MicroRNAs and downstream Adipokines regulated by Adiponectin in vivo are novel targets for controlling adipose tissue inflammation

(eng) Adipose tissue (AT) has been recognized as an active secretory organ, which releases a number of bioactive peptides, collectively named adipokines. They play a central role in energy and vascular homeostasis as well as in immunity. Dysregulation of adipokines triggers the development of a low-grade pro-inflammatory state, which is considered to build the common soil for the development of obesity-linked disorders. Thus, resetting the immunological balance in obese AT is a fundamental therapeutic strategy for the metabolic syndrome. ApN has emerged as a master regulator of immune/inflammatory homeostasis. Yet, the autocrine/paracrine effects of ApN on AT inflammation have been poorly investigated. We have previously generated a transgenic mouse model allowing persistent and moderate overexpression of ApN (ApN-Overex) specifically in white AT. I therefore took advantage of this unique model to unravel the effects of ApN on AT secretory function. I confirmed that ApN regulated in vivo the secretion of downstream adipokines, decreasing those with pro-inflammatory properties, while enhancing those with anti-inflammatory effects. These changes were specific: they occurred before the emergence of any metabolic confounding factors (such as improvement of insulin action or decrease of fat mass). Moreover, a reverse profile of expression was observed for most adipokines in ApN-knockout (ApN-KO) mice. Thus ApN induced in vivo a shift of the immune balance in AT toward a less inflammatory phenotype. Moreover, this shift induced by ApN was associated with reduced activity of NF-κB and Extracellular Signal-Regulated kinases (ERK1/2), as well as increased activity/expression of AMPK in AT. MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression by inducing target mRNA degradation or blocking translation. Deregulation of miRNAs is closely associated with obesity-related metabolic disorders. I therefore used the same ApN-Overex mice to investigate whether miRNAs regulated by ApN contribute to the anti-inflammatory effects of ApN in AT and whether these miRNAs represent novel mechanisms for controlling AT inflammation. Four miRNAs were modified in AT of ApN-Overex mice. Expression of miR532-5p and miR1983 was down-regulated, while that of miR883b-5p and miR1934 was up-regulated. miR883b-5p was identified by computational analysis as being involved in inflammatory pathways. By using gain-of or loss-of function approaches, I further validated that miR883b-5p repressed the lipopolysaccharide (LPS) facilitator, LPS-binding protein (LBP) in 3T3-F442A cells. miR883b-5p blockade also abolished the protective effects of ApN on induction of pro-inflammatory adipokines. These data were recapitulated in de novo AT (formed from engineered 3T3-F442A preadipocytes transplanted in nude mice) where miR883b-5p silencing induced LBP production and tissue inflammation. Eventually, miR883b-5p expression was down-regulated in AT of obese subjects, concomitantly with reduced ApN expression. Altogether, these data suggest that miR883b-5p may be an important mediator of the anti-inflammatory action of ApN in adipocytes. These newly identified downstream adipokines and miRNAs may open new therapeutic perspectives for the management of metabolic syndrome.