Pattern Recognition Receptors-initiated Innate Antiviral Response In Mouse Adipose Cells

Background and objectives:Increasing evidence indicates that adipose tissue is an immunoregulatory organ. Although wide range of viruses can infect adipose tissues, innate antiviral response of adipose cells has not been investigated. This study focused on innate antiviral response in mouse adipose cells through the activation of RNA and DN A virus sensors.Materials and methods:Preadipocytes cells and mature adipocytes were used in this study. The cells were stimulated with synthetic viral RNA analog poly(I:C) and hepes simplex viral DNA (HSV60). Western blot, immunohistochemistry, immunofluorescence staining were used to analyze the location and expression of proteins. The mRNA level was examined using qRT-PCR. The cytokine production was measured using ELISA.Results:Viral RNA sensors, including Toll-like receptor3(TLR3), melanoma differentiation-associated antigen5(MDA5), and retinoic acid-inducible gene Ⅰ (RIG-I), are constitutively expressed in primary preadipocytes and adipocytes. Poly(I:C), a common agonist of TLR3, MDA5and RIG-Ⅰ, induced the expression of type Ⅰ interferons (IFN-α and IFN-β) through the activation of IFN-regulatory factor3, and upregulated pro-inflammatory factors (TNF-α and IL-6) through the activation of nuclear factor kappa B. Moreover, poly(I:C) induced the expression of multiple antiviral proteins, including IFN-stimulating gene15,2’5’-oligoadenylate synthetase and Mx GTPase1. The poly(I:C)-induced innate antiviral response was reduced by TLR3deficiency and knockdown of MDA5or RIG-I. Poly(I:C) also inhibited the differentiation of preadipocytes to adipocytes, and suppressed the expression of leptin, adiponectin, and resistin in mature adipocytes. We also investigated the function of viral DNA sensors in preadipocytes. p204and stimulator of interferon genes (STING) were constitutively expressed in preadipocytes. HSV-60, a functional ligand of p204, induced the expression of type I interferons (IFN-α and IFN-β) through the activation of IFN-regulating factor3. Moreover, the HSV60induced antiviral protein expression in preadipocytes. HSV60also inhibited the differentiation of preadipocytes to mature adipocytes and suppressed the expression of several adipokines, including leptin, adiponectin, and resistin in the mature adipocytes. The results demonstrated that adipose cells are equipped with innate antiviral system, which may modulate the function of adipocytes. Conclusions:PRRs that recognize RNA and DNA viruses are constitutively expressed in adipocytes. These PRRs initiated innate antiviral response to mimic viral stimulation, which inhibited the diffrentiation of preadipocytes and the expression of leptin, adiponectin, and resistin. The results revealed the antiviral function of the adipose tissue.