Nicotine abolishes memory‐related synaptic strengthening and promotes synaptic depression in the neurogenic dentate gyrus of miR‐132/212 knockout mice

Abstract

Micro‐RNAs (miRNAs) are highly evolutionarily conserved short‐length/noncoding RNA molecules that modulate a wide range of cellular functions in many cell types by regulating the expression of a variety of targeted genes. miRNAs have also recently emerged as key regulators of neuronal genes mediating the effects of psychostimulant drugs and memory‐related neuroplasticity processes. Smoking is a predominant addictive behaviour associated with millions of deaths worldwide, and nicotine is a potent natural psychoactive agonist of cholinergic receptors, highly abundant in cigarettes. The influence of miRNAs modulation on cholinergic signalling in the nervous system remains however poorly explored. Using miRNA knockout mice and biochemical, electrophysiological and pharmacological approaches, we examined the effects of miR‐132/212 gene disruption on the levels of hippocampal nicotinic acetylcholine receptors, total ERK and phosphorylated ERK (pERK) and MeCP2 protein levels, and studied the impact of nicotine stimulation on hippocampal synaptic transmission and synaptic depression and strengthening. miR‐132/212 deletion significantly altered α7‐nAChR and pERK protein levels, but not total ERK or MeCP2, and resulted in both exacerbated synaptic depression and virtually abolished memory‐related synaptic strengthening upon nicotine stimulation. These observations reveal a functional miRNAs/nicotinergic signalling interplay critical for nicotinic‐receptor expression and neuroplasticity in brain structures relevant for drug addiction and learning and memory functions.

miRNA-132/212 Gene-Deletion Aggravates the Effect of Oxygen-Glucose Deprivation on Synaptic Functions in the Female Mouse Hippocampus

“…Acutely dissected hippocampal slices obtained from miRNA 132/212 −/− mice and WT littermates ( n = 6–7 animals per experimental group) were prepared as previously described [ 22 , 51 , 52 , 53 ], with slight modifications. Briefly, mice were sacrificed by swift cervical dislocation and subsequent sharp-blade decapitation.…”

“…We extracted brains and isolated whole hippocampi from female miRNA 132/212 −/− and WT control mice ( n = 5 animals per group) as previously described, with minor modifications [ 22 , 51 , 52 , 53 ]. Brains were quickly extracted, following swift cervical dislocation and sharp blade decapitation, and immersed in ice-cold artificial cerebrospinal fluid (aCSF) with pH balanced to 7.35–7.40.…”

“…Micro-RNAs, a class of single stranded (∼21–22 nucleotide long) non-coding RNAs, are highly evolutionarily conserved, potent and selective post-transcriptional regulators of mRNA translation [ 10 , 11 , 12 , 13 ]. In the central nervous system (CNS), miRNAs have been implicated in diverse physiological processes such as neuronal development [ 14 , 15 , 16 , 17 ], adult neurogenesis [ 18 ], and synaptic transmission and plasticity [ 19 , 20 , 21 , 22 , 23 ]. Correspondingly, dysregulation of miRNAs has been associated with hallmarks of pathogenesis for a variety of debilitating neurological disorders including epilepsy [ 24 , 25 , 26 , 27 ], Alzheimer’s disease [ 28 , 29 , 30 , 31 ], and ischemic brain injuries [ 5 , 6 , 7 , 8 , 9 ].…”

“…Interestingly, the neuron-enriched miRNA 132/212 cluster has been implicated both in the physiological regulation of the molecular mechanisms underlying higher order cognitive functions such as learning and memory ex and in vivo [ 16 , 21 , 22 , 33 ], and in resilience to hypoxic and ischemic insults of various cell lines in vitro [ 34 , 35 , 36 ]. However, miRNA 132/212 regulation in cerebral ischemia–reperfusion injuries and its putative role in the pathophysiology of ischemic injury still remains controversial [ 35 , 36 , 37 ].…”

“…A putative role of the miRNA 132/212 cluster in the regulation of synaptic transmission during the acute phase of OGD has yet to be elucidated. Although independently implicated as a key regulator of synaptic transmission [ 21 , 22 ] and the adaptive response to ischemia [ 35 , 36 ], the putative role of the miRNA 132/212 cluster in the acute response of synaptic transmission to ischemia–reperfusion insults remains scarcely researched. Thus, we adapted a widely established ex vivo model of OGD (see [ 46 ] for a methodological review) to study the role of miRNAs 132/212 in the response of synaptic transmission to repeated ischemia–reperfusion insults in the dentate gyrus, a brain structure critical for learning and memory, and adult neurogenesis [ 47 , 48 ].…”