Primary role of mitochondrial Rieske iron-sulfur protein in hypoxic ROS production in pulmonary artery myocytes

Area of Science:

• Cell Biology
• Mitochondrial Function
• Cardiovascular Physiology

Background:

• Hypoxic pulmonary vasoconstriction (HPV) is a critical circulatory response.
• Mitochondria and reactive oxygen species (ROS) are implicated in HPV, but direct mechanisms remain unclear.

Purpose of the Study:

• To investigate if hypoxia directly impacts ROS production in pulmonary artery smooth muscle cell (PASMC) mitochondria.
• To determine if the Rieske iron-sulfur protein in mitochondrial complex III mediates hypoxic ROS production and subsequent HPV.

Main Methods:

• Isolated mitochondria and complex III from PASMCs were used to measure ROS production under hypoxia.
• siRNA was employed to silence Rieske iron-sulfur protein expression.
• ROS production was assessed using dichlorodihydrofluorescein/diacetate and the pHyPer biosensor.
• Intracellular calcium ([Ca(2+)](i)) and vasoconstriction in isolated pulmonary arteries (PAs) were measured.

Main Results:

• Hypoxia significantly increased ROS production in isolated PASMC mitochondria and cells.
• Hypoxic ROS generation was observed in isolated mitochondrial complex III.
• Rieske iron-sulfur protein silencing abolished hypoxia-induced ROS production, while overexpression enhanced it.
• Rieske iron-sulfur protein silencing inhibited hypoxia-induced increases in intracellular calcium and pulmonary vasoconstriction.

Conclusions:

• Mitochondria are direct targets of hypoxia in PASMCs.
• The Rieske iron-sulfur protein in mitochondrial complex III is a primary mediator of hypoxic ROS generation.
• This mechanism, involving ROS and increased intracellular calcium, leads to HPV.