Transcriptional Analysis of Human Skin Lesions Identifies Tryptophan-2,3-Deoxygenase as a Restriction Factor for Cutaneous Leishmania

Abstract

Disease manifestation after infection with cutaneous Leishmania species is the result of a complex interplay of diverse factors, including the immune status of the host, the infecting parasite species, or the parasite load at the lesion site. Understanding how these factors impact on the pathology of cutaneous leishmaniasis (CL) may provide new targets to manage the infection and improve clinical outcome. We quantified the relative expression of 170 genes involved in a diverse range of biological processes, in the skin biopsies from patients afflicted with CL caused by infection with either L. major or L. tropica. As compared to healthy skin, CL lesions bear elevated levels of transcripts involved in the immune response, and conversely, present a significant downregulation in the expression of genes involved in epidermal integrity and arginine or fatty acid metabolism. The expression of transcripts encoding for cytotoxic mediators and chemokines in lesions was inversely correlated with the expression of genes involved in epidermal integrity, suggesting that cytotoxicity is a major mediator of CL pathology. When comparing the transcriptional profiles of lesions caused by either L. major or L. tropica, we found them to be very similar, the later presenting an aggravated inflammatory/cytotoxic profile. Finally, we identified genes positively correlated with the parasite load in lesions. Among others, these included Th2 or regulatory cytokines, such as IL4 or IL10. Remarkably, a single gene among our dataset, encoding for tryptophan-2,3-deoxygenase (TDO), presented a negative correlation with the parasite load, suggesting that its expression may restrict parasite numbers in lesions. In agreement, treatment of macrophages infected with L. major in vitro with a TDO inhibitor led to an increase in parasite transcripts. Our work provides new insights into the factors that impact CL pathology and identifies TDO as a restriction factor for cutaneous Leishmania.

Non-human primates and Leishmania immunity

“…The administration of pentavalent antimonial sodium stibogluconate (20 mg/kg for 20 days) in infected macaques, reduced the lesion severity and accelerated healing, which was associated with the modulation in the expression of hundred genes in the skin biopsies from the lesion site [63] . These findings are in agreement with data from human biopsies, which demonstrated that treatment failure was linked to the excessive activation of the cytolytic pathway activated during infection [64] , [65] . Additional studies in macaques could also address the role of tryptophan-2,3-deoxygenase (TDO), that has recently been described to inhibit parasite burden in human lesions and cultured macrophages [65] .…”

Immunometabolism of Leishmania granulomas

“…Macrophages also utilize tryptophan for NAD + biosynthesis, with tryptophan 2,3‐dioxygenase (TDO) catalyzing the first step. Although TDO expression is not induced by IFNγ, TDO levels are negatively correlated with parasite load in L. major cutaneous lesions and TDO inhibition in ex vivo infected macrophages promotes parasite growth 49 . Whether indoleamine‐2,3‐dioxygenase and TDO act synergistically or separately to restrict Leishmania growth needs further investigation.…”

“…IFNc-activated M1 macrophages upregulate expression of indoleamine-2,3-dioxygenase and the conversion of tryptophan to kynurenine metabolites, reducing the availability of tryptophan to amastigotes. 49 Indoleamine-2,3-dioxygenase is highly expressed in cutaneous Leishmania lesions, although the impact of indoleamine-2,3-dioxygenase 1 expression on parasite burden remains poorly defined. Macrophages also utilize tryptophan for NAD + biosynthesis, with tryptophan 2,3-dioxygenase (TDO) catalyzing the first step.…”

“…Although TDO expression is not induced by IFNc, TDO levels are negatively correlated with parasite load in L. major cutaneous lesions and TDO inhibition in ex vivo infected macrophages promotes parasite growth. 49 Whether indoleamine-2,3-dioxygenase and TDO act synergistically or separately to restrict Leishmania growth needs further investigation. ) as a result of reverse electron transport in the respiratory chain and (iii) increased production of nitrous oxide (NO) from exogenous arginine or arginine produced via the argininosuccinate (AS) and mitochondrial aspartate/fumarate shunt.…”

“…Leishmania growth within macrophages may also be constrained by the availability of other amino acids, such as tryptophan. IFNγ‐activated M1 macrophages upregulate expression of indoleamine‐2,3‐dioxygenase and the conversion of tryptophan to kynurenine metabolites, reducing the availability of tryptophan to amastigotes 49 . Indoleamine‐2,3‐dioxygenase is highly expressed in cutaneous Leishmania lesions, although the impact of indoleamine‐2,3‐dioxygenase 1 expression on parasite burden remains poorly defined.…”