Biology subjects

Votborg-Novel, L.

Publications and source records attributed to Votborg-Novel, L..

4 recordsLinked to original sources

bioRxiv2025

Seasonal transcriptional profiling of malaria parasites using a new single-cell atlas of a Malian Plasmodium falciparum isolate

Asymptomatic persistence is crucial for the survival of malaria parasites in seasonal transmission settings, where transmission halts during dry months, while mosquitos are scarce and new infections rare. How Plasmodium falciparum avoids causing host symptoms or being cleared is not fully understood. Parasites that persist through the dry season circulate longer within the [~]48h replication cycle compared to parasites isolated from clinical cases, where only early stages circulate. The mechanisms promoting increased circulation and avirulent infections bridging two wet seasons remain unclear. We generated a single-cell RNA-seq reference atlas with P. falciparum erythrocytic stages of a recently adapted isolate, and with it defined the developmental stage of over 25000 parasites from six asymptomatic children at the dry-wet season transition, and nine children with clinical malaria in the wet season. Our data confirms that older parasites circulate in the dry season, and reveals transcriptional modulation of exported proteins that affect cytoadhesion of infected erythrocytes, which we validated by immuno-fluorescence microscopy.

molecular biology↗

bioRxiv2025

A Metabolite-Based Resistance Mechanism Against Malaria

Whether jaundice, a common presentation of Plasmodium (P.) falciparum malaria (1-3) arising from the accumulation of circulating bilirubin, represents an adaptive or maladaptive response to Plasmodium spp. infection is not understood (1-3). We found that asymptomatic P. falciparum infection was associated with a >10-fold higher ratio of unconjugated bilirubin over parasite burden, compared to symptomatic malaria. Genetic suppression of bilirubin synthesis by biliverdin reductase A (BVRA) (4) increased parasite virulence and malaria mortality in mice. Accumulation of unconjugated bilirubin in plasma, via genetic inhibition of hepatic conjugation by UDP glucuronosyltransferase family 1 member A1 (UGT1A1) (5), was protective against malaria in mice. Unconjugated bilirubin inhibited P. falciparum proliferation in red blood cells (RBC) via a mechanism that suppressed mitochondrial pyrimidine synthesis. Moreover, unconjugated bilirubin inhibited hemozoin (Hz) crystallization and compromised the parasites food vacuole. In conclusion, jaundice represents a metabolic response to Plasmodium spp. infection that limits malaria severity.

immunology↗

bioRxiv2024

Plasmodium falciparum expresses fewer var genes at lower levels during asymptomatic dry season infections than clinical malaria cases

In seasonal transmission areas, clinical malaria occurs during the wet season when mosquitoes are present, while in the dry season, malaria transmission is interrupted and clinical cases are rare. In Mali, Plasmodium falciparum can persist in low parasitaemic asymptomatic individuals through the six-month dry season and shows reduced cytoadhesion of infected erythrocytes, evidenced by the circulation of further developed parasite stages compared to clinical malaria cases. How prolonged circulation of infected erythrocytes is achieved remains unknown. Here, we explored var gene expression in subclinical infections and clinical malaria cases of Malian children, collected during the dry and wet seasons. We sequenced expressed var DBL-tags, used bioinformatic tools to predict their domain composition, binding phenotype and upstream sequence type; and determined their relationship to seasonality and clinical presentation. We found that parasites of asymptomatic infections expressed fewer var genes, with a larger proportion of var transcripts attributed to one or a few vars. In contrast, clinical cases exhibited expression of many var genes at lower proportions. We found that parasites of asymptomatic carriers expressed a mixture of CD36- and EPCR-binding PfEMP1, which changed over time. We confirmed that vars encoding CD36-binding PfEMP1 dominated in non-severe malaria cases, and found no significant difference in expressed var types between dry and wet seasons. Asymptomatic carriers were older, had higher titers of anti-P. falciparum antibodies, and broader reactivity to PfEMP1, suggesting that host immunity was the main determinant limiting var transcript variation in asymptomatic carriers. However, by RNAseq and qRT-PCR we also observed significantly higher total var transcript levels in malaria cases compared to asymptomatic carriers, suggesting that in addition to the parasites switching and the hosts immune selection of expressed var genes, parasites able to sustain long-term infections may be poised for reduced PfEMP1 expression.

microbiology↗

bioRxiv2024

Iron transport pathways in the human malaria parasite Plasmodium falciparum revealed by RNA-sequencing

Host iron deficiency is protective against severe malaria as the human malaria parasite Plasmodium falciparum depends on bioavailable iron from its host to proliferate. The essential pathways of iron acquisition, storage, export, and detoxification in the parasite differ from those in humans, as orthologs of the mammalian transferrin receptor, ferritin, or ferroportin, and a functional heme oxygenase are absent in P. falciparum. Thus, the proteins involved in these processes may be excellent targets for therapeutic development, yet remain largely unknown. Here, we show that parasites cultured in erythrocytes from an iron-deficient donor displayed significantly reduced growth rates compared to those grown in red blood cells from healthy controls. Sequencing of parasite RNA revealed diminished expression of genes involved in overall metabolism, hemoglobin digestion, and metabolite transport under low-iron versus control conditions. Supplementation with hepcidin, a specific ferroportin inhibitor, resulted in increased labile iron levels in erythrocytes, enhanced parasite replication, and transcriptional upregulation of genes responsible for merozoite motility and host cell invasion. Through endogenous GFP tagging of differentially expressed putative transporter genes followed by confocal live-cell imaging, proliferation assays with knockout and knockdown lines, and protein structure predictions, we identified six proteins that are likely required for ferrous iron transport in P. falciparum. Of these, we localized PfVIT and PfZIPCO to cytoplasmic vesicles, PfMRS3 to the mitochondrion, and the novel putative iron transporter PfE140 to the plasma membrane for the first time in P. falciparum. PfNRAMP/PfDMT1 and PfCRT were previously reported to efflux Fe2+ from the digestive vacuole. Our data support a new model for parasite iron homeostasis, in which PfE140 is involved in iron uptake across the plasma membrane, PfMRS3 ensures non-redundant Fe2+ supply to the mitochondrion as the main site of iron utilization, PfVIT transports excess iron into cytoplasmic vesicles, and PfZIPCO exports Fe2+ from these organelles in case of iron scarcity. These results provide new insights into the parasites response to differential iron availability in its environment and into the mechanisms of iron transport in P. falciparum as promising candidate targets for future antimalarial drugs.

cell biology↗