Mechanistically GW treatment modulated cytokine expression
Mechanistically, GW2580 treatment modulated cytokine expression within the kidney. We noted a decrease in the levels of TNF, MCP-1, IL-1β, IL-27, and GM-CSF in GW2580 treated mice. Decreased levels of these proinflammatory cytokines likely contributed to the attenuated proteinuria and improved renal functioning. In our previous study in an inducible model of LN, we similarly noted that GW2580 treatment decreased kidney cytokine expression , underscoring the importance of macrophage associated cytokines in LN pathogenesis. Lupus patients exhibit neuropsychiatric manifestations that can occur at any stage of disease, even before the onset of other organ damage , . Thus, NPSLE is believed to be a primary manifestation of SLE . Cytokines are viewed as pivotal mediators in NPSLE , while microglia are an important source of cytokines in the brain. The use of GW2580 to deplete microglia allowed us to assess neurobehavioral manifestations after the administration of the monospecific kinase inhibitor. Excitingly, we found GW2580 treated mice exhibited significantly less depression-like behavior. Macrophages have been implicated as potential effector cells in the pathogenesis of various forms of depression, and it is thought macrophages may contribute to depression via expression of proinflammatory cytokines , . Cytokine dysregulation has been proven to be directly associated with depression by numerous studies , . Intracerebroventricular injection of monocyte-derived cytokines such as TWEAK and IL-6 directly result in depression-like behavior in vivo , . In addition, systemic inflammatory mediators may also induce negative behavior outcomes by accessing the R-848 via the BBB, or directly acting on the vagus nerve . We found that GW2580 treatment decreased the levels of several proinflammatory cytokines in the brain, including TNF, IL-12p70, IL-1β, IL-10, and IL-27. Therefore, considering the known contribution of cytokines to depression, our data in this paper highlight a potential mechanism underlying the attenuated depression-like phenotype in GW2580 treated mice. However, we did not find that GW2580 affects visual memory, suggesting perhaps that different mechanisms may account for individual behavioral phenotypes in the MRL/lpr strain. Indeed, MRL/lpr mice display depression-like behavior as early as 5weeks of age, while spatial memory deficits do not occur until 16weeks of age . In addition, different sub-regions of the brain are involved in depression and cognitive function. Furthermore, depleting microglia in healthy C57/Bl6 mice does not affect normal cognition suggesting that this function may not be not dependent on microglia , as would be consistent with our results. Although we expected that mice receiving the GW2580 compound would exhibit decreased microglia number and/or activation in the brain, we actually observed increased IBA-1 staining intensity in the GW2580 treated group. This perhaps can be explained by the fact that the brains were extracted 2weeks after the treatment ended, and by that time point the microglial population may have already recovered. Indeed, Elmore et al. also found that microglia can rapidly repopulate one week after the cessation of treatment with PLX3397 , a drug with a similar mechanism of action in its inhibition of CSF-1R. Indeed, the cessation of GW2580 two weeks prior to neurobehavioral testing may also be an alternative explanation why treated mice exhibited no improvement in spatial memory deficits. In addition, we did not find any histopathological differences between the GW2580 and control treated group, indicating that these NPSLE-associated phenomena are mediated by other factors besides, or in addition to, microglia. Analyzing the timing of microglia depletion and repopulation and any differential effect on microglial sub-phenotypes (M1 or M2), as well as cytokine expression during or right after cessation of the GW2580 treatment, will be a priority in future studies.