| A specific G-protein coupled receptor (GPCR) system has been identified, which is activated by compounds isolated from the plant Cannabis sativa , including Delta9-tetrahydrocannabinol (THC). Two unique gene products encode for different GPCR's, which interact with THC and a group of related compounds collectively know as 'cannabinoids'. Signaling through the peripheral cannabinoid receptor (CB2) enhances proliferative responses to growth factors, and may be involved in maturation of leukoid cells. Conversely, activation of the CB1 isoform of the cannabinoid receptor is implicated in the induction of apoptosis.; The distribution of cannabinoid receptors lead us to hypothesize that the resident immune cell of the central nervous system, the microglia, would exhibit cannabinoid receptor dependent signal transduction, and that microglial response to growth factors is modulated by concurrent exposure to cannabinoids through a receptor dependent mechanism. To determine the validity of this premise, we established a non-virally transformed rat microglial cell line model, determined the effects of cannabinoid exposure on cell cycle progression following stimulation of the microglial cell lines with a specific growth factor, macrophage colony stimulating factor (CSF-1), and evaluated the involvement of a cannabinoid receptor signal cascade in cell proliferation.; The established rat microglia cell lines (RTMGL), exhibited functional characteristics of microglia. Two clonal lines were studied in detail. When incubated with the gram-negative bacterial cell wall constituent lipopolysaccharide, the two RTMGL cell lines demonstrated a dose dependent production of TNF-alpha, and an increase in nitric oxide synthase activity. The microglial cell lines also retained cytochemical markers of microglia including positive staining with Griffonia simplicifolia isolectin B4, and the absence of glial fibrillary acidic protein expression as determined by immunocytochemistry. Importantly, RTMGL express CB2 receptor message and protein, together with low levels of CB1 receptor transcript. These data indicate a specific mechanism through which cannabinoids can initiate intracellular signal cascades in microglia.; One of the endocannabinoids, 2-arachidonylglycerol (2-AG) caused a concentration dependent increase in CSF-1 stimulated cell cycle progression. This enhancement was not seen with another endocannabinoid, N-arachidonylethanolamine (anandamide).; In contrast, we have found that the plant-derived cannabinoids, THC and cannabidiol (CBD) cause significant inhibition of S-phase progression as shown by a decrease in [3H] thymidine incorporation into the DNA. Potent effects are observed with THC exhibiting an IC50 value of 146 nM and a value of 171 nM for CBD. (Abstract shortened by UMI.)... |
