Circular RNAs as a new perspective in the diagnosis and mechanism of Leishmania infections.

Leishmaniasis is a neglected infectious disease that affects millions of people worldwide. Visceral leishmaniasis (VL) caused by Leishmania infantum and cutaneous leishmaniasis (CL) caused by L. major/ L. tropica are the main clinical forms of this disease, which are life-threatening if not diagnosed and treated properly. Considering the problems in sampling and laboratory diagnosis of leishmaniasis, new molecular markers such as circular RNAs (circRNAs) are needed. circRNAs, a novel class of RNAs, have been one of the most promising targets for the diagnosis and prognosis of diseases. Although the therapeutic and diagnostic role of circRNAs in many diseases and some parasitic diseases are known, not much research has been done in the field of leishmaniasis. We determined the gene expressions of circRNAs in human leukemia monocytic (THP-1) cells after infection with Leishmania. For this, the human cell line THP-1 was differentiated into macrophages by Phorbol 12-myristate 13-acetate (PMA) treatment. Differentiated THP-1 cells were infected with L. infantum and L. tropica promastigotes. After 24 hours, expression levels of circRNAs were determined by RT-qPCR technique. Also, the microRNAs associated with differentially expressed circRNAs were investigated. Then, the molecular pathways associated with expressed circRNAs were obtained by GO and Reactome. The results showed that five circRNAs were differentially expressed in THP1 macrophages infected with L. infantum and L. tropica. These findings suggest that some circRNAs may be potential biomarkers for diagnosis in Leishmania-infected patients. The enrichment analysis revealed that differentially expressed circRNAs are mainly involved in the regulation of protein stability, RNA catabolic process, and P53/PTK6 signaling mechanism. This is the first study to report an overview of Leishmania-induced circRNAs, which can be potential biomarker candidate for diagnosis especially at species level. Notably, expression of some circRNAs in supernatant of Leishmania infected macrophages suggests that these genes are available in body fluids, therefore, can easily be accessed from the patient without invasive methods especially during treatment monitoring.