Enhanced axonal mitochondrial motility and neural activity-induced energy deficits destabilize synaptic transmission in models of bipolar disorder.

Synaptic communication requires mitochondria to supply ATP and buffer calcium at presynaptic terminals. In bipolar disorder, manic episodes are associated with elevated mood and neural activity, but the underlying cellular mechanisms remain unclear. Here we show that hiPSC-derived cortical neurons from donors with bipolar disorder exhibit increased axonal mitochondrial motility and frequent mitochondrial entry-exit transitions, reducing stable mitochondrial retention at presynaptic terminals. This destabilizes local ATP maintenance and calcium buffering, increasing synaptic variability without altering mean synaptic strength. Knockdown of the bipolar disorder risk gene AKAP11 in mouse neurons reproduced these synaptoenergetic deficits. HiPSC-derived neurons from donors with bipolar disorder exhibited reduced expression of the mitochondrial anchor protein syntaphilin(SNPH), and  snph knockout mice displayed manic-like behavioral phenotypes. Lithium restored presynaptic mitochondrial retention, improved ATP maintenance, rescued synaptic variability, and reversed behavioral phenotypes. These findings support impaired presynaptic mitochondrial retention and activity-induced synaptoenergetic deficits as cellular mechanisms contributing to bipolar disorder.