The role of cytosolic phospholipase A2 in microglial signaling pathways during neuroinflammation
Oxidative and nitrosative stress is known to play an important role in neurodegenerative and neuroinflammatory diseases, such as Alzheimer's disease, Parkinson's disease, ischemic[slash]hemorrhagic stroke, and traumatic brain injury. Microglia are the primary innate immune cells in the central nervous system (CNS). These cells are the first line of defense against foreign pathogens, and the exhibit multiple physiological roles including removing cellular debris and maintaining tissue homeostasis. Pathologic activation of microglia, which is frequently secondary to neurodegenerative or neuroinflammatory processes, can lead to the release of proinflammatory cytokines, reactive oxygen species (ROS), reactive nitrogenous species (RNS), excitotoxic neurotransmitters, metalloproteases, and other pro-inflammatory[slash]cytotoxic factors. Propagation of inflammation in neurodegenerative conditions and can be a contributor of neuronal cell death. Cytosolic phospholipase A2 (cPLA2) belongs to a family of phospholipases that act as the principle producers of arachidonic acid (AA) in cells. During the process of inflammation, AA released from phospholipids is metabolized by cyclooxygenase-1[slash]2 (COX1[slash]2) and lipoxygenases, and in turn can be converted to prostaglandins, prostacyclin and thromboxane. This is an important pathway of inflammation, with COX1[slash]2 being the popular target for non-steroidal anti-inflammatory drugs (NSAIDs). The role of cPLA2 and its downstream pathway has not been investigated in depth in microglial cells during CNS neuroinflammation. Using primary microglial culture prepared from cPLA2 knockout mice, we found that oxidative and nitrosative stress responses were significantly attenuated in cPLA2 knockout mice as compared with wildtype control. The same phenomenon was observed using pharmacological inhibition and siRNA knockdown of cPLA2 in BV2 microglial cells. Interestingly, unlike macrophages, inhibition of COX1[slash]2 did not result in significant decrease in oxidative[slash]nitrosative responses in BV-2 cells. Instead, lipoxygenase (LOX) inhibition, or more specifically LOX-12 and LOX-15, could significantly suppress ROS[slash]NO production in BV2 cells. Plants form the basis of traditional medicine in different civilizations throughout thousands of years. The use of herbal medicine was based on centuries of anecdotes and practitioners' experience. Recent incorporation of modern research methods to traditional medicinal investigation has shed light on the mechanism of action for many of these herbal products. Many medicinal plants and extracted compounds have been hypothesized or shown to ameliorate neurological conditions. In order to better understand the mechanism of action of botanical compounds on microglial activation pathway, an experiment was carried out in which mice were fed with control diet, elderberry diet and Sutherlandia diet for two months and followed by global cerebral ischemia by occlusion of the bilateral common carotid arteries. Mice fed with either elderberry or Sutherlandia diet demonstrated significant less motor deficits (by rotarod test). Histologic staining by cresyl violet stain showed significant decrease in neuronal cell death and decrease in microglia activation by either diet group. Immunohistochemical staining further showed colocalization of phospho-ERK and p47phox to microglial cells and decrease expression of the oxidative proteins in mice fed with either botanical diets.
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