The role of endothelial PRDM16 in a mouse model of experimental pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but severe cardiopulmonary disease characterized by pulmonary vascular remodeling resulting in increased pulmonary vascular resistance, right heart failure, and death, if left untreated. Current treatments only provide palliative relief, underscoring the need to explore novel targets to cure PAH. We demonstrated that endothelial cell (EC) but not smooth muscle cell PRDM16, an arterial-restricted transcription factor, is indispensable for arterial flow recovery upon ischemia in the systemic circulation by preserving arterial endothelial function in mice. Therefore, PRDM16 appears as an appealing, yet unexplored target.

Because the endothelium plays a crucial role in both the initiation and progression of PAH, we hypothesized that endothelial PRDM16 deficiency would exacerbate experimental PAH.

To implement the sugen/hypoxia (SuHx) experimental mouse model of PAH in our lab, control Prdm16fl/fl mice (referred to as EC-Prdm16+/+) mice were exposed to Su/Hx, Su alone, Hx alone, or a vehicle for three weeks. To study the role of endothelial PRDM16 in PH, we subjected EC-Prdm16-/- and control EC-Prdm16+/+ littermates to hypoxia alone for 1 or 3 weeks. At the end of the experiment, right ventricular systolic pressure (RVSP) was assessed by right heart catheterization, RV hypertrophy (RVH) was evaluated by fulton index and muscularization of peripheral pulmonary vessels was determined by lung histology.

The first goal was to implement the SuHx experimental mouse model of PAH in our lab. Unexpectedly, RVSP and RVH were similar in EC-Prdm16+/+ mice exposed to SuHx or hypoxia alone, suggesting that in our hands mice exposed to SuHx did not develop more severe pulmonary hypertension (PH) compared to mice exposed to hypoxia alone (Fig. 1A,B). Therefore, to study the role of endothelial PRDM16 in PH, we subjected both EC-Prdm16-/- and EC-Prdm16+/+ to hypoxia for 1 or 3 weeks. Loss of endothelial PRDM16 did not alter RVSP or RVH (Fig. 2A,B). Pulmonary vascular remodeling was also not affected by endothelial PRDM16 deficiency. These findings suggest that, in contrast to the systemic circulation, PRDM16 may play a role in a non-endothelial compartment during P(A)H, e.g. in arterial smooth muscle cells or epithelial cells where it is also prominently expressed. To further investigate the involvement of PRDM16 in PAH, we will initially resort to mice and rats with a ubiquitous heterozygous deficiency for PRDM16, the latter of which we have successfully generated by CRISPR/Cas9 technology.

In conclusion, loss of endothelial PRDM16 does not accelerate or exacerbate hypoxia-induced PH.Figure 1For image description, please refer to the figure legend and surrounding text.  Figure 2For image description, please refer to the figure legend and surrounding text.