Human lung epithelial cells support human metapneumovirus persistence by overcoming apoptosis

Abstract

Human metapneumovirus (hMPV) has been identified as a major cause of lower respiratory tract infection in children. Epidemiological and molecular evidence has highlighted an association between severe childhood respiratory viral infection and chronic lung diseases, such as asthma and chronic obstructive pulmonary disease. Currently, animal models have demonstrated the ability of hMPV to persist in vivo suggesting a role of the virus in asthma development in children. However, mechanisms involved in hMPV persistence in the respiratory tract are not yet understood. In the present study we monitored hMPV infection in human alveolar epithelial A549 cells in order to understand if the virus is able to persist in these cells upon acute infection. Our data show that hMPV initially induces an apoptotic process in A549 cells through poly (ADP-ribose) polymerase 1 cleavage, caspase-3/7 activation and Wee1 activity. The hMPV-infected cells were then able to overcome the apoptotic pathway and cell cycle arrest in G2/M by expressing B-cell lymphoma 2 and to acquire a reservoir cell phenotype with constant production of infectious virus. These findings provide evidence of the ability of hMPV to persist in alveolar epithelial cells and help in understanding the mechanisms responsible for hMPV persistence in the human respiratory tract.

Cell-Mediated Responses to Human Metapneumovirus Infection

“…In general, viruses may be able to persist by interfering with the induction of apoptosis. Supporting that, chronic hMPV infection in AECs increased expression of the anti-apoptotic Bcl-2 protein, which overthrows the apoptotic program [89].…”

“…It is important to note that hMPV persistence has only been described in some mouse studies [54,[91][92][93] and a few immunocompromised patients of which some had no symptoms [42,43,94]. Additionally, hMPV persistence has been described in vitro in A549 cells by Marsico et al [89]. This study showed that at 14 dpi, the hMPV-infected cells were still metabolically active which could represent the beginning of coexistence between AECs and hMPV and thus transition from acute to persistent infections.…”

“…Marsico et al monitored the behavior of AECs during acute hMPV infection (based on the protocol of Bao et al [58]) using A549 cells and showed massive cell death characterized by apoptotic nuclei and DNA fragmentation during the first three days and up to seven days post infection (dpi). Moreover, the caspase-3 and -7 activity gradually increased up to 7 dpi, and a role for phosphorylation of the Wee1 kinase in the hMPV-driven apoptosis could be identified [89]. Interestingly, the caspase activity decreased at 14 dpi, and the residual epithelial cells at that time point seem to reverse the apoptotic process.…”

Human Metapneumovirus: Mechanisms and Molecular Targets Used by the Virus to Avoid the Immune System

“…Typically, death of infected host cells implies a reduction in viral replication and an increase in the capacity of antigen presentation by immune cells. A study performed by Marsico et al described in human alveolar epithelial A549 cells that hMPV is able to persist through the inhibition of the apoptosis machinery ( 24 ). This effect was associated with an increase in the expression of Bcl-2, an antiapoptotic factor from the Bcl-2 family, in the surface of hMPV-infected cells after 14 days of infection.…”

“…This effect was associated with an increase in the expression of Bcl-2, an antiapoptotic factor from the Bcl-2 family, in the surface of hMPV-infected cells after 14 days of infection. In addition, the authors postulated a direct correlation between cellular survival and viral replication, suggesting that hMPV starts its infective cycle with a strong peak of replication and a significant increase in cellular apoptosis, followed by a decrease in viral infective rates, promoting a slow cellular proliferation, overcoming apoptosis and inducing cell cycle arrest in G2/M ( 24 ). On the other hand, hRSV-infection has been associated with an early induction of Mcl-1 -another antiapoptotic factor that belongs to the Bcl-2 family- along with more antiapoptotic factors (Bcl-W, Bcl-xL) and pro-apoptotic factors (Bid, Bax, Bak), which all could be mediated by the NF-κB pathway ( 25 ), suggesting that hMPV could also be using others factor from the Bcl-2 family.…”