Motor Dysfunction And The Related Neuroimmunologic Abnormality In 5xFAD Transgenic Mice

Object Alzheimer's disease(AD)is characterized by cognitive impairment,but it also has many non-cognitive disorders,for example,motor and sensory dysfunction.Notablely,motor dysfunction has caused wide attention.However,the order motor abnormality and non-cognitive symptom appears and the underlying mechanism remains unclear.This research was to investigate the phenotypic and temporal distribution of motor dysfunction in 5xFAD mice and to elucidate the mechanism caused by neuroimmune abnormality.Methods To elucidate the phenotypic characteristics of the motor behavior in 5xFAD and WT mice at 3,8 and 12-month,grip strength,muscle tension and the ability to keep balance and coordination were tested by means of grip strength test,hind limb extension and rotarod test,respectively.Immunofluorescence and confocal microscopy combined with Image J software were used to analyze and assess the activation of microglia and astrocytes and the relationship with A? deposition in motor cortex,striatum and spinal cord.We used western blot to quantify the expression of APP protein in spinal cord.Immune cytokine receptor Csf1 r,complement component C1 qa and brain-derived neurotrophic factor(BDNF)in spinal cord were measured by real-time quantitative PCR(qRT-PCR).The mechanism of motor dysfunction of 5xFAD transgenic mice was studyed from the aspects of neuropathology and neurochemistry.Result 1.Motor balance and coordination dysfunction appeared before the cognitive decline while weaker grip strength and dystonia showed up after cognitive abnormality.(1)Latency to fall was decreased in 3-month 5xFAD mice at the speed of 40 rpm in the rotarod test(p<0.01),suggesting motor balance and coordination disability in the early stage of AD.With the age increase,this phenomenon is more obvious in 8 and 12-month 5xFAD mice.(2)Grip strength of the four limbs began to fall in 8-month 5xFAD mice.(p< 0.0001)(3)Hind limb extension test is an important indicator of muscle tension,12-month 5xFAD transgenic mice can not stretch their hind limbs.The available evidence suggests that 5xFAD transgenic mice have decreased learning and memory ability at the age of 5-6 months.Based on all these results,it was strongly suggested that 5xFAD transgenic mice had a balance and coordination dysfunction before cognitive decline,and weaker strength of the four limbs and dystonia were observed after cognitive impairment.2.Immunohistochemical staining showed that microglia in the striatum was activated in 3-month 5xFAD mice.In spinal cord,they had higher tendency of activation,but the difference was not significant.Earlier 5xFAD mice showed decreased density of TH+ neurofibers(P < 0.001),but counts of ChAT-positive cells had no change in striatum.With the increase in age,8 and 12-months 5xFAD mice showed significant microglia activation and astrogliosis and a large number of A? deposition in motor cortex and spinal.Western blot showed that the expression of APP-the precursor protein of A? was increased in spinal cord of 8 and 12 months old 5xFAD mice.qRT-PCR showed that the expression of C1 qa and Csf1 r,chemokine receptor P2X7 and BDNF were increased in 8 and 12-month 5xFAD mice.There is no significant upregulation of TNF?,IL-1?.The results suggest that 5xFAD transgenic mice have neuropathic pathological abnormalities in CNS that are related to microglia and complement activation,chemotactic signaling abnormality.Conclusion 5xFAD transgenic mice had motor dysfunctions,among which decreased muscle strength and dystonia occurred in the late stage of the disease,but the balance and coordination dysfunction appeared earlier in AD,which is significantly earlier than the cognitive decline.The abnormal phenotype of 5xFAD transgenic mice was associated with dysplasia of motor cortex,striatum,microglia and astrocytes in the spinal cord and A?-mediated neuroimmune hyperactivity.The balance and coordination dysfunction appeared before AD cognitive impairment and are expected to be used to identify AD as a warning signal.The development of targeted drugs for the mechanism of neuroimmune abnormalities is conducive to delay the emergence of motor dysfunction and improve the quality of life of AD patients.