TNFα decreases mitochondrial movement in human airway smooth muscle

In airway smooth muscle (ASM) cells, excitation-contraction coupling is accomplished via a cascade of events that connect an elevation of cytosolic Ca 2+ concentration ([Ca 2+ ] cyt ) with cross-bridge attachment and ATP-consuming mechanical work. Excitation-energy coupling is mediated by linkage of the elevation of [Ca 2+ ] cyt to an increase in mitochondrial Ca 2+ concentration, which in turn stimulates ATP production. Proximity of mitochondria to the sarcoplasmic reticulum (SR) and plasma membrane is thought to be an important mechanism to facilitate mitochondrial Ca 2+ uptake. In this regard, mitochondrial movement in ASM cells may be key in establishing proximity. Mitochondria also move where ATP or Ca 2+ buffering is needed. Mitochondrial movement is mediated through interactions with the Miro-Milton molecular complex, which couples mitochondria to kinesin motors at microtubules. We examined mitochondrial movement in human ASM cells and hypothesized that, at basal [Ca 2+ ] cyt levels, mitochondrial movement is necessary to establish proximity of mitochondria to the SR and that, during the transient increase in [Ca 2+ ] cyt induced by agonist stimulation, mitochondrial movement is reduced, thereby promoting transient mitochondrial Ca 2+ uptake. We further hypothesized that airway inflammation disrupts basal mitochondrial movement via a reduction in Miro and Milton expression, thereby disrupting the ability of mitochondria to establish proximity to the SR and, thus, reducing transient mitochondrial Ca 2+ uptake during agonist activation. The reduced proximity of mitochondria to the SR may affect establishment of transient “hot spots” of higher [Ca 2+ ] cyt at the sites of SR Ca 2+ release that are necessary for mitochondrial Ca 2+ uptake via the mitochondrial Ca 2+ uniporter.