Deletion of complement factor 5 amplifies glucose intolerance in obese male but not female mice.

Complement factor 5 of the innate immune system generates C5a and C5b ligands, which initiate inflammatory and cell lysis events, respectively. C5 activation has been linked with obesity-associated metabolic disorders; however, whether it has a causative role is unclear. We generated a C5 null (C5) mouse using CRISPR-Cas9 gene editing to determine whether loss of C5 improves obesity-linked metabolic dysfunction. Generation of a new mouse model was prompted in part by the observation of off-target gene mutations in commercially available C5 lines. Male and female wild-type (WT), heterozygous (Het), and C5 mice were fed low-fat diet (LFD) or high-fat diet (HFD) for 22 wk. Body weight gain did not differ between genotypes on LFD or HFD. In lean animals, male C5 mice had similar glucose tolerance compared with WT controls; however, in obese conditions, glucose tolerance was worsened in C5 compared with controls. In contrast, female mice did not exhibit differences in glucose tolerance between genotypes under either dietary paradigm. Fasting insulin was not different between genotypes, whereas diet-induced obese male C5 mice had lower fed insulin concentrations compared with WT controls. No differences in adipose tissue inflammation or adipocyte size were identified between groups. Similarly, susceptibility to fatty liver and hepatic inflammation was similar between WT and C5 mice. However, the systemic cytokine response to acute endotoxin exposure was decreased in C5 mice. Together, these data suggest that loss of C5 worsens glucose tolerance in obese male but not female mice. Additional work is required to pinpoint the mechanisms by which loss of C5 amplifies glucose intolerance in obesity. We generated a new mouse model of complement factor 5 deficiency. This work was prompted by a need for improved transgenic mouse lines of C5, due to off-target gene mutations. We find that loss of C5 worsens glucose tolerance in a sex-dependent manner. Though the mechanisms evoking glucose intolerance are not clear, we are confident this model will be useful in interrogating complement activation in obesity-associated diseases.