Aims: The role of the cytosolic pattern recognition receptors nucleotide-binding oligomerization domain-containing protein (Nod) 1 and 2 in atherosclerosis and metabolic diseases such as diabetes have been well studied in recent years. However, these studies were performed under conditions of hyperlipidemia/hypercholesterolemia on high-fat diets. The aim of this study is to investigate the role of Nod1/2 under normocholesterolemic/normolipidemic conditions.

Methods: Nod1 and Nod2 knockout mice (Nod1/2-KO) have been generated on a low-density lipoprotein receptor knockout background. Mice were fed a standard maintenance diet (chow diet) for 22 weeks. Glucose tolerance and insulin resistance were assessed in tail vein blood with a glucometer. Body weight was determined over time and after 22 weeks, organs such as inguinal white adipose tissue and liver were harvested. Micro sections of paraffin-embedded adipose tissue were stained with hematoxylin/eosin. Plasma lipid profile was determined by fast protein liquid chromatography, liver lipid content biochemically. Liver gene expression was analyzed by real-time PCR and gut microbiota composition by 3rd generation sequencing.

Results: Nod1/2-KO gained significantly more body weight than control mice from week 12 onwards (36.0±4.8 vs 27.8±2.7 g at week 22). Liver (1.48±0.22 vs. 1.18±0.33 g) and especially adipose tissue weight (1.24±0.35 vs. 0.40±0.15 g), as well as adipocyte size (5075±380 vs. 1945±123 µm²), were strongly increased in Nod1/2 KO mice. The increase in body and liver/adipose tissue weight was observed in both male and female mice. Nod1/2-KO mice showed increased hepatic triglyceride levels, increased fasting plasma glucose levels, and slightly impaired insulin tolerance. In addition, Nod1/2-KO mice showed increased expression of hepatic stearoyl-CoA desaturase (Scd)-1 and phosphoenolpyruvate carboxykinase (Pck)-1 and altered gut microbiome composition.

Conclusion: We identified Nod1 and Nod2 as regulators of body weight and glucose metabolism independent of hyperlipidemia/hypercholesterolemia, conceivably mediated by changes in hepatic gene expression and gut microbiome.