Trypanosoma cruzi, a heme auxotrophic parasite, can control intracellular heme content by modulating heme responsive gene (TcHRG) expression when a free heme source is added to an axenic culture. Herein, we explored the role of TcHRG protein in regulating the uptake of heme derived from hemoglobin in epimastigotes. We demonstrate that the endogenous TcHRG (protein and mRNA) responded similarly to bound (hemoglobin) and free (hemin) heme. Endogenous TcHRG was found in the flagellar pocket boundaries and partially overlapping with the mitochondrion. On the other hand, endocytic null parasites were able to develop and exhibited a similar heme content compared to wild-type when fed with hemoglobin, indicating that endocytosis is not the main entrance pathway for hemoglobin-derived heme in this parasite. Moreover, the overexpression of TcHRG led to an increase in heme content when hemoglobin was used as the heme source. Taken together, these results suggest that the uptake of hemoglobin-derived heme likely occurs through extracellular proteolysis of hemoglobin via the flagellar pocket, and this process is governed by TcHRG. In sum, T. cruzi epimastigotes control heme homeostasis by modulating TcHRG expression independently of the available source of heme.

中文翻译：

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克氏锥虫血红素反应基因 (TcHRG) 在协调上鞭毛体血红素摄取中发挥核心作用

克氏锥虫是一种血红素营养缺陷型寄生虫，当向无菌培养物中添加游离血红素源时，可以通过调节血红素反应基因 ( Tc HRG) 的表达来控制细胞内血红素含量。在此，我们探讨了Tc HRG 蛋白在调节上鞭毛体对源自血红蛋白的血红素的摄取中的作用。我们证明内源Tc HRG（蛋白质和 mRNA）与结合（血红蛋白）和游离（血红素）血红素的反应相似。内源Tc HRG 发现于鞭毛袋边界并与线粒体部分重叠。另一方面，当用血红蛋白喂养时，内吞无效寄生虫能够发育并表现出与野生型相似的血红素含量，这表明内吞作用不是该寄生虫中血红蛋白衍生血红素的主要入口途径。此外，当使用血红蛋白作为血红素来源时，Tc HRG 的过度表达导致血红素含量增加。总而言之，这些结果表明血红蛋白衍生的血红素的摄取可能是通过鞭毛袋对血红蛋白进行细胞外蛋白水解而发生的，并且该过程受Tc HRG 控制。总之，克氏锥虫上鞭毛体通过独立于可用血红素来源调节Tc HRG 表达来控制血红素稳态。