Neuronal Menin Overexpression Rescues Learning and Memory Phenotype in CA1-Specific α7 nAChRs KD Mice

Clinically Defined Mutations in MEN1 Alter Its Tumor-suppressive Function Through Increased Menin Turnover

Loss of the tumor suppressor protein menin is a critical event underlying the formation of neuroendocrine tumors (NET) in hormone-expressing tissues including gastrinomas. While aberrant expression of menin impairs its tumor suppression, few studies explore the structure-function relationship of clinical multiple endocrine neoplasia, type 1 (MEN1) mutations in the absence of a complete LOH at both loci. Here, we determined whether clinical MEN1 mutations render nuclear menin unstable and lead to its functional inactivation. We studied the structural and functional implications of two clinical MEN1 mutations (R516fs, E235K) and a third variant (A541T) recently identified in 10 patients with gastroenteropancreatic (GEP)-NETs. We evaluated the subcellular localization and half-lives of the mutants and variant in Men1-null mouse embryo fibroblast cells and in hormone-expressing human gastric adenocarcinoma and NET cell lines. Loss of menin function was assessed by cell proliferation and gastrin gene expression assays. Finally, we evaluated the effect of the small-molecule compound MI-503 on stabilizing nuclear menin expression and function in vitro and in a previously reported mouse model of gastric NET development. Both the R516fs and E235K mutants exhibited severe defects in total and subcellular expression of menin, and this was consistent with reduced half-lives of these mutants. Mutated menin proteins exhibited loss of function in suppressing tumor cell proliferation and gastrin expression. Treatment with MI-503 rescued nuclear menin expression and attenuated hypergastrinemia and gastric hyperplasia in NET-bearing mice. Clinically defined MEN1 mutations and a germline variant confer pathogenicity by destabilizing nuclear menin expression.

Significance

We examined the function of somatic and germline mutations and a variant of MEN1 sequenced from gastroenteropancreatic NETs. We report that these mutations and variant promote tumor cell growth and gastrin expression by rendering menin protein unstable and prone to increased degradation. We demonstrate that the menin-MLL (mixed lineage leukemia) inhibitor MI-503 restores menin protein expression and function in vitro and in vivo, suggesting a potential novel therapeutic approach to target MEN1 GEP-NETs.

Choline alleviated perinatal fluoride exposure-induced learning and memory impairment through α4β2 nAChRs and α7 nAChRs in offspring mice

Fluoride pollution is widely present in the living environment. As a critical period of brain development, the perinatal period is extremely vulnerable to fluoride. Studies have found that choline can protect the brain's memory and enhance the ability to focus. However, the effect of choline on perinatal fluoride-induced nerve damage remains unclear. Therefore, 32 Kunming newly conceived female mice and their offspring mice were randomly divided into control, NaF, LC + NaF, and HC + NaF groups, and the HE staining, Y-maze test, RT-PCR, western blotting, immunohistochemistry, etc. were used in this study. The results showed that fluoride decreased the brain organ coefficients and brain protein content (p < 0.05, p < 0.01), and caused histomorphological damage in the hippocampus and cortex, which suggested that fluoride affected the development of the brain and damaged the brain. Moreover, the results of the Y-maze test showed that fluoride increased the number of learning days, error reaction time, and total reaction time, and decreased the AchE activity in the brain (p < 0.05, p < 0.01), which indicated that fluoride reduced the learning and memory ability of the mice. Besides, the results showed that fluoride decreased the mRNA and protein expression levels of α4β2 nAChRs and α7 nAChRs in the hippocampus and cortex (p < 0.05, p < 0.01). However, perinatal choline supplementation reversed the aforementioned fluoride-induced changes. In short, these results demonstrated that choline alleviated perinatal fluoride-induced learning and memory impairment, which will provide a rationale for the mitigation and prevention of fluoride-induced brain damage.

Astrocytes amplify neurovascular coupling to sustained activation of neocortex in awake mice

Functional hyperemia occurs when enhanced neuronal activity signals to increase local cerebral blood flow (CBF) to satisfy regional energy demand. Ca2+ elevation in astrocytes can drive arteriole dilation to increase CBF, yet affirmative evidence for the necessity of astrocytes in functional hyperemia in vivo is lacking. In awake mice, we discovered that functional hyperemia is bimodal with a distinct early and late component whereby arteriole dilation progresses as sensory stimulation is sustained. Clamping astrocyte Ca2+ signaling in vivo by expressing a plasma membrane Ca2+ ATPase (CalEx) reduces sustained but not brief sensory-evoked arteriole dilation. Elevating astrocyte free Ca2+ using chemogenetics selectively augments sustained hyperemia. Antagonizing NMDA-receptors or epoxyeicosatrienoic acid production reduces only the late component of functional hyperemia, leaving brief increases in CBF to sensory stimulation intact. We propose that a fundamental role of astrocyte Ca2+ is to amplify functional hyperemia when neuronal activation is prolonged.

Selective Menin Deletion in the Hippocampal CA1 Region Leads to Disruption of Contextual Memory in the MEN1 Conditional Knockout Mouse: Behavioral Restoration and Gain of Function following the Reintroduction of MEN1 Gene

Cholinergic neuronal networks in the hippocampus play a key role in the regulation of learning and memory in mammals. Perturbations of these networks, in turn, underlie neurodegenerative diseases. However, the mechanisms remain largely undefined. We have recently demonstrated that an in vitro MEN1 gene deletion perturbs nicotinic cholinergic plasticity at the hippocampal glutamatergic synapses. Furthermore, MEN1 neuronal conditional knockout in freely behaving animals has also been shown to result in learning and memory deficits, though the evidence remains equivocal. In this study, using an AVV viral vector transcription approach, we provide direct evidence that MEN1 gene deletion in the CA1 region of the hippocampus indeed leads to contextual fear conditioning deficits in conditional knockout animals. This loss of function was, however, recovered when the same animals were re-injected to overexpress MEN1. This study provides the first direct evidence for the sufficiency and necessity of MEN1 in fear conditioning, and further endorses the role of menin in the regulation of cholinergic synaptic machinery in the hippocampus. These data underscore the importance of further exploring and revisiting the cholinergic hypothesis that underlies neurodegenerative diseases that affect learning and memory.