Researsh On The Mechanism Of Kalirin-7 Regulating Neuronal Plasticity

Neuroplasticity is the modifiability of the central nervous system in structural and functional activities,including spine plasticity,synaptic plasticity,neurogenesis,synaptic regeneration,neural network reorganization and functional brain areas metastasis,and is a hot topic of neurobiology nowadays.Neuroplasticity is the critical mechanism of nervous system involving structural and functional adaptations underlying the influence of environment.Meanwhile,neuroplasticity also is the neurobiological base of normal physiological process including learning and memory.Furthermore,neuroplasticity is closely related to various pathophysiological processes,including drug addiction,depression,schizophrenia,alzheimer’s disease and autism.Therefore,an in-depth study of neuroplasticity mechanism is of the utmost importance in treating related mental and neurological diseases.Neural networks consisting of synaptic connections play central roles in physiological and pathological processes of the central nervous system（CNS）.Kalirin7（Ka17）,a major isoform of Kalirin,is primary expression in the adult nervous system,and has a pivotal role in maintaining dendritic spines and synapse function.Previous study on Kal7 showed that the phosphorylation of Ka17 on Thr¹⁵⁹⁰ could increase its GEF activity slightly,changing its solubility properties and the morphology in PC 12 cells.However,whether the phosphorylation of Thr¹⁵⁹⁰ on Kal7 influences Kal7 mediated spine mophology and further effects on synaptic genesis and function is still unknown.BDNF,a pivotal neurotrophin,mediates dendritic spine growth and synaptic plasticity,but there is no study about Kal7 involving in BDNF regulating process.A number of studies revealed that cocaine exposure increased DA（Dopamine）neurons spine density within VTA,whereas we don’t know if Kal7 has a relationship with cocaine induced dendritic spine increase of dopaminergic neuron in VTA.Hence,to study the mechanism of Kal7 regulating neuroplasticity in different physiological processes is a vital strategy for treating neuroplasticity related diseases.The results showed that:1.Both Kal7 T/A and T/D mutants increased spine density as well as wild-type（Wt）Kal7,but the spine size were much different.Activiation of Thr¹⁵⁹⁰ induced a significant enlargement of spine size,while blocking the phosphorylaton of Thr¹⁵⁹⁰,the spine size shrank a lot compared with the WT Kal7.2.The levels of NR2B and GluRlin Ka17 T/D positive synapses were increased xwhile both were not altered by expression of Kal7 T/A in comparison to Wt Kal7.3.BDNF increased spine density and Vglutl-PSD95 co-expression along dendrite in cortical culture neurons,Kal7-shRNA infected neuron blocked this response but Scamble-shRNA didn’t.4.Kal7 was co-expressed with TH in VTA,and cocaine exposure increased co-expression of Ka17 and TH within VTA.5.The locomotion activity of rats increased in response to cocaine exposure,Golgi staining results showed spine density increased on DA neurons within VTA,and WB data indicated the expression of Ka17 and PSD95 were increased in VTA.6.Cocaine treatment both enhanced the locomotion activity of Wt and Ka17KO mice,but on 6th cocoaine injection,Wt mice locomotion was remarkable higher than Ka17KO mice,and spine density on DA neurons increased in Wt group compared with Kal7KO mice.So we concluded that:1.In rat culcured neurons,activation of Thr¹⁵⁹⁰ induced a significant increase of spine density and spines maturation,it mean the phosphalation site of Thr¹⁵⁹⁰ played an important role in the regulation of Kal7 on spine growth.2.The phosphorylation of Kal7 Thr¹⁵⁹⁰ affected spine morphology and synaptic function,via its effects on both NR2B-containing NMDA receptors and AMPA receptor localization during synaptogenesis.3.Exogenous BDNF stimulated spine density and synapse number increased in cortical culture neuron,Kal7-shRNA knockdown endogenous kal7 blocked the effects of BDNF.It revealed Kal7 was required for BDNF stimulated spine growth and synaptogenesis.4.Cocaine addiction enhanced animal locomotion activity,increased spine density,and rasied the content of PSD95 and Kal7 in VTA.Ka17KO-Coc mice showed a lower locomotion activity compared to Wt-Coc group,and no change on spine density comparison to Kal7KO-Sal was found.It indicated that Kal7 was involved in cocaine induce locomotion activity and was required for cocaine stimulated spine density increase on DA in VTA.All togetiher,our research showed that Ka17 and its Thr¹⁵⁹⁰ phospholation played an indispensable role in induced spine growth,BDNF stimulated spine growth and synaptogenesis,and cocaine induced spine growth on DA in VTA.More works need doing about the role of Kal7 in more neurological diseases.