Background and objectives: Hepatic steatosis and inflammation are key characteristics of non-alcoholic fatty liver disease (NAFLD). However, whether and how hepatic steatosis and liver inflammation are differentially regulated remains to be elucidated. Considering that disruption of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (Pfkfb3/iPfk2) dissociates fat deposition and inflammation, the present study examined a role for Pfkfb3/iPfk2 in hematopoietic cells in regulating hepatic steatosis and inflammation in mice.
Methods: Pfkfb3-disrupted (Pfkfb3 +/-) mice and wild-type (WT) littermates were fed a high-fat diet (HFD) and examined for NAFLD phenotype. Also, bone marrow cells isolated from Pfkfb3 +/- mice and WT mice were differentiated into macrophages for analysis of macrophage activation status and for bone marrow transplantation (BMT) to generate chimeric (WT/BMT- Pfkfb3 +/-) mice in which Pfkfb3 was disrupted only in hematopoietic cells and control chimeric (WT/BMT-WT) mice. The latter were also fed an HFD and examined for NAFLD phenotype. In vitro, hepatocytes were co-cultured with bone marrow-derived macrophages and examined for hepatocyte fat deposition and proinflammatory responses.
Results: After the feeding period, HFD-fed Pfkfb3 +/- mice displayed increased severity of liver inflammation in the absence of hepatic steatosis compared with HFD-fed WT mice. When inflammatory activation was analyzed, Pfkfb3 +/- macrophages revealed increased proinflammatory activation and decreased anti-proinflammatory activation. When NAFLD phenotype was analyzed in the chimeric mice, WT/BMT-Pfkfb3 +/- mice displayed increases in the severity of HFD-induced hepatic steatosis and inflammation compared with WT/BMT-WT mice. At the cellular level, hepatocytes co-cultured with Pfkfb3 +/- macrophages revealed increased fat deposition and proinflammatory responses compared with hepatocytes co-cultured with WT macrophages.
Conclusions: Pfkfb3 disruption only in hematopoietic cells exacerbates HFD-induced hepatic steatosis and inflammation whereas the Pfkfb3/iPfk2 in nonhematopoietic cells appeared to be needed for HFD feeding to induce hepatic steatosis. As such, the Pfkfb3/iPfk2 plays a unique role in regulating NAFLD pathophysiology.
Keywords: 6-Phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (Pfkfb3/iPfk2); Hematopoietic cells; Hepatic steatosis; Inflammation; Macrophages.