Leishmania infantum Induces Mild Unfolded Protein Response in Infected Macrophages

Abstract

The Leishmaniases are a group of parasitic diseases caused by protozoa of the Leishmania genus affecting both humans and other vertebrates. Leishmania is an intracellular pathogen able to confer resistance to apoptosis in the early phase of macrophages infection by activation of host PI3K/Akt pathway and inhibition of caspase-3 activation. Intracellular pathogens hijack organelles such as ER to facilitate survival and replication, thus eliciting ER stress and activating/modulating the unfolded protein response (UPR) in the host cell. The UPR is aimed to mitigate ER stress, thereby promoting cell survival. However, prolonged ER stress will activate the apoptotic pathway. The aim of this study was to investigate the ER stress response in Leishmania-infected macrophages to gain insights about the mechanisms underlying the apoptosis resistance in parasitized cells. Macrophages differentiated from human monocytic cell lines (U937 and THP-1) and murine primary macrophages were infected with Leishmania infantum MHOM/TN/80/IPT1 (WHO international reference strain). Several ER stress/autophagy expression markers, as well as cell survival/apoptosis markers (phospho-Akt and cleaved caspase-3) were evaluated by qPCR and/or by western blotting. As ER stress positive control, cells were treated with tunicamycin or dithiothreitol (DTT). The gene expression analyses showed a mild but significant induction of the ER stress/autophagy markers. The western blot analyses revealed that the Leishmania infection induced Akt phosphorylation and significantly inhibited the induction of caspase-3 cleavage, eIF2α phosphorylation and DDIT3/CHOP expression in tunicamycin and DTT treated cells. The mild but significant increase in ER stress expression markers and the delay/attenuation of the effects of ER stress inducers in infected cells support the hypothesis that L. infantum could promote survival of host cells by inducing a mild ER stress response. The host ER stress response could be not only a common pathogenic mechanism among Leishmania species but also a target for development of new drugs.

Endoplasmic Reticulum Stress and Unfolded Protein Response in Infection By Intracellular Parasites

“…More recently, we showed that L. infantum infection induce a mild UPR in U937-derived macrophages [ 68 ], confirming – although with some differences – the activation of IRE1-XBP1 arm of UPR observed in infection by L. amazonensis . Moreover, a potential involvement of the PERK–ATF4 branch of UPR during Leishmania infection was also evidenced since ATF4 , as well as downstream genes such as ATF3 and CHOP were significantly upregulated [ 68 ]. It is known that the PERK/eIF2α/ATF4 pathway plays a key role in autophagy regulation.…”

“…showed that L. amazonensis induces autophagy in macrophages and that its inhibition with 3-methyladenine reduced the infection index, suggesting that the autophagic process could provide nutrition to the parasite [ 85 ]. We found that MAP1LC3B was significantly induced in U937-derived macrophages infected by L. infantum [ 68 ]. Therefore, it is likely that also the PERK–ATF4 branch of the UPR could have a role in Leishmania infection (e.g., induction of autophagic process).…”

“…It is known that low levels of ER stress may be beneficial to cells by eliciting a mild (adaptive) UPR, which can increase the cellular resistance to subsequent ER stress (ER hormesis) [ 86 ]. We found that the effects of ER stress inducers tunicamycin and DTT (i.e., eIF2α phosphorylation and CHOP protein induction) were attenuated/delayed in U937 and THP1-derived macrophages infected by L. infantum , accounting for a protective role of host UPR at least in the initial phase of infection [ 68 ]. This can further point out the role of IRE1-XBP1 and PERK-ATF4 arms of the UPR in Leishmania infection, since both these arms contribute to the ER hormesis.…”

Emerging Role for the PERK/eIF2α/ATF4 in Human Cutaneous Leishmaniasis

“…Regarding to intracellular parasites, it has been shown that Plasmodium berghei infection activates the XBP-1 signaling, which favors infection in the liver 15 . Additionally, it was recently reported that Leishmania infantum induces mild ER stress to promote parasite survival 31 . Here, we report that the PERK/eIF2α/ATF4 branch of the IERSR is activated during Leishmania infection and that this signaling has an essential role for parasite survival and proliferation.…”

Rapamycin Re-Directs Lysosome Network, Stimulates ER-Remodeling, Involving Membrane CD317 and Affecting Exocytosis, in Campylobacter Jejuni-Lysate-Infected U937 Cells

“…The expression of CHOP was monitored by qPCR using RT 2 SYBR Green ROX FAST Mastermix (Qiagen, Hilden, Germany) in a RotorGene 6000 instrument (Corbett life science, Sydney, Australia), as described previously [103]. A non-template control was included in duplicate for each primer pair reaction, as a negative control.…”