimental strain from day 0 to day 3 (multiple of infection, MOI=1), the polyploidization of megakaryocyte was determined by DNA content analysis using flow cytometry. Compared with negative control, the proportion of polyploidy (ploidy N ≥ 8) megakaryocytes decreased by 52%, 32% and 16% in HCMV-infected cell at day 3, day 6 and day 9 respectively. As a specific receptor for megakaryopoietic differentiation, the c-Mpl protein (TPO receptor) was also examined in CHRF-288-11 cell line. The proportion of c-Mpl positive cells showed a 23% decrease in HCMV-infected group in compared to the mock infection control (using ultralviolet treated HCMV) at day 5. In addition, apoptotic signals from megakaryocytic surface, cytoplasma and mitochondria were detected in HCMV-infected cells by flow cytometry with Annexin V, Caspase-3 and JC-1 assay. Compared to mock infection control at day 5, annexin-V positive cells population increased by 57%; active caspase-3 signal increased by 125% in viable cell population; and cell population with damaged mitochondial membrane showed a 5-times increase. In conclusion, our data demonstrated that: (1) HCMV inhibited megakaryocytic differentiation and maturation at late stage; (2) HCMV reduced c-Mpl positive cell population; (3) HCMV induced megakaryocytic apoptosis through intrinsic apoptotic pathway as shown by the functional alteration of mitochodial membrane, activation of caspase-3 and structural damage of outer cellular membrane. HCMV-induced thrombocytopenia is the consequence of multiple processes involving inhibition of megakaryocytic proliferation, differentiation, maturation and also increased megakaryocytic apoptosis.