Study On The Impact And Related Mechanism Of Dendritic Spine Morphology And Autophagy Induced By Pb Exposure

Lead (Pb) is one of important environmental pollutants, which mainly impaired learning and memory function. Our recent work showed Pb exposure reduced spine density in hippocampal neurons in rats, but the sensitivity of Pb-induced spine maturity with mixed factors (genderxagexbrain regions) remains unknown. What’s more, recent studies showed development Pb exposure might have an effect on the function of the nervous system at old age, however the molecular basis remains unclear.Objective This study aimed to systematically investigate the effect of Pb exposure on dendrite growth and spine maturity in rat brain with mixed factors (genderxagexbrain regions), as well as the potential mechanism. To explore the effect on autophagy caused by Pb exposure, further speculating the possible mechanism in neurodegenerative diseases response to Pb exposure.Methods 1. Female and male SD rats were feed with 250 ppm lead acetate solution until PND30, PND60, PND90, respectively. The Pb-exposed rat pups acquired Pb during lactation indirectly through the milk from their mothers and then directly after weaning at the postnatal day 21 (PND21). This in vivo experiment was conducted to study the impairment of Pb exposure on dendrite growth and spine maturity in rat brain with three factors (genderxagexbrain regions), further studying the potential mechanism. Golgi-Cox staining was used to examine dendrite length and spine maturity. Western blot assay was applied to measure NDR1/2 protein expression and real-time fluorescence quantitative PCR assay was used to examine mRNA levels.2. The experiment of the effect on autophagy response to Pb exposure was conducted in vitro. PC 12 cell line was exposed to 20μM lead acetate for 24h, and then MTT experiment was used to examine the cell viability, Western blot assay was applied to measure protein expression, real-time fluorescence quantitative PCR assay was used to examine mRNA levels and lysosomal staining experiment was used toexamine the lysosomal pH.Results 1. Pb exposure impaired development neuron dendritic length, and this impairment tended to female> male, hippocampus> medial. 2. Pb exposure induced sustained impairment of neuronal dendritic spine maturity from adolescence to adulthood. Besides, there were brain regions differences (the level of impairment: hippocampus> medial prefrontal cortex) and gender differences (the level of impairment:female> male) during adulthood(PND90).3.NDR1/2 kinase pathway was impaired by Pb exposure, the tendency of this impairment was similar to the result of neuronal dendritic spine maturity. So NDR1/2 kinase pathway might play a role in the process that Pb exposure inhibited neuronal dendritic spine maturity.4. Pb exposure blocked autophagy flux, Pb exposure inhibited the upstream of autophagy by regulating NDR1 protein and lysosome acidification further degradation of downstream of autophagy by presenilin 1.Conclusion This study aimed to explore the potential mechanism of the learning and memory functional impairment induced by Pb exposure from this two aspect:autophagy and the morphology of neuronal dendrite and dendritic spine.1. Pb exposure inhibited the neuronal dendrite growth and spine maturity, and this inhibition was subjected to gender differences, brain regions differences and age differences.2. Pb exposure impaired dendritic spine maturity through NDR1/2 kinase pathway.3. Pb exposure impaired the integrity of autophagy flux, autophagosome formation and autolysosome degradation was impaired by Pb exposure. However, the relationship between Pb exposure and neurodegenerative disease still remains elusive.