Unique Properties of Apicomplexan Mitochondria.

Apicomplexan parasites constitute more than 6,000 species infecting a wide range of hosts. These include important pathogens such as those causing malaria and toxoplasmosis. Their evolutionary emergence coincided with the dawn of animals. Mitochondrial genomes of apicomplexan parasites have undergone dramatic reduction in their coding capacity, with genes for only three proteins and ribosomal RNA genes present in scrambled fragments originating from both strands. Different branches of the apicomplexans have undergone rearrangements of these genes, with Toxoplasma having massive variations in gene arrangements spread over multiple copies. The vast evolutionary distance between the parasite and the host mitochondria has been exploited for the development of antiparasitic drugs, especially those used to treat malaria, wherein inhibition of the parasite mitochondrial respiratory chain is selectively targeted with little toxicity to the host mitochondria. We describe additional unique characteristics of the parasite mitochondria that are being investigated and provide greater insights into these deep-branching eukaryotic pathogens.

Mitochondrially targeted proximity biotinylation and proteomic analysis in Plasmodium falciparum.

Despite ongoing efforts to control malaria infection, progress in lowering the number of deaths and infections appears to have stalled. The continued high incidence of malaria infection and mortality is in part due to emergence of parasites resistant to frontline antimalarials. This highlights the need for continued identification of novel protein drug targets. Mitochondrial functions in Plasmodium falciparum, the deadliest species of human malaria parasite, are targets of validated antimalarials including atovaquone and proguanil (Malarone). Thus, there has been great interest in identifying other essential mitochondrial proteins as candidates for novel drug targets. Garnering an increased understanding of the proteomic landscape inside the P. falciparum mitochondrion will also allow us to learn about the basic biology housed within this unique organelle. We employed a proximity biotinylation technique and mass spectrometry to identify novel P. falciparum proteins putatively targeted to the mitochondrion. We fused the leader sequence of a mitochondrially targeted chaperone, Hsp60, to the promiscuous biotin ligase TurboID. Through these experiments, we generated a list of 122 "putative mitochondrial" proteins. To verify whether these proteins were indeed mitochondrial, we chose five candidate proteins of interest for localization studies using ectopic expression and tagging of each full-length protein. This allowed us to localize four candidate proteins of unknown function to the mitochondrion, three of which have previously been assessed to be essential. We suggest that phenotypic characterization of these and other proteins from this list of 122 could be fruitful in understanding the basic mitochondrial biology of these parasites and aid antimalarial drug discovery efforts.

Regulatory IgDhi B Cells Suppress T Cell Function via IL-10 and PD-L1 during Progressive Visceral Leishmaniasis.

During visceral leishmaniasis (VL), Th1-based inflammation is induced to control intracellular parasites. Inflammation-based pathology was shown to be dampened by IL-10 and eventual programmed death 1-mediated T cell exhaustion. Cell type(s) responsible for the initiation of T cell-produced IL-10 during VL are unknown. CD19(+), CD5(-), CD1d(-), IgD(hi) regulatory B cells from healthy controls produced IL-10 in the absence of infection or stimulation, in contrast to IgD(lo/neg) B cells. IgD(hi) B cells may have a de novo versus induced regulatory program. The population of IgD(hi) B cells increased 3-fold as VL progressed. B cells from VL dogs were necessary and sufficient to suppress Th1 cell effector function. IgD(hi) B cells induced IL-10 production by T cells and IgD(lo) B cells. Blockage of B cell-specific PD-L1 restored Th1 responses. IgD(hi) regulatory B cells represent a novel regulatory B cell that may precipitate T cell exhaustion during VL.

Activation of autophagy and nucleotide-binding domain leucine-rich repeat-containing-like receptor family, pyrin domain-containing 3 inflammasome during Leishmania infantum-associated glomerulonephritis.

Chronic kidney disease is a major contributor to human and companion animal morbidity and mortality. Renal complications are sequelae of canine and human visceral leishmaniasis (VL). Despite the high incidence of infection-mediated glomerulonephritis, little is known about pathogenesis of VL-associated renal disease. Leishmania infantum-infected dogs are a naturally occurring model of VL-associated glomerulonephritis. Membranoproliferative glomerulonephritis type I [24 of 25 (96%)], with interstitial lymphoplasmacytic nephritis [23 of 25 (92%)], and glomerular and interstitial fibrosis [12 of 25 (48%)] were predominant lesions. An ultrastructural evaluation of glomeruli from animals with VL identified mesangial cell proliferation and interposition. Immunohistochemistry demonstrated significant Leishmania antigen, IgG, and C3b deposition in VL dog glomeruli. Asymptomatic and symptomatic dogs had increased glomerular nucleotide-binding domain leucine-rich repeat-containing-like receptor family, pyrin domain containing 3 and autophagosome-associated microtubule-associated protein 1 light chain 3 associated with glomerular lesion severity. Transcriptional analyses from symptomatic dogs confirmed induction of autophagy and inflammasome genes within glomeruli and tubules. On the basis of temporal VL staging, glomerulonephritis was initiated by IgG and complement deposition. This deposition preceded presence of nucleotide-binding domain leucine-rich repeat-containing-like receptor family, pyrin domain containing 3-associated inflammasomes and increased light chain 3 puncta indicative of autophagosomes in glomeruli from dogs with clinical VL and renal failure. These findings indicate potential roles for inflammasome complexes in glomerular damage during VL and autophagy in ensuing cellular responses.