Macrophage migration inhibitory factor (MIF) is a cytokine that is increased in obesity and contributes to metabolic dysfunction. Our present study describes a novel mechanism by which fatty acids activate non-immune cells to increase MIF secretion in adipose tissue, initiating cross-talk between preadipocytes and adipocytes. High fatty acids specifically induce protease-activated receptor 2 (PAR2) activation in preadipocytes, which downregulates pref-1 expression and release. Preadipocyte factor 1 (Pref-1) has an autocrine-paracrine action to inhibit the release of MIF from both preadipocytes and adipocytes. Thus, the loss of Pref-1 secretion during high fat feeding is responsible in part for both increased MIF secretion in adipose tissue and the rise in plasma MIF levels that ensues. The physiological consequences are most evident in adipose tissue. Genetic deletion of Par2 confirms the importance of this mechanism in mice, protecting against high fat diet-induced metabolic dysfunction. Importantly, this novel mechanism is also operative in adipose tissue from obese human subjects. These results provide the scientific rationale to consider whether strategies to either block Par2 expression or augment Pref-1 secretion might improve metabolic health in obesity or type 2 diabetes. Disclosure Y. Huang: None. L. Chen: None. Y. Qi: None. D. Qi: None.

Olanzapine is one of the first-line antipsychotic medications but it usually induces metabolic side effects, characterized by obesity. We previously indicated that olanzapine leads to hyperphagia through the effects of a proinflammatory cytokine, macrophage migration inhibitory factor (MIF) in the hypothalamus. However, whether olanzapine's upregulated peripheral MIF could affect the central mechanism is currently unknown. Our present study found that olanzapine increases ectopic expression of dopamine receptor 1 (DRD1) in adipocytes which relatively upregulates MIF expression and release through a PKA/CREB signaling pathway. In global MIF knockout mice, MIF accumulation appears in the hypothalamus following peripheral injection of recombinant MIF proteins, suggesting that peripheral MIF indeed travels to the hypothalamus. Mif Lung Tg mice (MIF overexpression in the lung) with increased circulating MIF levels had hyperphagia and activation of the CaMKKβ/AMPK/AgRP signaling pathway in the hypothalamus. Overall, our study for the first time proved that adipose-derived MIF is a crucial factor in regulating metabolic side effects induced by olanzapine. Disclosure X.Chen: None. Y.Huang: None. Y.Qi: None. L.Chen: None. L.Li: None. P.Gao: None. D.Cui: None. D.Qi: None. Funding National Sciences and Engineering Research Council of Canada (RGPIN-2017-04542); Canadian Institutes of Health Research (PJT-156116); China Scholarship Council (202106230212)

Lipoprotein lipase (LPL) is a key enzyme that hydrolyzes circulating triglycerides to release fatty acid (FA). In adipose tissue, LPL is required for lipid storage. However, it is currently unknown whether alteration of LPL in white adipose tissue (WAT) contributes to the development of hypertriglyceridemia. Our present study indicated that WAT isolated from human obese patients have increased expression of PAR2 which is negatively associated with LPL gene. The reduced LPL expression is also negatively correlated with increased plasma TG levels, suggesting that adipose PAR2 may modulate hyperlipidemia through downregulating LPL. In mice, aging and high palmitic oil diet significantly increased PAR2 expression in adipose tissue which was associated with high plasma MIF levels. PAR2 deficiency attenuates the rise of MIF, suggesting a key role of PAR2 in regulating adipose MIF release. MIF reduced LPL expression and activity in adipocytes. In a MIF overexpressed animal model (Mif lung Tg), high circulating MIF levels inhibited adipose LPL which was associated with increased plasma triglyceride but not fatty acid. Following high palmitic oil diet feeding, adipose LPL expression and activity were also reduced, and this reduction was reversed in PAR2 knockout mice. Interestingly, PAR2 mediated LPL in adipose tissue regulates hypertriglyceridemia through controlling adipocyte lipid storage. In Par2-/- mice, recombinant MIF perfusion recovered high plasma MIF levels, which decreased LPL and attenuated adipocyte lipid storage leading to hypertriglyceridemia. These data together suggest that the downregulation of adipose LPL by PAR2/MIF is an important mechanism for the development of hypertriglyceridemia. Disclosure Y.Huang: None. L.Li: None. L.Chen: None. X.Chen: None. P.Gao: None. Y.Qi: None. D.Qi: None. Funding Canadian Institutes of Health Research (PJT156116)

Nonalcoholic fatty liver disease (NAFLD) is associated with metabolic dysfunctions, such as obesity. Macrophage migration inhibitory factor (MIF), a pro-cytokine, was also identified to regulate NAFLD, but the molecular mechanisms remain unclear. We presently indicated that MIF has a non-inflammatory effect on triggering NAFLD through upregulating its cell membrane receptor, CD74. MIF increased CD74 protein rather than gene expression in liver cells in a time-dependent manner. That was not associated with any changes in the expression of pro-inflammatory factors, such as TNF-α, IL-6 and IL-1β. In a MIF overexpressed animal model (Mif lung Tg), high circulating MIF levels increased hepatic CD74 proteins but not genes in the absence of inflammation in the liver. High fat diet also increased circulating MIF levels leading to an upregulation of hepatic CD74. All these animal models with high circulating MIF and hepatic CD74 were accompanied with steatosis and fibrosis in the liver. These alterations could be reversed by either MIF neutralization or MIF knockout. Caspase 4 facilitates the degradation of CD74. MIF endocytosis inhibited caspase 4 cleavage and activation. Thus, inhibition of MIF upregulated cleaved caspase 4 leading to a degradation in CD74. Overall, our findings indicate that MIF stabilizes CD74 through suppressing caspase 4 and this may be an important mechanism in regulating NAFLD in the absence of inflammation. Disclosure L. Chen: None. L. Li: None. Y. Huang: None. X. Chen: None. Y. Qi: None. H. Tong: None. H. Wu: None. D. Qi: None. Funding Canadian Institutes of Health Research (PJT156116); Research and Development Corporation; National Sciences and Engineering Research Council of Canada (RGPIN-2017-04542); National Institutes of Health (AR-078334); China Scholarship Council (to L.C., Y.H., L.L.)

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