Structural analysis of the microglia-interneuron interactions in the CA1 hippocampal area of the APP/PS1 mouse model of Alzheimer's disease.

Microglia can interact with glutamatergic neurons and, through control of synaptic elements, regulate their physiological function. Much less is known about the partnership between microglia and GABAergic inhibitory interneurons. Here, we compared the interactions between microglia and parvalbumin (PV+) and somatostatin (SOM+) expressing interneurons in the CA1 hippocampal area of APP/PS1 transgenic mice that mimic certain aspects of the Alzheimer's disease (AD). We first uncovered a high level of interactions between microglia and two types of interneurons, with 98% of SOM+ and 90% of PV+ cells receiving different types of putative microglial contacts. The latter included the microglia soma to the interneuron soma (SomaMG -to-SomaIN ), the microglia process to the interneuron soma (ProcessMG -to-SomaIN ) and the microglia process to the interneuron dendrite (ProcessMG -to-DendIN ) interactions. Moreover, we found significantly larger areas of interaction for the SomaMG -to-SomaIN and the ProcessMG -to-DendIN type of contacts between microglia and SOM+ cells. In contrast, PV+ cells exhibited larger areas for the ProcessMG -to-SomaIN interactions. Second, in APP/PS1 mice, although the overall microglia interactions with interneurons remained preserved, the fraction of interneurons receiving putative microglia contacts on their dendrites was reduced, and larger areas of interactions were observed for somatic contacts, suggesting a stronger modulation of the interneuron output by microglia in AD. In summary, these results reveal microglia as important partners of hippocampal PV+ and SOM+ GABAergic cells, with interneuron type-specific pattern of interactions. Thus, microglia may play an essential role in the operation of interneurons under normal conditions and their dysfunction in disease.

Roles and Interaction of the MAPK Signaling Cascade in Aß25-35-Induced Neurotoxicity Using an Isolated Primary Hippocampal Cell Culture System.

Alzheimer's disease (AD) is characterized with increased formation of amyloid-ß (Aß) in the brain. Aß peptide toxicity is associated with disturbances of several intracellular signaling pathways such as mitogen activated protein kinases (MAPKs). The aim of this study was to investigate the role of MAPKs and their interactions in Aß-induced neurotoxicity using isolated hippocampal neurons from the rat. Primary hippocampal cells were cultured in neurobasal medium for 4 days. Cells were treated with Aß25-35 and/or MAPKs inhibitors for 24 h. Cell viability was determined by an MTT assay and phosphorylated levels of P38, JNK, and ERK were measured by Western blots. Aß treatment (10-40 µM) significantly decreased hippocampal cell viability in a dose-dependent manner. Inhibition of P38 and ERK did not restore cell viability, while JNK inhibition potentiated the Aß-induced neurotoxicity. Compared to the controls, Aß treatment increased levels of phosphorylated JNK, ERK, and c-Jun, while it had no effect on levels of phosphorylated P38. In addition, P38 inhibition led to decreased expression levels of phosphorylated ERK; inhibition of JNK resulted in decreased expression of c-Jun; and inhibition of ERK, decreased phosphorylated levels of JNK. These results strongly suggest that P38, ERK, and JNK are not independently involved in Aß-induced toxicity in the hippocampal cells. In AD, which is a multifactorial disease, inhibiting a single member of the MAPK signaling pathway, does not seem to be sufficient to mitigate Aß-induced toxicity and thus their interactions with each other or potentially with different signaling pathways should be taken into account.

The neuroprotective effect of agmatine against amyloid ß-induced apoptosis in primary cultured hippocampal cells involving ERK, Akt/GSK-3ß, and TNF-α.

ß-Amyloid peptide (Aß), the major element of senile plaques in Alzheimer's disease (AD), has been found to accumulate in brain regions critical for memory and cognition. Deposits of Aß trigger neurotoxic events which lead to neural apoptotic death. The present study examined whether agmatine, an endogenous polyamine formed by the decarboxylation of L-arginine, possesses a neuroprotective effect against Aß-induced toxicity. Primary rat hippocampal cells extracted from the brains of 18-19-day-old embryos were exposed to 10 µM of Aß (25-35) in the absence or presence of agmatine at 150 or 250 µM. Additionally, the involvement of Akt (Protein Kinae B), GSK-3ß (glycogen synthase kinase 3-ß), ERK (Extracellular Signal-Regulated Kinase) and TNF-α (Tumor necrosis factor-α) in the agmatine protection against Aß-induced neurotoxicity was investigated. Agmatine significantly prevented the effect of Aß exposure on cell viability and caspase-3 assays. Furthermore, agmatine considerably restored Aß-induced decline of phospho-Akt and phospho-GSK and blocked Aß-induced increase of phospho-ERK and TNF-alpha. Taken together, these findings might shed light on the protective effect of agmatine as a potential therapeutic agent for AD.

Investigating the role of P38, JNK and ERK in LPS induced hippocampal insulin resistance and spatial memory impairment: effects of insulin treatment.

Despite the consensus that neuro-inflammation and insulin resistance (IR) are two hallmarks of Alzheimer disease (AD), the molecular mechanisms responsible for the development of IR remain uncharacterized. MAPKs are signaling molecules that are implicated in the pathology of AD and have a role in IR development. Given that inflammatory mediators are shown to interfere with insulin signaling pathway in different cell types, the present work aimed to investigate whether neuro-inflammation induced memory loss is associated with hippocampal IR and whether insulin treatment protects against this IR. Subsequently, possible roles of MAPKs in this situation were investigated. Male Wistar rats were cannulated, and LPS (15 µg, day 0), insulin (3 mU) or saline (vehicle) were administered intra-cerebroventricularly (ICV) (days 1-6). Spatial memory performance was assessed during days 7-10 by Morris Water Maze test. Consequently, analysis of the amount of hippocampal phosphorylated forms of P38, JNK, ERK, IRS1 (ser307) and Akt (ser473) were done by Western blot. The outcomes indicated that while LPS induced memory loss and hippocampal IR (shown by elevated IRS1 and decreased Akt phosphorylation), insulin treatment nullified these effects. Molecular results also showed that LPS mediated IR and memory loss are associated with P38 but not JNK and ERK activation; this P38 activation was reversed by insulin treatment. These observations implied that one of the ways by which neuro-inflammation participates in AD is via induction of IR. It seems that this IR is mainly mediated by P38. Therefore, P38 could be considered as a molecular target for preventing IR development.