Trichomonas vaginalis Macrophage Migration Inhibitory Factor Mediates Parasite Survival during Nutrient Stress

Trichomonas vaginalis is responsible for the most prevalent non-viral sexually transmitted disease worldwide, and yet the mechanisms used by this parasite to establish and maintain infection are poorly understood. We previously identified a T. vaginalis homologue (TvMIF) of a human cytokine, human macrophage migration inhibitory factor (huMIF). TvMIF mimics huMIF’s role in increasing cell growth and inhibiting apoptosis in human host cells. To interrogate a role of TvMIF in parasite survival during infection, we asked whether overexpression of TvMIF (TvMIF-OE) confers an advantage to the parasite under nutrient stress conditions by comparing the survival of TvMIF-OE parasites to that of empty vector (EV) parasites. We found that under conditions of serum starvation, overexpression of TvMIF resulted in increased parasite survival. Serum-starved parasites secrete 2.5-fold more intrinsic TvMIF than unstarved parasites, stimulating autocrine and paracrine signaling. Similarly, we observed that addition of recombinant TvMIF increased the survival of the parasites in the absence of serum. Recombinant huMIF likewise increased the parasite survival in the absence of serum, indicating that the parasite may use this host survival factor to resist its own death. Moreover, TvMIF-OE parasites were found to undergo significantly less apoptosis and reactive oxygen species (ROS) generation under conditions of serum starvation, consistent with increased survival being the result of blocking ROS-induced apoptosis. These studies demonstrated that a parasitic MIF enhances survival under adverse conditions and defined TvMIF and huMIF as conserved survival factors that exhibit cross talk in host-pathogen interactions.

Macrophage migration inhibitory factor (MIF) is a conserved protein found in most eukaryotes which has been well characterized in mammals but poorly studied in other eukaryotes. The limited analyses of MIF proteins found in unicellular eukaryotes have focused exclusively on the effect of parasitic MIF on the mammalian host. This was the first study to assess the function of a parasite MIF in parasite biology. We demonstrate that the Trichomonas vaginalis MIF functions to suppress cell death induced by apoptosis, thereby enhancing parasite survival under adverse conditions. Our research reveals a conserved survival mechanism, shared by a parasite and its host, and indicates a role for a conserved protein in mediating cross talk in host-pathogen interactions.

Improved survival of mesenchymal stem cells by macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a critical inflammatory cytokine that was recently associated with progenitor cell survival and potently inhibits apoptosis. We examined the protective effect of MIF on hypoxia/serum deprivation (SD)-induced apoptosis of mesenchymal stem cells (MSCs), as well as the possible mechanisms. MSCs were obtained from rat bone marrow and cultured in vitro. Apoptosis was induced by culturing MSCs under hypoxia/SD conditions for up to 24 h and assessed by flow cytometry. Expression levels of c-Met, Akt, and FOXO3a were detected by Western blotting. CD74 expression was detected by qRT-PCR, Western blot, and immunofluorescence. Oxidative stress under hypoxia/SD was examined by detection of reactive oxygen species (ROS) and activity of superoxide dismutase (SOD) and malondialdehyde (MDA). Hypoxia/SD-induced apoptosis was significantly attenuated by recombinant rat MIF in a concentration-dependent manner. MIF induced CD74-asssociated c-Met activation, which was blocked by knocking down CD74 expression using siRNA. MIF also induced Akt and associated FOXO3a phosphorylation, and this effect was abolished by knocking down either CD74 or Akt. In addition, MIF decreased oxidative stress in MSCs, as shown by decreased ROS and MDA, and increased the activity of SOD. Knockdown of CD74, Akt, or FOXO3a largely attenuated the anti-apoptotic effect of MIF and its ability to protect against oxidative stress. MIF protected MSCs from hypoxia/SD-induced apoptosis by interacting with CD74 to stimulate c-Met, leading to downstream PI3K/Akt-FOXO3a signaling and decreased oxidative stress.