APOLs with low pH dependence can kill all African trypanosomes

Area of Science:

• Immunology
• Parasitology
• Biochemistry

Background:

• Apolipoprotein L1 (APOL1) is a primate-specific serum protein and the sole secreted member of a protein family that promotes cell death.
• APOL1 exhibits trypanolytic activity against Trypanosoma brucei brucei but not against human-infecting subspecies like T.b. rhodesiense and T.b. gambiense.
• The study explored the potential of intracellular APOL1 family members to target pathogenic African trypanosomes, which may not have evolved resistance mechanisms against them.

Purpose of the Study:

• To investigate the trypanolytic activity of APOL3 against various African trypanosome species.
• To compare the trypanolytic efficacy of APOL3 and APOL1, and to understand the role of pH in their activity.
• To assess the therapeutic potential of APOL1 family members, including modified variants, against trypanosomiasis.

Main Methods:

• Recombinant proteins APOL3 and APOL1 (including a modified rPpAPOL1 mutant) were synthesized and tested for trypanolytic activity in vitro.
• The activity of these proteins against different trypanosome species, including T.b. rhodesiense, T.b. gambiense, T. evansi, T. congolense, T. vivax, T. theileri, and T. cruzi, was evaluated.
• The influence of acidic pH on the trypanolytic activity of APOL3 and APOL1 was assessed.
• The efficacy of an experimental rPpAPOL1 mutant in inhibiting T.b. gambiense infection in a mouse model was determined.

Main Results:

• Recombinant APOL3 (rAPOL3) demonstrated trypanolytic activity against all tested African trypanosomes, including pathogenic human subspecies and animal pathogens.
• rAPOL3's trypanolytic effect was specific, as it did not kill more distantly related trypanosomes like T. theileri or T. cruzi.
• The trypanolytic potential of rAPOL3 and rAPOL1 was partially shared, with differential activity linked to pH dependence.
• An experimental rPpAPOL1 mutant, inspired by APOL3, showed enhanced in vitro trypanolytic activity and completely inhibited T.b. gambiense infection in mice.

Conclusions:

• APOL3 exhibits broad-spectrum trypanolytic activity against African trypanosomes, suggesting potential for therapeutic development.
• pH dependence is a critical factor influencing the trypanolytic efficacy of APOL1 family proteins.
• A modified APOL1 variant demonstrates significant therapeutic promise for treating African trypanosomiasis, as evidenced by in vitro and in vivo efficacy.