Transcriptional changes which could be described as compensatory mechanisms to counteract the pulmonary hypertension include down-regulation of genes involved in TREM1 signaling (TREM1, TLR4, IL1B, and ITGAX) and up-regulation of NOS3. Pulmonary inflammatory responses play an important role in hypoxia-induced vascular remodeling [33] and down-regulation of TREM1 signaling could be a compensatory response to attenuate pulmonary inflammatory responses. Here, TLR4 is linked to pulmonary arterial hypertension.