Background: Pulmonary hypertension (PH) is associated with high morbidity and mortality. Prognosis is determined by occurrence of right ventricular (RV) failure, a key characteristic of PH. Currently, there is no treatment for RV failure, in part due to lack of mechanistic understanding of the development of RV failure. Further research into the development of RV failure is therefore imperative.
Exposure to hypoxic conditions is used as a model for PH and RV failure in rats, however, recent studies demonstrated that mice exhibit less severe pulmonary vascular remodeling when exposed to chronic hypoxia compared to rats. Additionally it has previously been shown that adding a low copper diet to pulmonary artery banding (PAB) leads to increased RV fibrosis and dilation due to capillary rarefaction.
Here we hypothesize that adding a low-copper diet to chronic hypoxia in mice reinforces their individual effect and that the combination of mild pulmonary vascular remodeling and capillary rarefaction, induces RV failure.
Methods: Six week old mice were subjected to normoxia (N; 21% O2) or hypoxia (H; 10% O2) during a period of 8 weeks. Additionally, both experimental groups received either normal chow diet (Cu+) or a copper depleted (Cu-) diet. Cardiac function in these mice was assessed by echocardiography/MRI. Cardiac ventricular tissue was analyzed by histology and immunohistochemistry, and cardiac stress marker expression levels were determined by qPCR.
Results: Exposure to chronic hypoxia led to right ventricular hypertrophic growth when compared to normoxia, indicated by a significant increase in Fulton index (N/Cu+ 0.23 ± 0.01 vs. H/Cu+ 0.39 ± 0.02; H/Cu- 0.40±0.06 ; p< 0.05), as well as a significant decrease in RV ejection fraction at 8 weeks (N/Cu+ 71.7 ± 2.6% vs. H/Cu+ 58.8±3.3; H/Cu- 60.0 ± 4.2%, p<0.05). There was however, no further increase in Fulton index after adding a copper deficient diet to hypoxia treatment (H/Cu- 0.40± 0.06), nor was there a further decrease in ejection fraction. In addition, there was a trend towards an increase in cell size in the hypoxia groups, when compared to the N/Cu+ group, correlating with the observed changes in Fulton index and RV ejection fraction.
Conclusion: Eight weeks of 10% hypoxia is sufficient to initiate RV hypertrophy and subsequent RV failure. Adding a low copper diet to chronic hypoxia, however, does not further exacerbate right ventricular remodeling, showing that the combination of hypoxia with a copper depleted diet is not an adequate model for RV failure in mice.