Zebrafish models of PEBEL 1 & 2 neurometabolic disorder reveal that impairments of immune system participate in disease manifestation#

Authors#

Myrto Patraskaki, Ursula Heins-Marroquin, Najmesadat Seyedkatouli, Maria Lorena Cordero Maldonado, Carole Linster

Abstract#

NADH and NADPH are essential cofactors that are prone in vivo to hydration, producing damaged hydroxylated redox-inactive derivatives (designated NADHX and NADPHX). These damaged metabolites can be converted back to their active forms by a specialized metabolite repair system, which consists of two highly conserved partner enzymes, an ATP-dependent NAD(P)HX dehydratase (NAXD) and an NAD(P)HX epimerase (NAXE). Mutations in either one of these genes cause a progressive encephalopathy with brain edema and/or leukoencephalopathy (PEBEL) that seems to be triggered by fever or inflammation. These pediatric neurodegenerative disorders are characterized by ataxia, muscular hypotonia, respiratory insufficiency and/or respiratory failure, skin manifestations, and finally, premature death. In the present study, we generated the first naxd- and naxe-deficient zebrafish lines using CRISPR/Cas9 technology to understand how the accumulation of NAD(P)HX and/or the depletion of NAD(P)H affect developmental processes that may lead eventually to neurodegeneration. Interestingly, although both models showed accumulation of the damaged metabolites, naxe-/- larvae did not present decreased survival and displayed milder phenotypes such as an increased number of microglial cells and an unexpectedly weaker inflammatory response to LPS treatment compared to control larvae. Similar to naxe-/-, naxd-/- zebrafish larvae showed increased number of microglia but without obvious phenotypes at very early developmental stages. However, after 10 dpf, naxd-/- larvae started manifesting decreased locomotion behavior, an increased inflammatory state, decreased numbers of microglia and macrophage markers, and early lethality. The fact that in humans, symptoms are triggered only upon inflammation or recurrent viral infections, indicates that the immune system might play a pivotal role in the disease development and our models provide interesting clues in that direction for this rare and fatal group of disorders.