Off-target genomic effects in MRP8-Cre driver mice complicate its use in weight gain and metabolic studies

BackgroundThromboinflammation of adipose tissue involves accumulation of pro-fibrinogenic factors to adipose tissue in obesity, which promotes immune cell infiltration, affects weight gain and can lead to metabolic dysfunction. The role of neutrophil genes in inflammation are frequently investigated using MRP8-Cre mice to generate neutrophil-specific knockouts. Recent study demonstrated that MRP8-Cre mice have off-target deletions in Serpine1 and Ap1s1 genes. Serpine1, encoding plasminogen activator inhibitor-1, is a key anti-fibrinolytic factor linked to thromboinflammation and metabolic dysfunctions in obesity. In this study, we provide evidence suggesting a critical limitation in using MRP8-Cre model to study adipose tissue, weight-related dysfunctions and/or metabolic disorders. MethodsMRP8-Cre and F13a1-/-MRP8 mice were placed on either control diet or high-fat diet for 16 weeks, with body weight monitored weekly. The expression of Serpine 1, Ap1s1 and Adgre1 (macrophage marker) genes in inguinal and epididymal adipose tissues were analyzed using qRT-PCR and compared to the wild-type mice. ResultsMRP8-Cre shows no Serpine1 or Ap1s1 expression in inguinal and epididymal adipose tissues. MRP8-Cre mouse is resistant to weight gain on obesogenic diet and does not show macrophage marker in adipose tissue compared to control obesity model. The resistance to weight gain translates to a neutrophil knockout model, F13a1-/-MRP8 that was not expected to show resistance to weight gain as its global knockout does not exhibit this phenotype. ConclusionOur work suggests that MRP8-Cre model may not be suitable to investigate metabolic outcomes of neutrophil genes, or pathologies that have underlying etiology in thomboinflammation.