Disruption of mitochondrial dynamics affects behaviour and lifespan in Caenorhabditis elegans

Abstract

Mitochondria are essential components of eukaryotic cells, carrying out critical physiological processes that include energy production and calcium buffering. Consequently, mitochondrial dysfunction is associated with a range of human diseases. Fundamental to their function is the ability to transition through fission and fusion states, which is regulated by several GTPases. Here, we have developed new methods for the non-subjective quantification of mitochondrial morphology in muscle and neuronal cells of Caenorhabditis elegans . Using these techniques, we uncover surprising tissue-specific differences in mitochondrial morphology when fusion or fission proteins are absent. From ultrastructural analysis, we reveal a novel role for the fusion protein FZO-1/mitofusin 2 in regulating the structure of the inner mitochondrial membrane. Moreover, we have determined the influence of the individual mitochondrial fission (DRP-1/DRP1) and fusion (FZO-1/mitofusin 1,2; EAT-3/OPA1) proteins on animal behaviour and lifespan. We show that loss of these mitochondrial fusion or fission regulators induced age-dependent and progressive deficits in animal movement, as well as in muscle and neuronal function. Our results reveal that disruption of fusion induces more profound defects than lack of fission on animal behaviour and tissue function, and imply that while fusion is required throughout life, fission is more important later in life likely to combat ageing-associated stressors. Furthermore, our data demonstrate that mitochondrial function is not strictly dependent on morphology, with no correlation found between morphological changes and behavioural defects. Surprisingly, we find that disruption of either mitochondrial fission or fusion significantly reduces median lifespan, but maximal lifespan is unchanged, demonstrating that mitochondrial dynamics play an important role in limiting variance in longevity across isogenic populations. Overall, our study provides important new insights into the central role of mitochondrial dynamics in maintaining organismal health. Electronic supplementary material The online version of this article (10.1007/s00018-019-03024-5) contains supplementary material, which is available to authorized users.

Causal roles of mitochondrial dynamics in longevity and healthy aging

“…A recent study investigating the effect of perturbing mitochondrial fission and fusion on C. elegans lifespan and health span showed that loss of fission decreased neuronal function and performance across several behavioral tests primarily during development (L4 stage) and in aged animals (day 7 and day 11 adults), but not during early adulthood (day 3 adults). Loss of fusion, however, produced more consistent and progressive neurological and behavioral defects all across development and adulthood (L4, day 3, day 7, and day 11 adults) [82]. Complementary findings from Rana et al showing lifespan extension in Drosophila only upon midlife induction of mitochondrial fission, not in early adulthood, and lifespan shortening with midlife upregulation of dMFN highlight that mitochondrial fission plays a key role in early development and around midlife [27].…”

“…Despite the requirement of fusion for lifespan‐extending interventions , most studies show that driving fusion or fission alone is not sufficient to increase lifespan and sometimes negatively affects health and longevity. Deletion of drp‐1 , fzo‐1 , or eat‐3 in C. elegans reduces median lifespan and induces motor and sensory impairments, yet pathologies associated with inhibiting one process can often be restored by inhibiting the other . Yeast cells deficient for fission and fusion ( dnm1 ; mgm1 double knockout, Table ) actually have healthy‐looking mitochondria with a wild‐type morphology, although these yeast do have a shortened lifespan .…”

Pluronic gel-based burrowing assay for rapid assessment of neuromuscular health inC. elegans

“…Even though burrowing of nematodes in soil-like environments has been previously studied [48][49][50], only recently has it been used for evaluation of neuromuscular health in C. elegans [16,18,19,22,51]. These recent investigations employed agar as a medium for burrowing.…”

“…Since the original method was conceived [18], it has been applied to score muscular dystrophy mutants [16], and to probe calcium dysregulation and longevity outcomes due to physical exertion in the burrowing environment in these mutants [19]. Additionally, a burrowing assay has been used to assess mutants with defects in mitochondrial fission and fusion proteins [22]. Here, we have developed an improved burrowing method based on a thermoreversible Pluronic gel and expanded its application to diverse areas with novel findings.…”

“…Burrowing capacity has been examined in agar-filled pipettes by stimulating animals to move towards the food source present at one end of the pipette [16,18,22]. A limitation of this burrowing assay is that the methodology requires time-consuming steps including drilling holes in the pipette (later used for loading animals and food source), followed by filling the pipettes uniformly with hot agar and waiting for them to cool.…”