Friday, August 30, 2019

Loss of control in aging cells.

Wow...experiments like those of Pereda et al. make me feel rather fatalistic and resigned to the aging process, notwithstanding all the numerous pie in the sky biotech startups that are trying to find magic bullets that will reverse human aging. They note that deterioration in learning and memory with aging is not accompanied by obvious increases in nerve cell death, and so looked for more subtle changes that might be a play. They created transgenic mice that expressed a calcium sensor specifically in presynaptic terminals of the CA1 region of the hippocampus, allowing them to measure how calcium signaling altered with age. Older animals showed increased calcium influx into the neurons and persistently increased concentration of calcium in resting neurons, most likely caused by by an age‐dependent change in the properties or numbers of presynaptic calcium channels. Higher calcium altered neuronal transmission with parallel loss of cognitive function in the animals. Interestingly, reducing extracellular calcium made old synapses behave more like younger ones, and raising extracellular calcium made young synapses act like old ones.  Here is their technical abstract:
The loss of cognitive function accompanying healthy aging is not associated with extensive or characteristic patterns of cell death, suggesting it is caused by more subtle changes in synaptic properties. In the hippocampal CA1 region, long‐term potentiation requires stronger stimulation for induction in aged rats and mice and long‐term depression becomes more prevalent. An age‐dependent impairment of postsynaptic calcium homeostasis may underpin these effects. We have examined changes in presynaptic calcium signalling in aged mice using a transgenic mouse line (SyG37) that expresses a genetically encoded calcium sensor in presynaptic terminals. SyG37 mice showed an age‐dependent decline in cognitive abilities in behavioural tasks that require hippocampal processing including the Barnes maze, T‐maze and object location but not recognition tests. The incidence of LTP was significantly impaired in animals over 18 months of age. These effects of aging were accompanied by a persistent increase in resting presynaptic calcium, an increase in the presynaptic calcium signal following Schaffer collateral fibre stimulation, an increase in postsynaptic fEPSP slope and a reduction in paired‐pulse facilitation. These effects were not caused by synapse proliferation and were of presynaptic origin since they were evident in single presynaptic boutons. Aged synapses behaved like younger ones when the extracellular calcium concentration was reduced. Raising extracellular calcium had little effect on aged synapses but altered the properties of young synapses into those of their aged counterparts. These effects can be readily explained by an age‐dependent change in the properties or numbers of presynaptic calcium channels.

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