Background:
Aortic valve stenosis (AS) and insulin resistance have a high prevalence in western societies and prognostic relevance. Population based studies indicate that the progression of AS is increased in patients with diabetes mellitus. However, the impact of insulin resistance on AS and underlying cellular and molecular mechanisms are completely unknown. 

Hypothesis: We hypothesise that insulin resistance promotes inflammatory processes, myofibroblast transdifferentiation of valvular interstitial cells (VICs) and pro-calcific processes in the aortic valve before clinical manifestation of diabetes mellitus. 

Methods:
To this end, we investigated histological markers of inflammation, calcification and myofibroblast transdifferentiation in native aortic valves of New Zealand obese (NZO) mice with spontaneous insulin resistance and compared it to age-matched wildtype (WT) mice with induced experimental aortic valve stenosis. NZO mice were housed for 15-16 weeks. Male 12-week-old C57Bl/6 (WT) mice were subjected to either wire injury (WI) of the aortic valve to induce a moderate aortic valve stenosis, or a sham surgery. Successful induction of AS in WT was verified by echocardiographic analysis. Hearts of NZO mice with native valves and of WT mice four weeks after surgery were collected for histology. Cryosections of the aortic valve were stained with a) hematoxylin and eosin (H&E), b) anti-CD68 for macrophages, c) anti-vimentin, and d) anti-BMP2, anti-RUNX2. 

Results:
Histological analysis showed an increased aortic valve leaflet thickness in WT mice four weeks after WI compared to sham operated mice and even significantly more so in NZO mice compared to experimental aortic valve stenosis. The number of CD68 positive macrophages was elevated by tendency in native aortic valves of NZO mice as well as in WT mice four weeks after WI. Vimentin, which is increased in VICs after myofibroblast transdifferentiation, was significantly increased in NZO mice compared to WT with AS. In contrast, the calcification markers BMP2 and RUNX2 were only increased in WT with experimental aortic valve stenosis, but unchanged in NZO mice. 

Conclusion:
Insulin resistance in NZO is associated with thickening of the aortic valve. Increased number of macrophages and increased expression of vimentin in both models suggest that pathomechanisms of AS might already take place in the aortic valve of insulin resistant mice. The lacking calcification in the aortic valve of NZOs might reflect AS at an earlier stage in insulin resistance compared to the situation four weeks after WI. These observations shed light on the mechanisms by which insulin resistance might contribute to the onset and progression of AS in patients.