Feeding difficulties, a key feature of the Drosophila NDUFS4 mitochondrial disease model

Abstract

Mitochondrial diseases are associated with a wide variety of clinical symptoms and variable degrees of severity. Patients with such diseases generally have a poor prognosis and often an early fatal disease outcome. With an incidence of 1 in 5000 live births and no curative treatments available, relevant animal models to evaluate new therapeutic regimes for mitochondrial diseases are urgently needed. By knocking down ND-18, the unique Drosophila ortholog of NDUFS4, an accessory subunit of the NADH:ubiquinone oxidoreductase (Complex I), we developed and characterized several dNDUFS4 models that recapitulate key features of mitochondrial disease. Like in humans, the dNDUFS4 KD flies display severe feeding difficulties, an aspect of mitochondrial disorders that has so far been largely ignored in animal models. The impact of this finding, and an approach to overcome it, will be discussed in the context of interpreting disease model characterization and intervention studies.This article has an associated First Person interview with the first author of the paper.

A Drosophila Mitochondrial Complex I Deficiency Phenotype Array

“…In patients, mutations in subunits of complex I can cause isolated or combined OxPhos enzymatic activity disturbances. To determine whether knocking down of Drosophila CI subunits leads to comparable defects, we measured the activity of the five OxPhos complexes in the adult KD models and compared these to the complex activities of their isogenic controls and to previous data obtained for the S4 subunit (Foriel et al, 2018). Without any exception, all models that were sufficiently viable to allow collection of adult progenies presented a strong reduction of CI activity.…”

“…Other complexes activities were either significantly increased (CII in S7/Actin/25°C, CIII in all models, CIV in S7/Actin/25°C and S7/da/25°C) or significantly decreased (CV in S4/Actin/25°C). The numerical values are provided in Supplementary Table S1 (S4/actin/28°C graph reproduced/adapted with permission from Foriel et al, 2018).…”

“…Since defective mitochondria might lead to energy storage defects, we evaluated the percentage of eclosed flies by counting the empty and total number of pupae. Based on our previous work characterizing the S4/actin/28°C model (Foriel et al, 2018), we asked whether eclosion is also affected in S7, V1, and other S4 models. Our collection of CI-deficient models showed a wide range of eclosion rates, which can be classified in four groups (Figure 2): (1) no eclosion impairment such as S4/da/25°C with 93.7% of the flies eclosing compared to 97.1% for its control KK/da/25°C, (2) a modest impairment with S4/actin/25°C and S4/actin/28°C with, respectively, 68.9 and 36.9% of eclosed pupae in comparison to their respective control: control KK/actin/25°C (95.0%) and control KK/actin/28°C (95%), (3) a severe impairment with S4/da/28°C, S7/actin/25°C, S7/da/25°C for which eclosion rates were 16.3, 19.1, and 11.5%, respectively [significant for all of them in comparison to their respective controls: control KK/da/28°C (97.5%), control KK/actin/25°C (95%), and control KK/da/25°C (97.1%)], and (4) very severe eclosion defects with S7/actin/28°C, S7/da/28°C, V1/actin-da/25–28°C, having eclosion rates below 2% and lethality at larval (L1, L2, and L3) and pupal stages.…”

“…These validated the hairpin integrations at position 30B on chromosome 2L, and excluded a hairpin integration at position 40D that can be associated with dominant off-target phenotypes (Green et al, 2014; Vissers et al, 2016). S4/actin/28°C KD and phenotypes have previously been published (Foriel et al, 2018) and were reproduced/adapted with the permission from Disease Models and Mechanisms (DMM). In Drosophila , NDUFS7 and NDUFV1 have several orthologs (S7: ND-20 and ND-20L; V1: ND-51, ND-51L1, and ND-51L2).…”

Defined neuronal populations drive fatal phenotype in Leigh Syndrome

“…In contrast, Vglut2:Ndufs4cKO and Gad2:Ndufs4cKO mice had reduced lifespan and body weight, which was accompanied by a decrease in food intake, which are common clinical signs that appear in Leigh Syndrome patients 1,30 . Recent reports have shown that neuronal cell-specific NDUFS4 knock down in Drosophila also leads to severe feeding abnormalities and premature death 31 . Our results indicate a conserved role for neurons in the onset and progression of the pathological condition of global Ndufs4 deficiency and reveal that both glutamatergic and GABAergic systems contribute to the growth and lethality phenotype.…”