TcHTE expression is regulated by intracellular heme levels in Trypanosoma cruzi

JULIA A. CRICCO; EVELYN TEVERE; CECILIA B. DI CAPUA

Congreso; Molecular Parasitology Meeting XXI; 2020

Genetics Society of America

Trypanosoma cruzi is a heme auxotroph organism and rely on the acquisition of this cofactor from their mammalian host or insect vector. Inside of the insect vector, T. cruzi may be in contact with hemoglobin (Hb) and heme derived from blood digestion. In vitro, T. cruzi epimastigotes can use both hemin and Hb as a heme source, which are internalized via different pathways. However, little is known about the use of Hb as a heme source.TcHTE (T. cruzi Heme Transport Enhancer) is a protein belonging to the Heme Response Gene family. This protein is involved in heme uptake, probably being part of a heme transporter and controlling this activity. TcHTE is expressed mainly in the replicative life cycle stages of the parasites and it is localized to the flagellar pocket in epimastigotes. In this work, we studied the role of TcHTE in heme homeostasis in Hb-supplemented parasites.Conversely to the growth and morphology alterations in parasites supplemented with high hemin concentrations, epimastigotes tolerate high Hb concentrations in the medium and exhibit a typical morphology in these conditions. At mRNA and protein level, TcHTE is higher in heme-starved parasites and decreases when hemin or Hb are added to the medium. However, the response is less severe when Hb is used as heme source.Surprisingly, epimastigotes that overexpress rTcHTE.His-GFP incubated in Hb-supplemented medium have a significantly higher intracellular heme compared to control epimastigotes; as previously reported in hemin-supplemented parasites. In addition, rTcHTE.His-GFP does not change its localization in Hb-supplemented parasites. We concluded that T. cruzi is able to sense intracellular heme levels and regulates TcHTE expression according to it, independently of the heme source (hemin or Hb). Based on these and our previous results, we propose two complementary models of heme uptake in T. cruzi. In the first one, Hb is endocytosed and internally degraded. In the second one, Hb is externally degraded by parasite proteases and released heme enters the cell via TcHTE. The second model would explain why over-expression of rTcHTE.His-GFP produces an increase in the intracellular heme in Hb-supplemented parasites. In both models, once the parasite satisfies its heme requirements, TcHTE expression (and therefore heme transport) decreases.