The Role of Modified UNC-68 in Age-related Caenorhabditis elegans Muscle Function Loss

Age-dependent loss of body wall muscle function and locomotion has been observed in C. elegans, however its cause has yet to be elucidated. Utilizing biochemical techniques and calcium imaging, we demonstrate that aberrant calcium (Ca2+) release via the ryanodine receptor (RyR) homologue UNC-68 contributes to age-dependent muscle weakness in C. elegans. We show that UNC-68 comprises a macromolecular complex bearing FKB-2, a C. elegans immunophilin with high homology to the stabilizing subunit calstabin (calcium channel stabilizing binding protein, or FKBP12). Furthermore, we demonstrate that as the nematode ages, UNC-68 is oxidized and depleted of FKB-2, resulting in “leaky” channels, depleted SR calcium stores, and a reduction in body wall muscle Ca2+ transients at baseline. These perturbations resulted in a motility phenotype, where fkb-2(ok3007) worms harboring a deletion mutation that abolishes FKB-2 binding to the UNC-68 macromolecular complex suffered from poor muscle performance and exercise fatigue in swimming trials. Moreover, pharmacological interventions inducing oxidization of UNC-68 and depletion FKB-2 from the channel independently cause reduced body wall muscle Ca2+ transients, strongly suggesting that UNC-68 oxidation and FKB-2 depletion contribute to muscle function loss observed in aging. UNC-68 oxidation was found to correlate with lifespan, happening earlier in short-lived mitochondrial electron transport chain strains and later in long-lived worms. Finally, preventing FKB-2 depletion from the UNC-68 macromolecular complex in aged C. elegans using the Rycal drug S107 improved muscle Ca2+ transients. Taken together, our data implicate UNC-68 dysfunction in the underlying mechanism of muscle function loss in C. elegans, analogous to observations made of RyR1 dysfunction in aged mammalian skeletal muscle, and describes for the first time a potential role for FKB-2 in C.elegans physiology.