NO CODING RNAs IN MACROPHAGE POLARIZATION: THE RELEVANCE OF THE "JUNK" RNA

Abstract Form the central dogma of the biology formulated by Crick in 1958, to the detection of “junk RNA”, a new prospective has been open. Macrophages are essential cell of the innate immunity system important in onset and resolve inflammation. Moreover they are important in the cross-talk with adaptive immunology. It is also clear that macrophages are involved in many chronic diseases such as atherosclerosis, asthma, rheumatoid arthritis. In these pathologies there is an anomalous prolongation/amplification of the macrophage challenge to lead homeostasis. In this landscape favor macrophage activation and re-programming. Mantovani and colleagues have schematically categorized macrophages in “classical” (M1) activated, triggered with microbial stimuli (e.g. LPS) alone or together with the TLR eliciting; and “alternative” (M2) cell types, activated by IL-4/IL-13. The identification of the underlying molecular mechanisms on the base of this process may suggest new approaches to interfere with chronic inflammation and other inflammatory disease, such as cancer. The aim of this presented work was to characterize the epigenetic mechanism involved in macrophage polarization. To better elucidate this purpose the thesis was divided in three macro chapter: • MicroRNA-135b: the pivot of the macrophage polarization balance; • The “junk” RNA controlled by glucocorticoids: miR-135b and its host gene BLACAT1; • MicroRNA-135b in gouty arthritis. Overall, we identified a specific miRNome in human classic and alternative polarized macrophages (69 differential expressed miRNAs among the subsets). In addition, we pointed out the impact of miR-135b a de novo expressed miRNA in M1 macrophages, and for the first time associated with macrophages in an inflammatory diseases such as gouty arthritis. Indeed we demonstrated that miR-135b locus is activated by the inflammatory stimulus, LPS, which discharge the repressor complex polycomb2. Although, we can classified miR-135 as M1-associated or induced, which damps M2 phenotype in favor of the M1 thru the targeting of important the transcription factor, c-MYC, STAT6 and KLF4, sustaining the inflammation. In addition miR-135b expression is inhibited by the anti-inflammatory cytokine IL-10, to highlight its pro-inflammatory role; the same results was assess for miR-155. We have shown in the model of gouty arthritis, miR-135b is induced during the progression of the inflammation by macrophages. However it provides a negative feedback to limit excessive macrophage response to MSU crystal, thru the targeting of the IL-1β pathway. These results confirm the relevance of miR-135b as an important hinge of macrophage polarity. At the light of these observations, the identification of the underlying process that regulates the expression of miR-135b will be essential. miR-135b is located in the intron of the lncRNA, BLACAT1. We glimpsed that the induction of miR-135b and BLACAT1 is not correlated; on the contrary BLACAT1 is induced by anti-inflammatory stimulation, influencing miR-135b. Although we can speculate a novel type of regulation beyond IL-10, used by the macrophages to control the expression of this miRNA. Probably with the action of the MCP-induced protein 1 (MCPIP1), which is induced downstream LPS and IL-1β pathway and has been shown to suppress miR-135b biosynthesis in cancer.