Inhibition of phagocytosis reduced the classical activation of BV2 microglia induced by amyloidogenic fragments of beta-amyloid and prion proteins

The Role of Glial Cells in Neurobiology and Prion Neuropathology

Prion diseases are rare and neurodegenerative diseases that are characterized by the misfolding and infectious spread of the prion protein in the brain, causing progressive and irreversible neuronal loss and associated clinical and behavioral manifestations in humans and animals, ultimately leading to death. The brain has a complex network of neurons and glial cells whose crosstalk is critical for function and homeostasis. Although it is established that prion infection of neurons is necessary for clinical disease to occur, debate remains in the field as to the role played by glial cells, namely astrocytes and microglia, and whether these cells are beneficial to the host or further accelerate disease. Here, we review the current literature assessing the complex morphologies of astrocytes and microglia, and the crosstalk between these two cell types, in the prion-infected brain.

The Role of Inflammasomes in the Pathogenesis of Neurodegenerative Diseases

Abstract—Protein misfolding and accumulation of protein aggregates is a distinctive feature of most neurodegenerative diseases. They lead to disruption of cellular homeostasis, loss of synaptic connections, and therefore cellular apoptosis. It has been demonstrated that some innate immune responses play an important role in the emergence and progression of neurodegenerative diseases. Inflammasomes are components of innate immunity that play a major role in the maintenance of chronic inflammation. Inflammasomes function as intracellular sensors, detecting both exogenous and endogenous stimuli. They also take part in caspase-1 activation and the synthesis of pro-inflammatory cytokines. In the central nervous system (CNS), inflammasomes are predominantly expressed by microglia, the key cells of innate immunity responsible for activation and maintenance of inflammation. In addition to microglia, inflammasomes can be expressed and activated by astrocytes and neurons, as well as infiltrating myeloid cells. Understanding the mechanisms of activation and functioning of inflammasomes is crucial for the development of novel drugs targeted at modulation of the immune response associated with their excessive activation. This review provides up-to-date information on the inflammasome structure and mechanisms of action, the role of protein misfolding, aggregation and the influence of these factors on inflammasome activation, as well as potential therapeutic targets in neurodegenerative diseases.

Vitamin D2 suppresses amyloid-β 25-35 induced microglial activation in BV2 cells by blocking the NF-κB inflammatory signaling pathway

AIMS

Present emerging world is emphasizing the implication of vitamin D deficiency associated with development of inflammation and neurodegenerative disorder like Alzheimer's disease (AD). The chief neuropathological hallmark of AD is aggregation of amyloid-beta (Aβ) peptides surrounding microglial cells in human brain. Microglial activation plays a key role in inflammatory response and neuronal injury. Naturally abundant vitamin D2 (VD2) exhibiting anti-inflammatory activities are yet to explore more. This study has investigated the inhibitory effect of VD2 on inflammatory activities of BV2 microglial cells.

MAIN METHODS

Cellular compatibility of VD2 and Aβ25-35 protein in treated BV2 microglial cells were measured by CCK-8 assay. Induction of iNOS, COX-2 and NF-κB signaling cascade were measured by western blotting, whereas pro-inflammatory cytokines were measured by ELISA. In addition, generation of ROS was detected by fluorescence intensity.

KEY FINDINGS

Morphological observations showed that Aβ25-35 induced BV2 cells stimulation noticeably got reduced in VD2 pre-treated group at 24h time period. Anti-inflammatory activities of VD2 was observed demonstrating the inhibition of up-regulated iNOS and COX-2 protein expression further confirmed by attenuating the activated microglia released pro-inflammatory cytokines IL-1β, IL-6, TNF- α and ROS, while blocking the phosphorylation of NF-κB p65 in nucleus by preventing IκB-α degradation and phosphorylation in cytosol.

SIGNIFICANCE

The present study revealed that VD2 blocked the phosphorylation of NF-κB inflammatory signaling pathway in Aβ25-35 induced activated BV2 microglial cells by suppressing ROS generation and inflammatory cytokines. Our finding suggests that vitamin D2 has therapeutic potential against inflammation and Alzheimer's disease.

The Protein Tyrosine Kinase Inhibitor Tyrphostin 23 Strongly Accelerates Glycolytic Lactate Production in Cultured Primary Astrocytes

Tyrphostin 23 (T23) is a well-known inhibitor of protein tyrosine kinases. To investigate potential acute effects of T23 on the viability and the glucose metabolism of brain cells, we exposed cultured primary rat astrocytes to T23 for up to 4 h. While the viability and the morphology of the cultured astrocytes were not acutely affected by the presence of T23 in concentrations of up to 300 µM, this compound caused a rapid, time- and concentration-dependent increase in glucose consumption and lactate release. Maximal effects on glycolytic flux were found for incubations with 100 µM T23 for 2 h which doubled both glucose consumption and lactate production. The stimulation of glycolytic flux by T23 was reversible, completely abolished upon removal of the compound and not found in presence of other known inhibitors of endocytosis. Structurally related compounds such as tyrphostin 25 and catechol or modulators of AMP kinase activity did neither affect the basal nor the T23-stimulated lactate production by astrocytes. In contrast, the presence of the phosphatase inhibitor vanadate completely abolished the stimulation by T23 of astrocytic lactate production in a concentration-dependent manner. These data suggest that T23-sensitive phosphorylation/dephosphorylation events are involved in the regulation of astrocytic glycolysis.

Toll-like receptor 2 deficiency shifts PrP106-126-induced microglial activation from a neurotoxic to a neuroprotective phenotype

Prion diseases are fatal neurodegenerative diseases characterized by spongiform change, neuronal loss, and gliosis involving microglial activation in the central nervous system. Microglial activation is thought to play a key role in the pathogenesis of prion disease; however, the molecular mechanisms underlying prion-induced microglial activation are not well understood. The present study underlines the importance of toll-like receptor (TLR)-2 in mediating PrP106-126-induced microglial activation. We found that PrP106-126 induced expression of proinflammatory molecules and TLR2 in microglial cells; however, functional blocking antibodies against TLR2 suppressed PrP106-126-induced expression of proinflammatory molecules. PrP106-126-induced expression of proinflammatory molecules was also reduced in microglial cells isolated from TLR2-/- mice compared to those isolated from wild-type mice. Consistent with the importance of nuclear factor kappa B (NF-κB) mediating TLR functions, NF-κB inhibition also inhibited PrP106-126-induced expression of proinflammatory molecules. To better understand the effect of TLR2 deficiency on active microglial cells, we studied the expression of Arg1 and Mrc1 and anti-inflammatory cytokines, which indicated that TLR2 deficiency in microglial cells results in a shift from neurotoxic to neuroprotective phenotype. Taken together, our results indicate that the TLR2 signaling pathway mediates PrP106-126-induced microglial activation and potentially reveal new therapeutic strategies for prion diseases that modulate TLR2 signaling.