MicroRNA-132 regulates recognition memory and synaptic plasticity in the perirhinal cortex

Identification of particular groups of microRNAs that positively or negatively impact on beta cell function in obese models of type 2 diabetes

AIMS/HYPOTHESIS

MicroRNAs are key regulators of gene expression involved in health and disease. The goal of our study was to investigate the global changes in beta cell microRNA expression occurring in two models of obesity-associated type 2 diabetes and to assess their potential contribution to the development of the disease.

METHODS

MicroRNA profiling of pancreatic islets isolated from prediabetic and diabetic db/db mice and from mice fed a high-fat diet was performed by microarray. The functional impact of the changes in microRNA expression was assessed by reproducing them in vitro in primary rat and human beta cells.

RESULTS

MicroRNAs differentially expressed in both models of obesity-associated type 2 diabetes fall into two distinct categories. A group including miR-132, miR-184 and miR-338-3p displays expression changes occurring long before the onset of diabetes. Functional studies indicate that these expression changes have positive effects on beta cell activities and mass. In contrast, modifications in the levels of miR-34a, miR-146a, miR-199a-3p, miR-203, miR-210 and miR-383 primarily occur in diabetic mice and result in increased beta cell apoptosis. These results indicate that obesity and insulin resistance trigger adaptations in the levels of particular microRNAs to allow sustained beta cell function, and that additional microRNA deregulation negatively impacting on insulin-secreting cells may cause beta cell demise and diabetes manifestation.

CONCLUSIONS/INTERPRETATION

We propose that maintenance of blood glucose homeostasis or progression toward glucose intolerance and type 2 diabetes may be determined by the balance between expression changes of particular microRNAs.

Loss of microRNA-132 predicts poor prognosis in patients with primary osteosarcoma

MicroRNA-132 (miR-132), an angiogenic growth factor inducible microRNA in the endothelium, facilitates pathological angiogenesis. Previous study showed that miR-132 was downregulated in human osteosarcoma. However, its functional attributes associated with tumor progression of osteosarcoma have not been fully elucidated. The aim of this study was to investigate the clinical significance of miR-132 expression in human osteosarcoma. miR-132 expression was detected by quantitative reverse transcription polymerase chain reaction using 166 pairs of osteosarcoma and noncancerous bone tissues. Then, the association of miR-132 expression with clinicopathological factors or survival of osteosarcoma patients was also evaluated. miR-132 expression was significantly lower in osteosarcoma tissues than that in corresponding noncancerous bone tissues (P < 0.001). In addition, miR-132 expression was decreased in the osteosarcoma specimens with advanced clinical stage (P = 0.009), positive distant metastasis (P = 0.006), and poor response to chemotherapy (P = 0.009). Moreover, both the univariate and multivariate analyses showed that osteosarcoma patients with low miR-132 expression had poorer overall and disease-free survival (both P < 0.001), and low miR-132 expression was an independent prognostic factor for both overall (P = 0.001) and disease-free survival (P = 0.006). These findings offer the convinced evidence for the first time that miR-132 may participate in tumor progression of osteosarcoma and loss of miR-132 expression may be a predictor for unfavorable outcome of osteosarcoma patients.

MicroRNA-132 may play a role in coexistence of depression and cardiovascular disease: a hypothesis

Different individuals have different degrees of neuroplasticity due to their different experiences. Neuroplasticity may play a role in individual differences among neuropsychiatric disease treatment efficacy. Since the nervous system monitors and coordinates internal organ function, neuroplasticity may be associated with other diseases. Cardiovascular disease (CVD) is associated with depression, which is a disorder of disrupted neuroplasticity. MicroRNA-132 (miR-132) has a roles in neuroplasticity and cardiovascular function. Thus, we hypothesize that miR-132 may play a role in coexistence of depression and CVD.

In vivo knockdown of hippocampal miR-132 expression impairs memory acquisition of trace fear conditioning

MicroRNA-132 (miR-132) has been demonstrated to affect multiple neuronal functions, including dendritic growth and spinogenesis in cultured neurons and brain slices, as well as learning behavior of animals. However, its role in acquisition of temporal-associated memory remains unclear. In this study, we demonstrated that the mature miR-132 level in mouse hippocampus was significantly increased at 30 min after trace fear conditioning, a type of temporal-associated learning, and returned to baseline values in 2 h. We then knocked down miR-132 expression in vivo by infusing a lentivector expressing anti-miR-132 hairpin RNA into the third ventricle near the anterior hippocampi such RNA diffused laterally to both hippocampal formations, later confirmed by histological analysis. This approach successfully reduced hippocampal miR-132 expression in both naïve and trace fear conditioned groups, and impaired acquisition of trace fear memory in mice. To our knowledge, this result is the first demonstration of change in temporal learning behavior by reducing microRNA (miRNA) level specifically in the hippocampal region.

De-repression of FOXO3a death axis by microRNA-132 and -212 causes neuronal apoptosis in Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial and fatal neurodegenerative disorder for which the mechanisms leading to profound neuronal loss are incompletely recognized. MicroRNAs (miRNAs) are recently discovered small regulatory RNA molecules that repress gene expression and are increasingly acknowledged as prime regulators involved in human brain pathologies. Here we identified two homologous miRNAs, miR-132 and miR-212, downregulated in temporal cortical areas and CA1 hippocampal neurons of human AD brains. Sequence-specific inhibition of miR-132 and miR-212 induces apoptosis in cultured primary neurons, whereas their overexpression is neuroprotective against oxidative stress. Using primary neurons and PC12 cells, we demonstrate that miR-132/212 controls cell survival by direct regulation of PTEN, FOXO3a and P300, which are all key elements of AKT signaling pathway. Silencing of these three target genes by RNAi abrogates apoptosis caused by the miR-132/212 inhibition. We further demonstrate that mRNA and protein levels of PTEN, FOXO3a, P300 and most of the direct pro-apoptotic transcriptional targets of FOXO3a are significantly elevated in human AD brains. These results indicate that the miR-132/miR-212/PTEN/FOXO3a signaling pathway contributes to AD neurodegeneration.