1Universitätsklinikum Giessen und Marburg GmbH Klinik für Kardiologie, Angiologie und internistische Intensivmedizin Marburg, Deutschland; 2Philipps-Universität Marburg Kardiologie Marburg, Deutschland; 3Karolinska University Hospital Dept. of Cardiology Stockholm, Schweden; 4Universitätsklinikum Gießen und Marburg GmbH Kardiologie Marburg, Deutschland
Aims: The role of the cytosolic pattern recognition receptors nucleotide-binding oligomerization domain-containing protein (Nod) 1 and 2 in atherosclerosis and diabetes under experimental conditions of hyperlipidemia/hypercholesterolemia have been well studied in recent years. We here identified a crucial role of Nod1 and Nod2 under normocholesterolemic/normolipidemic conditions for metabolic processes and body weight control.
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. The body weight was determined over time and after 22 weeks, organs such as inguinal white adipose tissue and liver were harvested, weighed, and preserved. Paraffin sections were prepared from adipose tissue and stained with Hematoxylin/Eosin. Liver cryosections were prepared and stained with periodic acid Schiff reagent and Sirius Red. Plasma and liver lipid profile was measured by fast protein liquid chromatography. Plasma insulin and leptin levels were assessed through enzyme-linked immunosorbent assay. Liver and adipose tissue gene expression were 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). Organ weights of the liver (1.48±0.22 vs. 1.18±0.33 g) and especially adipose tissue (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-deficiency increased adipocyte size and adipoflammation. Nod1/2-KO mice showed increased hepatic triglyceride levels, lipid accumulation as well as increased glycogen content, increased fasting plasma glucose levels, and slightly impaired insulin tolerance but no signs of liver fibrosis. Furthermore, NOD1/2-deficiency led to increased fasting plasma insulin and leptin levels. Mechanistically, Nod1/2-KO mice showed increased expression of hepatic genes for fatty acid synthesis and gluconeogenesis as well as adipocyte lipolysis enzymes.
Conclusion: We identified Nod1 and Nod2 as regulators of body weight and glucose metabolism independent of hyperlipidemia/hypercholesterolemia conditions, possibly through changes in hepatic and adipose tissue gene expression and the gut microbiome.