Epigenetic regulation of defense genes by histone deacetylase1 in human cell line-derived macrophages promotes intracellular survival of Leishmania donovani

Abstract

Leishmania donovani, an intracellular protozoan parasite upon infection, encounters a range of antimicrobial factors within the host cells. Consequently, the parasite has evolved mechanisms to evade this hostile defense system through inhibition of macrophage activation that, in turn, enables parasite replication and survival. There is growing evidence that epigenetic down-regulation of the host genome by intracellular pathogens leads to acute infection. Epigenetic modification is mediated by chromatin remodeling, histone modifications, or DNA methylation. Histone deacetylases (HDACs) removes acetyl groups from lysine residues on histones, thereby leading to chromatin remodeling and gene silencing. Here, using L. donovani infected macrophages differentiated from THP-1 human monocytic cells, we report a link between host chromatin modifications, transcription of defense genes and intracellular infection with L. donovani. Infection with L. donovani led to the silencing of host defense gene expression. Histone deacetylase 1 (HDAC1) transcript levels, protein expression, and enzyme activity showed a significant increase upon infection. HDAC1 occupancy at the promoters of the defense genes significantly increased upon infection, which in turn resulted in decreased histone H3 acetylation in infected cells, resulting in the down-regulation of mRNA expression of host defense genes. Small molecule mediated inhibition and siRNA mediated down-regulation of HDAC1 increased the expression levels of host defense genes. Interestingly, in this study, we demonstrate that the silencing of HDAC1 by both siRNA and pharmacological inhibitors resulted in decreased intracellular parasite survival. The present data not only demonstrate that up-regulation of HDAC1 and epigenetic silencing of host cell defense genes is essential for L. donovani infection but also provides novel therapeutic strategies against leishmaniasis. Author summary Visceral leishmaniasis is a neglected tropical disease caused by the protozoan parasite Leishmania donovani. These intracellular parasites replicate inside phagolysosomes of the macrophages and have evolved mechanisms that allow survival within the hostile environment of their hosts. They have evolved strategies to dramatically modify the transcriptome and proteome content of the host cells they infect, facilitating their survival within the host cell. Here, we have defined a mechanism by which Leishmania donovani subverts host cell defense genes by manipulating the epigenetic control of defense gene expression. The intracellular protozoan parasite, Leishmania, results in gene silencing of innate host defense genes. The underlying molecular mechanisms assisting such modifications were inferred from the results. An increase in the transcript, protein levels and activity of host HDAC1 was observed at 6 h post-infection. This data confirms the role of HDAC1 in the silencing of the host defense genes and enabling the intracellular survival of the parasite. Our results decode a new insight into epigenetic regulation of host cell defense mechanisms. These findings will facilitate the identification of novel strategies and will promise newer ways to control parasite growth.