Age-related changes at the Caenorhabditis elegans neuromuscular junction

Abstract

The ageing population is an important problem for society as it predisposes individuals towards disease. Cognitive decline, dementia and frailty are associated with ageing, and much evidence supports a central role of synapses. However, the mechanisms by which aged synapses are compromised remain unclear. This thesis describes a functional analysis of the C. elegans neuromuscular system across ageing to model the effects of ageing on synaptic physiology. Motility assays were used to give an insight into the integrity of the neuromuscular system. Aldicarb and levamisole-induced whole worm contraction assays were used to give a more detailed insight into the integrity of presynaptic and postsynaptic loci. Patch clamp analysis of miniature postsynaptic currents (mPSCs) was used to characterise neurotransmission across ageing. Lastly, different genetic backgrounds were used to investigate the contribution of longevity and synaptic pathways to NMJ function across age. C. elegans has a median lifespan of 14 17 days and becomes progressively immotile with age, with swimming frequency decreasing from 110±3 to 71±12 beats per minute from day 1 to day 5 of adulthood. Counter intuitively, this was coincident with an increase in NMJ efficacy identified using aldicarb and levamisole contraction assays. Patch clamp analysis of neuromuscular transmission also revealed increased mPSC frequency and amplitude from 9±3 to 33±7 Hz and 15±1 to 27±4 pA between day 1 and 5 of adulthood. As animals progress from early ageing to later ages on day 10 and 16 of adulthood, NMJ efficacy decreases, but not to levels lower than that seen on day 1 of adulthood. Patch clamp analysis revealed increased in mPSC frequency and amplitude from 9±3 to 22±9 Hz and 15±1 to 19±4 pA between day 1 and 10 of adulthood, indicating more neurotransmitter release and preserved sensitivity in aged, immotile worms. The contraction assays indicate that even very aged, immotile worms on day 16 of adulthood had functional muscle cells. daf-2(e1370) worms have reduced insulin signalling and show extended lifespan and motility across ageing. Aldicarb assays in daf- 2 worms indicate insulin signalling is required for increased neurotransmitter release during early ageing. dnj-1 (tm3223) worms lack the homologue of a synaptic co chaperone, CSP. Lifespan, swimming, contraction and patch clamp analysis of neuromuscular function in dnj-14 worms revealed no defects compared to wild type across lifespan. In summary, there is an increase in NMJ efficacy during early ageing that is dependent on insulin signalling, a conserved longevity and synaptic physiology regulator. During later ageing, C.elegans NMJs remain functional. In contrast to conclusions from previous morphological studies, muscle function is largely preserved across the C. elegans lifespan, indicating additional determinates including the motor circuit may play a role in age-related immotility. This study resonates with emerging evidence in mammalian systems that defective signalling in neuronal circuits is a key mechanism for age-related impairment of the nervous system, in which changes in synaptic function may play a role.

More information

Identifiers

ORCID for Vincent O'Connor: orcid.org/0000-0003-3185-5709

ORCID for Lindy M.. Holden-Dye: orcid.org/0000-0002-9704-1217

Catalogue record

Export record