TPH1 and pulmonary arterial hypertension: Therefore, it is notable that Tph1(−/−) mice over-expressed genes related to hyaluronic acid synthesis and deposition: Has2 and Hapln3. Moreover, Retnla (resistin like alpha, HIMF, FIZZ1) was also up-regulated in Tph1(−/−) mice, and this gene has been implicated in the development of hypoxia-induced PAH [19], [26].