Study The Effect And Cellular Mechanism Of Long-term Every-other-day Fasting On Memory Impairment In Aged Mice

Aging refers to gradual decline of body structure and function,as individuals are getting old.Aged individuals are often symptomized by moderate or severe memory impairment.Currently,aging population is being seriously increased,how to improve cognitive impairment associated with aging has become a big challenge faced by today’s society.Every other day fasting(EOD)refers to a dietary restriction measure that alternates between eating freely for 24 hours and no calories intake for 24 hours.Studies have demonstrated that EOD regulates energy metabolism,reduces systemic inflammation,promotes neurogenesis,increases brain plasticity,improves learning and memory,and slows down aging process.However,there is still a lack of relevant reports on whether long-term EOD can improve memory impairment associated with aging.Objective:To investigate the effect and cellular mechanism of long-term EOD on age-related memory impairments.Method:We used behavioral paradigms to evaluate the impact of long-term EOD(6months and above)on learning and memory in aged(18-24 months old)male mice.We investigated the effect of long-term EOD on brain activity of behavioral mice with in vivo EEG recording.The effect of long-term EOD on synaptic plasticity of hippocampal neurons in aged mice was evaluated by ex vivo field excitatory postsynaptic potential(f EPSP)recordings We tested the effect of long-term EOD on neuronal excitability of aged mice with ex vivo whole-cell patch-clamp recordings in hippocampal slices.The protein chips are used to assay the effect of long-term EOD on inflammation-related protein expression in the hippocampus of aged mice.Live imaging technique was used to observe the effect of long-term EOD on visceral and subcutaneous fat distribution in aged mice.Hematoxylin eosin(HE)staining was used to investigate the effects of long-term EOD on peripheral(adipose and liver tissues)and central(prefrontal cortex)inflammation in aged mice.The effect of long-term EOD on peripheral blood components was measured with blood component analyzer in aged mice.Result:1.Open field(OF)and elevated plus maze(EPM)tests showed that long-term EOD did not affect spontaneous activity and baseline anxiety of aged mice.However,aged mice with long-term EOD exhibited better memories than age-matched control mice in new object recognition(NOR),object-place recognition(OPR),social recognition(SR),and Morris water maze tests,indicating that long-term EOD improved aging-associated memory impairments.In addition,rotarod tests showed that long-term EOD improved motor learning and memory in aged mice.2.In vivo EEG recordings indicated that long-term EOD enhanced neuronal activity of the prefrontal cortex and increased proportion of α wave during social memory retrieval in aged mice.3.Hippocampal f EPSPs recordings revealed that long-term EOD significantly enhanced long-term potentiation(LTP)in hippocampal SC-CA1 pathway of aged mice.4.Whole-cell patch-clamp recordings ex vivo showed that long-term EOD increased neuronal excitability of hippocampal pyramidal neurons in aged mice.The absolute value of afterhyperpolarization potential(AHP)of pyramidal neurons was reduced in EOD mice,without changes in resting potential or threshold potential.5.Transmission electron microscope results showed that the excitatory postsynaptic density in the hippocampus of long-term EOD mice was enlarged.6.Protein chips analyses revealed that long-term EOD down-regulated expression of inflammation-related proteins in the hippocampus of aged mice.7.In vivo imaging study showed that long-term EOD reduced visceral and subcutaneous fat distribution,meanwhile increased brown adipose tissue in aged mice.8.HE staining indicated that long-term EOD reduced the number of macrophages around blood vessels in the prefrontal cortex and liver tissue of aged mice.9.Peripheral blood cell composition assays showed that long-term EOD reduced peripheral white blood cells(monocytes,macrophages,etc.)in aged mice,but did not affect red blood cells.In conclusion,our study had demonstrated that long-term EOD facilitates excitability and synaptic plasticity of pyramidal neurons in the hippocampus,increases α wave ratio closely related to learning and memory process in the prefrontal cortex,thus contributing to improved memory in aged mice.In addition,our study reveals that long-term EOD reduces central and peripheral inflammation in aged mice,suggesting that the EOD-induced improvement of memory and neuronal function in aged mice may closely associate with its anti-inflammatory effects.Further studies are still required to elucidate the cellular and molecular mechanisms underlying the beneficial effect of long-term EOD on aging-related inflammation and memory impairments.Conclusion:Long-term EOD suppresses aging-related systemic inflammation and improves aging-related memory impairments.Therefore,EOD may become an effective,durable dietary restriction strategy to combat age-related cognitive impairment.It is worth noting that,long-term EOD reduces white blood cells in aged mice,suggesting that it may have adverse effect on immune function,which should be taken account.