Mitochondrial association of myocilin, product of a glaucoma gene, in human trabecular meshwork cells

The trabecular meshwork (TM), an ocular tissue next to the cornea, is a major site for regulation of the aqueous humor outflow. Malfunctioning of this tissue is believed to be responsible for development of glaucoma, a major blinding disease. Myocilin is a gene directly linked to the most common form of glaucoma. Its protein product has been localized to both intra- and extra-cellular sites in TM cells. This study was to investigate the association of myocilin with mitochondria in TM cells. In vitro mitochondrial import assays showed that myocilin was imported to the TM mitochondria, targeting to mitochondrial membranes and/or the intermembrane space. The targeting was mediated mostly via the amino-terminal region of myocilin. When myocilin expression was induced either by treatment with dexamethasone or transfection with a myocilin construct, the mitochondrial membrane potential in TM cells, as assessed by JC-I staining, was lowered. Subcellular fractionation and Western blot analyses confirmed that a portion of myocilin sedimented with the mitochondrial fractions. Upon anti-Fas treatment to provoke apoptosis, an increase of myocilin distribution in cytosolic fraction was observed, I suggesting that myocilin was partially released from mitochondrial compartments. These results confirmed the association of myocilin with TM cell mitochondria and indicated that myocilin may have a proapoptotic role in TM cells.