Unveiling Immune System Perturbations in Early Development Through Zebrafish Models of NADHX Repair Deficiency

Area of Science:

• Biochemistry
• Genetics
• Neuroscience

Background:

• NADH and NADPH are vital cofactors susceptible to hydration, forming inactive NADHX and NADPHX.
• Cellular repair enzymes NAD(P)HX dehydratase (NAXD) and NAD(P)HX epimerase (NAXE) are essential for metabolomic stability.
• Mutations in NAXD or NAXE lead to early-onset progressive encephalopathy (PEBEL), often triggered by fever and resulting in premature death.

Purpose of the Study:

• To investigate the disease mechanisms of PEBEL by creating and analyzing zebrafish models deficient in naxe or naxd.
• To explore potential therapeutic strategies for PEBEL disease.

Main Methods:

• CRISPR/Cas9 gene editing was used to generate zebrafish lines lacking functional naxe or naxd.
• Phenotypic analysis included locomotion assessment and survival rates.
• Gene expression analysis and neutral red staining were employed to evaluate immune cell activity.
• Nicotinic acid supplementation was tested as a potential therapeutic intervention.

Main Results:

• Both naxe-/- and naxd-/- zebrafish models accumulated NADHX.
• Only naxd-/- larvae exhibited a severe phenotype, characterized by reduced locomotion and early mortality.
• Nicotinic acid supplementation partially rescued the phenotype in naxd-/- larvae.
• Both mutant lines showed signs of immune system dysregulation, including altered gene expression and increased microglial activation.

Conclusions:

• Immune system perturbations are implicated in PEBEL disease pathogenesis, consistent with its inflammatory triggers in humans.
• The naxd-/- zebrafish model is a valuable tool for studying PEBEL disease mechanisms and for preclinical drug screening, particularly for agents like nicotinic acid.