Suv39h1 Silencing Recovers Memory Decline in Scopolamine-Induced Amnesic Mouse Model.

Histone post-translational modifications play an important role in the regulation of long-term memory and modulation of expression of neuronal immediate early genes (IEGs). The lysine methyltransferase KMT1A/ Suv39h1 (a mammalian ortholog of the Drosophila melanogaster SU (VAR) 3-9) aids in the methylation of histone H3 at lysine 9. We previously reported that age-related memory decline is associated with an increase in Suv39h1 expression in the hippocampus of male mice. The scopolamine-induced amnesic mouse model is a well-known animal model of memory impairment. In the current study, we have made an attempt to find a link between the changes in the H3K9 trimethylation pattern and memory decline during scopolamine-induced amnesia. It was followed by checking the effect of siRNA-mediated silencing of hippocampal Suv39h1 on memory and expression of neuronal IEGs. Scopolamine treatment significantly increased global levels of H3K9me3 and Suv39h1 in the amnesic hippocampus. Suv39h1 silencing in amnesic mice reduced H3K9me3 levels at the neuronal IEGs (Arc and BDNF) promoter, increased the expression of Arc and BDNF in the hippocampus, and improved recognition memory. Thus, these findings suggest that the silencing of Suv39h1 alone or in combination with other epigenetic drugs might be effective for treating memory decline during amnesia.

Muscarinic Acetylcholine Receptors-Mediated Activation of PKC Restores the Hippocampal Immediate Early Gene Expression and CREB Phosphorylation in Scopolamine-Induced Amnesic Mice.

Amnesia is the inability to store new information and recall old memories. After the postulation of cholinergic hypothesis of geriatric memory dysfunction, the cholinergic signaling became a popular target to understand the underlying molecular mechanism of amnesia and its recovery. Scopolamine is a non-selective cholinergic receptor antagonist and induces amnesia through downregulation of synaptic plasticity genes including immediate early genes (IEGs). Scopolamine-induced amnesic mouse model is widely used to study the memory impairment that mimics the pathophysiology of aging, neurodegenerative, and neuropsychiatric disorders. However, a detailed understanding of cholinergic signaling-mediated regulation of plasticity-related gene expression remains elusive. Therefore, we have investigated the role of muscarinic acetylcholine receptors (mAChRs) and their downstream mediator protein kinase C (PKC) in the regulation of IEGs expression in amnesic mice hippocampus. Pilocarpine, a mAChRs agonist, was used to activate the cholinergic signaling in scopolamine-induced amnesia. Further, a PKC activator bryostatin 1 was used to understand the sole involvement of PKC as a downstream mediator of mAChRs-mediated signaling. Pilocarpine treatment significantly restored the scopolamine-induced impaired recognition memory and downregulated hippocampal IEGs expression and phosphorylation of ERK1/2 (extracellular signal-regulated kinase 1/2) and CREB (cAMP response element-binding protein). On the other hand, the bryostatin 1-mediated activation of PKC in scopolamine-induced amnesia selectively restored the hippocampal IEGs expression, recognition memory, and phosphorylation of ERK1/2 and CREB. Taken together, our findings suggest that mAChRs and their downstream mediator PKC regulate the hippocampal IEGs expression and ERK1/2-mediated CREB phosphorylation in scopolamine-induced amnesic mice.

Vitamin B12-folic acid supplementation regulates neuronal immediate early gene expression and improves hippocampal dendritic arborization and memory in old male mice.

As the relationship among diet, brain aging and memory is complex, it provides ample opportunity for research in multiple directions including behaviour, epigenetics and neuroplasticity. Nutritional deficiencies together with genetic and environmental factors are the major cause of many age-associated pathologies including memory loss. A compromised vitamin B12-folate status in older people is highly prevalent worldwide. Researchers have established a close association between the adequate level of B12-folate and the maintenance of cognitive brain functions. One of the main reasons for age-associated memory loss is downregulation of neuronal immediate early genes (nIEGs). Therefore, we hypothesize here that vitamin B12-folic acid supplementation in old mice can improve memory by altering the expression status of nIEGs. To check this, 72-week-old male Swiss albino mice were orally administered with 2 µg of vitamin B12 and 22 µg of folic acid/mouse/day for eight weeks. Such supplementation improved recognition memory in old and altered the expression of nIEGs. The expression of nIEGs was further found to be regulated by changes in DNA methylation at their promoter regions and CREB phosphorylation (pCREB). In addition, Golgi-Cox staining showed significant improvement in dendritic length, number of branching points and spine density of hippocampal CA1 pyramidal neurons by B12-folic acid supplementation. Taken together, these findings suggest that vitamin B12-folic acid supplementation regulates nIEGs expression and improves dendritic arborization of hippocampal neurons and memory in old male mice.

Increase in hippocampal histone H3K9me3 is negatively correlated with memory in old male mice.

With advancing age, memory declines through different mechanisms including dysregulation of expression of synaptic plasticity genes in hippocampus. Increasing evidences suggest that these synaptic plasticity genes are regulated through epigenetic modifications. Recently we have reported that the neuronal immediate early genes (IEGs) are regulated by DNA methylation and histone acetylation, and their expression is downregulated in the hippocampus of old male mice, which subsequently results in decline of memory. These modifications do not work in isolation but act synergistically and lead to distinct regulation of gene expression. Therefore, in the present study, we have explored whether these genes are also regulated by histone methylation and this has any correlation with memory decline during aging. This study for the first time reports involvement of H3K9me3 in the regulation of neuronal IEGs during aging. Using novel object recognition and Y-maze test, the recognition and spatial memory was checked in male mice of different ages and it was found to decline in old. We have examined the expression of H3K9me3 specific histone methyltransferases and noted that only SUV39H1 (suppressor of variegation 3-9 homolog 1) increased significantly in old. Also the global H3K9me3 level was high in the hippocampus of old male mice. Further, chromatin immunoprecipitation assay revealed rise in H3K9me3 level at the promoter of IEGs in old as compared to young male mice. The immunofluorescence analysis also showed varying pattern of H3K9me3 expression in different subregions of hippocampus with aging. These findings showed negative correlation of increase in hippocampal histone H3K9me3 with memory decline in old male mice. Diagram here represents that during aging, there is increase in expression of SUV39H1. Such increased enzyme upregulates global and gene specific methylation in hippocampus of old male mice. H3K9me3 level increases at the promoter of neuronal IEGs leading to heterochromatisation and hence decrease in their expression and ultimately decline in memory during aging.