A second explanation for the discrepancy between al explanation for this may be selleck bio that transporter function was altered by signaling pathways downstream of TLR4, resulting in for example, transporter dephosphorylation, deglycosylation, or tyrosine nitration. Indeed, activation of NF ��B in HT29 colon cancer cells decreases transport function of another drug transporter, human MRP3, via tyrosine nitration of the protein. This suggests that TLR4 signaling regulates microglial P glycoprotein activ ity to some extent, which is consistent with the fact that cytokines and NO are produced 6 to 24 hours later in the microglial response to LPS but fail to impact P glycoprotein functionsaquinavir accumulation in the current study.
The role of TLR4 in P glycoprotein regu lation is particularly Inhibitors,Modulators,Libraries relevant to pharmacotherapy in HIV, as there is increasing evidence that HIV proteins may activate macrophages through a TLR4 dependent pathway. In fact, a recent study shows that HIV1 Vpr tered P glycoprotein function and expression Inhibitors,Modulators,Libraries following LPS treatment is altered trafficking of P glycoprotein from intracellular stores to the cell surface. To actively efflux compounds, P glycoprotein must be correctly ori entated on the plasma membrane. In polarized cells such as brain capillary endothelium and choroid plexus epi thelia, proper routing of intracellular reserves of trans porter protein to the plasma membrane on the apical side is achieved through a series of complex molecular signaling events.
In brain capillaries, intracellular stores of P glycoprotein may cycle into and out of the endothe lial membranes following exposure to proinflammatory mediators as a short term adaptive compensation mech anism to cellular stresses. Inhibitors,Modulators,Libraries Mechanisms contributing to trafficking of drug transporter proteins within Inhibitors,Modulators,Libraries micro glia have not been identified. However, immunohisto chemical studies of P glycoprotein in microglia have localized the protein to both the plasma and nuclear membranes, demonstrating that intracellular compart ments for the protein do indeed exist and might be recruited in response to cellular stress. The interaction of LPS with microglia at the molecular level and subsequent signaling pathway activation have been well described elsewhere. At the cell surface level, LPS activation of TLR4, scavenger receptors Inhibitors,Modulators,Libraries and NADPH oxidase have all been implicated as initial events that initiate downstream intracellular signaling changes in microglia.
Inhibition of the scavenger recep tors and NADPH oxidase in the present studies did not attenuate the decrease in saquin avir accumulation following LPS challenge, whereas a TLR 4 neutralizing antibody caused partial attenuation. By decreasing TLR4 activity to a large extent using micro glia from TLR4 deficient mice, full attenuation of the changes in saquinavir transport in the presence new post of LPS in primary microglia was seen.