Interleukin-6 trans-signaling contributes to chronic hypoxia-induced pulmonary hypertension

Interleukin-6 (IL-6) is a pleotropic cytokine that signals through the membrane-bound IL-6 receptor (mIL-6R) to induce antiinflammatory
(‘‘classic-signaling’’) responses. This cytokine also binds to the soluble IL-6R (sIL-6R) to promote inflammation
(‘‘trans-signaling’’). mIL-6R expression is restricted to hepatocytes and immune cells. Activated T cells release sIL-6R into adjacent
tissues to induce trans-signaling. These cellular actions require the ubiquitously expressed membrane receptor gp130. Reports
show that IL-6 is produced by pulmonary arterial smooth muscle cells (PASMCs) exposed to hypoxia in culture as well as the
medial layer of the pulmonary arteries in mice exposed to chronic hypoxia (CH), and IL-6 knockout mice are protected from CHinduced
pulmonary hypertension (PH). IL-6 has the potential to contribute to a broad array of downstream effects, such as cell
growth and migration. CH-induced PH is associated with increased proliferation and migration of PASMCs to previously nonmuscularized
vessels of the lung. We tested the hypothesis that IL-6 trans-signaling contributes to CH-induced PH and arterial
remodeling. Plasma levels of sgp130 were significantly decreased in mice exposed to CH (380 mmHg) for five days compared to
normoxic control mice (630 mmHg), while sIL-6R levels were unchanged. Consistent with our hypothesis, mice that received the
IL-6 trans-signaling-specific inhibitor sgp130Fc, a fusion protein of the soluble extracellular portion of gp130 with the constant
portion of the mouse IgG1 antibody, showed attenuation of CH-induced increases in right ventricular systolic pressure, right
ventricular and pulmonary arterial remodeling as compared to vehicle (saline)-treated control mice. In addition, PASMCs cultured
in the presence of IL-6 and sIL-6R showed enhanced migration but not proliferation compared to those treated with IL-6 or sIL-6R
alone or in the presence of sgp130Fc. These results indicate that IL-6 trans-signaling contributes to pulmonary arterial cell
migration and CH-induced PH.