New insights on the role of apoptosis and autophagy in HIV pathogenesis

Viruses manipulate host cells to ensure their own survival and, at late stages of the viral life cycle, they kill the infected target cell to ensure their propagation. In addition, some viruses induce a bystander killing, a viral strategy to escape from the host's innate and cognate defense systems. In HIV-infection, the disabling of the immune system is initially due to the preferential depletion by apoptosis of virus-specific CD4(+) T cells in lymphoid tissues, followed by the destruction of non-infected bystander cells. Both the extrinsic and the intrinsic pathways are activated, and this is the consequence of systemic immune activation. This review presents recent developments showing that the gastrointestinal tract is the major reservoir of infected cells and the site of rapid and profound loss of CD4 T cells, and that microbial translocation from the gastrointestinal tract is the cause of immune activation. Furthermore, apoptosis mechanisms involved in HIV-induced neuropathological disorders are discussed, including the role of syncytia that involve the sequential activation of ATM, p38MAPK and p53. Finally, HIV-associated dementia (HAD) was recently found in monkey models to be linked to inhibition of autophagy in neurons, suggesting that homeostasis of autophagy is a reliable security factor for neurons, and challenging the development of new therapeutics aimed at boosting neuronal autophagy to prevent HAD.