Transcriptomic dynamics reveals sequential acquisition of complement resistance during prolonged starvation of...

The life cycle of the parasitic protozoan Trypanosoma cruzi, the etiological agent of Chagas disease (CD), includes two well-recognised insect-dwelling stages: the replicative non-infective epimastigotes and the non-replicative infective metacyclic trypomastigotes. Nonetheless, the existence of multiple intermediate forms has been reported. Since nutrient restriction is considered one of the main factors driving metacyclogenesis and is very frequent due to the long-term starvation periods that the insect vectors commonly undergo, we have studied the transcriptomic effects of nutrient restriction on long-lasting epimastigote cultures. We previously reported that in these conditions, we observed a long stationary phase characterised by an RNA content per cell three times smaller than the epimastigote's and a distinctive transcriptomic profile. Remarkably, our study identified gene expression changes that distincty characterise transitional parasite forms enriched by nutrient restriction.

In this work we focused on pathogenic genes to further characterise the transcriptomic dynamics accompanying the nutrient restriction within the insect-dwelling parasite stage.

The alterations of morphology, growth rate and complement resistance of parasite population on long-lasting epimastigote cultures as well as the transcriptomic dynamics was studied.

We found a gene expression early rise of surface proteins (such as trans-sialidase and GP63) and even a rise of TcTASV and δ-amastin, which is not accompanied by increased expression of metacyclic transcript markers. In addition, we found increased expression of genes coding for proteins involved in two other processes activated during the differentiation of epimastigotes to the infective form of the parasite: autophagy (Atg4, Atg7, Atg8.2) and complement resistance (TcCRP and T-DAF).

Altogether, these results, plus our previous identification of transcriptomic markers for transitional parasites, further support earlier proposals of a specific parasite stage that morphologically resembles epimastigotes but exhibits distinctive biological characteristics, including key features related to infectivity.