Anaphylatoxin Receptors C3aR and C5aR1 Are Important Factors That Influence the Impact of Ethanol on the Adipose Secretome

Abstract

Background and aims: Chronic ethanol exposure results in inflammation in adipose tissue; this response is associated with activation of complement as well as the development of alcohol-related liver disease (ALD). Adipose communicates with other organs, including liver, via the release of soluble mediators, such as adipokines and cytokines, characterized as the “adipose secretome.” Here we investigated the role of the anaphaylatoxin receptors C3aR and C5aR1 in the development of adipose tissue inflammation and regulation of the adipose secretome in murine ALD (mALD).Methods: Wild-type C57BL/6 (WT), C3aR−/−, and C5aR1−/− mice were fed Lieber-DeCarli ethanol diet for 25 days (6% v/v, 32% kcal) or isocaloric control diets; indicators of inflammation and injury were assessed in gonadal adipose tissue. The adipose secretome was characterized in isolated adipocytes and stromal vascular cells.Results: Ethanol feeding increased the expression of adipokines, chemokines and leukocyte markers in gonadal adipose tissue from WT mice; C3aR−/− were partially protected while C5aR1−/− mice were completely protected. In contrast, induction of CYP2E1 and accumulation of TUNEL-positive cells in adipose in response to ethanol feeding was independent of genotype. Bone marrow chimeras, generated with WT and C5aR1−/− mice, revealed C5aR1 expression on non-myeloid cells, likely to be adipocytes, contributed to ethanol-induced adipose inflammation. Chronic ethanol feeding regulated both the quantity and distribution of adipokines secreted from adipocytes in a C5aR1-dependent mechanism. In WT mice, chronic ethanol feeding induced a predominant release of pro-inflammatory adipokines from adipocytes, while the adipose secretome from C5aR1−/− mice was characterized by an anti-inflammatory/protective profile. Further, the cargo of adipocyte-derived extracellular vesicles (EVs) was distinct from the soluble secretome; in WT EVs, ethanol increased the abundance of pro-inflammatory mediators while EV cargo from C5aR1−/− adipocytes contained a greater diversity and more robust expression of adipokines.Conclusions: C3aR and C5aR1 are potent regulators of ethanol-induced adipose inflammation in mALD. C5aR1 modulated the impact of chronic ethanol on the content of the adipose secretome, as well as influencing the cargo of an extensive array of adipokines from adipocyte-derived EVs. Taken together, our data demonstrate that C5aR1 contributes to ethanol-mediated changes in the adipose secretome, likely contributing to intra-organ injury in ALD.

Inflammatory pathways in alcoholic steatohepatitis

“…59 Ethanol also modifies the adipokine cargo of EVs released by adipocytes. 60 These ethanol-induced changes in the metabolic and immune function of adipose tissue all contribute to inflammation and injury in the liver.…”

“…80,81 Further, it is clear that both the anaphylatoxin receptors, complement C3a receptor 1 (C3AR1) and complement C5a receptor 1 (C5AR1), are important for ethanolinduced complement activation to progress to liver inflammation and injury. 60 As with many innate immune functions, while complement activation is pro-inflammatory, it is also required for resolution of injury. For example, complement activation via the alternative pathway is critical to the removal of injured and dying hepatocytes in models of both fibrosis and early ASH.…”

“…90,91 Interestingly, recent data suggest an interaction between complement C5AR1 and chronic ethanol in determining the adipokine cargo of EVs released from adipocytes. 60 Adipocyte-derived EVs are likely a mechanism for the crosstalk between adipose tissue and the liver in ALD.…”

Oxidized Low-Density Lipoprotein Drives Dysfunction of the Liver Lymphatic System

“…31 This increase of lymphatic density in murine livers during disease was independent of disease etiology (MDR2-/-, Lieber-DeCarli diet and high-fat, lowcholesterol diet) ( Figure 2E and F). 33 Using the HFHC diet model, we found that after 17-24 weeks on the diet, the mice developed steatosis and inflammation, increased aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and increased total cholesterol, high-density lipoprotein, and LDL ( Figure 3A-D). As our model of NASH demonstrates high liver LDL levels, these findings are also consistent with increased LDL exposure causing lymphatic-specific gene downregulation ( Figure 2D).…”

From COVID-19 to clot: the involvement of the complement system

“…Moreover, C3b contributes to the configuration of the C5 convertases that cleave C5, leading to the production of the anaphylatoxin C5a that attracts and activates inflammatory leukocytes, and C5b (Fromell et al, 2020). C5a directly reciprocates with its C5aR on endothelial cells (McCullough et al, 2018), and produces intense changes of the physiologically thrombo-resistant endothelium, such as upregulation of tissue factor and profound decrease of thrombo-modulin, leading to platelet aggregation and adhesion (Gasque et al,1997). As for C5b, it instigates the terminal events of complement activation, resulting in the formation of the membrane-attack complex (MAC or C5b-9 complex), which implants itself into cell Angiotensin-converting enzyme (ACE2) plays a crucial role in the initiation of COVID-19 infection by attaching to the endothelial cells and hence having the domino effect on the infection and defense processes including the complement system.…”