Attenuated hypoxic pulmonary hypertension in mice lacking the 5-hydroxytryptamine transporter gene - PubMed (original) (raw)

Attenuated hypoxic pulmonary hypertension in mice lacking the 5-hydroxytryptamine transporter gene

S Eddahibi et al. J Clin Invest. 2000 Jun.

Abstract

Hypoxia is a well-recognized stimulus for pulmonary blood vessel remodeling and pulmonary hypertension development. One mechanism that may account for these effects is the direct action of hypoxia on the expression of specific genes involved in vascular smooth muscle cell (SMC) proliferation. Previous studies demonstrated that the serotonin (5-hydroxytryptamine; 5-HT) transporter (5-HTT) mediates the mitogenic activity of 5-HT in pulmonary vascular SMCs and is overexpressed during hypoxia. Thus, 5-HT-related mitogenic activity is increased during hypoxia. Here, we report that mice deficient for 5-HTT (5-HTT(-/-)) developed less hypoxic pulmonary hypertension and vascular remodeling than paired 5-HTT(+/+) controls. When maintained under normoxia, 5-HTT(-/-)-mutant mice had normal hemodynamic parameters, low blood 5-HT levels, deficient platelet 5-HT uptake, and unchanged blood levels of 5-hydroxyindoleacetic acid, a metabolite of 5-HT. After exposure to 10% O(2) for 2 or 5 weeks, the number and medial wall thickness of muscular pulmonary vessels were reduced in hypoxic 5-HTT(-/-) mice as compared with wild-type paired controls. Concomitantly, right ventricular systolic pressure was lower and right ventricle hypertrophy less marked in the mutant mice. This occurred despite potentiation of acute hypoxic pulmonary vasoconstriction in the 5-HTT(-/-) mice. These data further support a key role of 5-HTT in hypoxia-induced pulmonary vascular SMC proliferation and pulmonary hypertension.

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Figures

Figure 1

Figure 1

Individual and mean (horizontal line) values of platelet [3H]5-HT uptake (a) and whole blood concentrations of 5-HT (b) and 5-HIAA (c) in normoxic 5-HTT+/+ and _5-HTT_–/– mutant mice. NS, nonspecific uptake in the presence of 10 μM fluoxetine.

Figure 2

Figure 2

Individual and mean (horizontal line) values of RVSP in normoxic 5-HTT+/+ and _5-HTT_–/– mice under ventilation with room air (normoxia) and after 5 minutes of ventilation with a hypoxic gas mixture (hypoxia). Baseline RVSP under normoxic ventilation did not differ between 5-HTT+/+ and _5-HTT_–/– mice. The RVSP increase during acute hypoxia was significantly larger in _5-HTT_–/– than in 5-HTT+/+ mice (P < 0.01).

Figure 3

Figure 3

RVSP (a) and right ventricle/left ventricle plus septum weight (RV/LV+S) (b) in 5-HTT+/+ and 5-HTT_–/– mutant mice exposed to normoxia (N) (n = 9 in each genotype) or 10% O2 for 2 weeks (H-2 weeks) (n = 9 of each genotype) or 5 weeks (H-5 weeks) (n = 8 of each genotype). A_P < 0.05, B_P_ < 0.01, and C_P_ < 0.001 as compared with corresponding values in 5-HTT+/+ mice under similar conditions.

Figure 4

Figure 4

Distribution of vessels according to the accompanying airway. Fifty to 60 intraacinar vessels were analysed in each lung from mice of each genotype after exposure to hypoxia for 2 weeks (n = 9 of each genotype) or 5 weeks (n = 8 of each genotype). Percentages of nonmuscular (NM), partially muscular (PM), or fully muscular (M) vessels determined separately at the alveolar duct and alveolar wall levels differed significantly between 5-HTT+/+ and _5-HTT_–/– mice after exposure to hypoxia for either 2 weeks (P < 0.01) or 5 weeks (P < 0.001).

Figure 5

Figure 5

Normalized wall thickness measured in fully muscular arteries in lungs from 5-HTT+/+ and 5-HTT_–/– mice exposed to chronic hypoxia over 2 weeks (n = 9 mice of each genotype) or 5 weeks (n = 8 mice of each genotype). A_P < 0.05, B_P_ < 0.01 as compared with values in 5-HTT+/+ mice exposed to hypoxia of the same duration.

Figure 6

Figure 6

Western blot of 5-HTT protein in lungs from 5-HTT+/+ and _5-HTT_–/– mutant mice at the end of a 2-week exposure to normoxia or hypoxia. (a) The 5-HTT immunoreactivity in lungs from 5-HTT+/+ mice (lanes 1, 3) and _5-HTT_–/– mice (lanes 2, 4). The specific antibodies recognized a protein with an apparent molecular weight of 64 kDa. (b) Quantitation of the 5-HTT signal in lungs from normoxic and chronically hypoxic 5-HTT+/+ and 5-HTT_–/– mice (n = 5 in each group). A_P < 0.05 as compared with 5-HTT levels in normoxic 5-HTT+/+ mice.

Figure 7

Figure 7

Immunohistochemical localization of 5-HTT in distal pulmonary vessels from a 5-HTT+/+ mouse (a) and a _5-HTT_–/– mutant mouse (b) exposed to hypoxia for 2 weeks. In the pulmonary vessels from wild-type mice, dense immunostaining is visible in the smooth muscle cells. In contrast, only a very low level of background staining is observed in vessels from _5-HTT_–/– mice. Scale bar, 25 μm.

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