Serotonin 2A receptor inhibition protects against the development of pulmonary hypertension and pulmonary vascular remodeling in neonatal mice

Abstract

Pulmonary hypertension (PH) complicating bronchopulmonary dysplasia (BPD) worsens clinical outcomes in former preterm infants. Increased serotonin (5-hydroxytryptamine, 5-HT) signaling plays a prominent role in PH pathogenesis and progression in adults. We hypothesized that increased 5-HT signaling contributes to the pathogenesis of neonatal PH, complicating BPD and neonatal lung injury. Thus, we investigated 5-HT signaling in neonatal mice exposed to bleomycin, previously demonstrated to induce PH and alveolar simplification. Newborn wild-type mice received intraperitoneal PBS, ketanserin (1 mg/kg), bleomycin (3 U/kg) or bleomycin (3 U/kg) plus ketanserin (1 mg/kg) three times weekly for 3 wk. Following treatment with bleomycin, pulmonary expression of the rate-limiting enzyme of 5-HT synthesis, tryptophan hydroxylase-1 (Tph1), was significantly increased. Bleomycin did not affect pulmonary 5-HT 2A receptor (R) expression, but did increase pulmonary gene expression of the 5-HT 2BR and serotonin transporter. Treatment with ketanserin attenuated bleomycin-induced PH (increased RVSP and RVH) and pulmonary vascular remodeling (decreased vessel density and increased muscularization of small vessels). In addition, we found that treatment with ketanserin activated pulmonary MAPK and Akt signaling in mice exposed to bleomycin. We conclude that 5-HT signaling is increased in a murine model of neonatal PH and pharmacological inhibition of the 5-HT 2AR protects against the development of PH in neonatal lung injury. We speculate this occurs through restoration of MAPK signaling and increased Akt signaling.

Deletion of murine slc29a4 modifies vascular responses to adenosine and 5‐hydroxytryptamine in a sexually dimorphic manner

“…This may underlie the increased vasoconstriction seen with 5‐HT in the mesenteric arteries from the ENT4‐KO mice. A similar enhancement in 5‐HT constrictor activity is seen in pathological conditions (e.g., diabetes, pulmonary hypertension) that result in vascular damage (Delaney et al, 2018; MacLean, 2018; Watts & Davis, 2011). With respect to other genes examined, it was the male ENT4‐KO mice that showed the most extensive changes (relative to male WT), and mostly in those genes related to adenosine metabolism (i.e., increased ADK, ADA, ENT1, ENT2, and CNT2).…”

Platelet activation in experimental murine neonatal pulmonary hypertension

“…We previously reported that pharmacologic blockade of the 5‐HT 2A R prevents bleomycin‐induced PH and pulmonary vascular remodeling (Delaney et al, 2018). As platelets contain 99% of circulating 5‐HT, which is released upon activation, we tested the hypothesis that circulating platelets are activated and increased in the lungs of neonatal mice with bleomycin‐induced PH.…”

“…Beginning on days 1-2 of life, C57BL/6 wild-type mice (Jackson Laboratory) were injected with intraperitoneal phosphate-buffered saline (PBS) or bleomycin (3 units/kg, dissolved in PBS) (Hospira) three times per week for 3 weeks (total nine injections, 10 μl). This murine injury model of PH and BPD produces similar major pathologic findings to infants with PH and BPD including; impaired alveolar development (decreased radial alveolar counts, increased mean linear intercept and increased air space area), vascular remodeling (decreased vessel density, muscularization of small vessels, medial wall thickening), and PH (right ventricular hypertrophy and elevated right ventricular systolic pressure Delaney et al, 2018;Delaney et al, 2015;Sherlock et al, 2018). Bleomycin doses were adjusted for body weight at each injection.…”

“…Pulmonary hypertension (PH) is a life‐threatening condition that develops in 14%–25% of preterm infants with the lung disease of prematurity known as bronchopulmonary dysplasia (BPD) (Bhat, Salas, Foster, Carlo, & Ambalavanan, 2012; Mourani et al, 2015). The pathophysiology of neonatal PH associated with BPD involves alterations in numerous signaling pathways, including the serotonin (5‐HT) pathway (Alvira, 2016; Bhatt et al, 2001; Delaney et al, 2018; Le Cras et al, 1999; Le Cras, Markham, Tuder, Voelkel, & Abman, 2002). We have previously shown that pharmacologic inhibition of 5‐HT signaling via the 5‐HT 2A receptor (5‐HT 2A R) increases pulmonary blood flow in fetal sheep with PH and protects against the development of murine bleomycin‐induced neonatal PH (Delaney et al, 2013, 2018).…”

“…The pathophysiology of neonatal PH associated with BPD involves alterations in numerous signaling pathways, including the serotonin (5‐HT) pathway (Alvira, 2016; Bhatt et al, 2001; Delaney et al, 2018; Le Cras et al, 1999; Le Cras, Markham, Tuder, Voelkel, & Abman, 2002). We have previously shown that pharmacologic inhibition of 5‐HT signaling via the 5‐HT 2A receptor (5‐HT 2A R) increases pulmonary blood flow in fetal sheep with PH and protects against the development of murine bleomycin‐induced neonatal PH (Delaney et al, 2013, 2018). The vast majority of peripheral 5‐HT (98%) is synthesized by enterochromaffin cells of the small intestine and taken up by platelets via the serotonin transporter (SERT) where it is stored within dense granules (Barter & Pearse, 1953).…”