IGF1 Receptor Regulates Upward Firing Rate Homeostasis via the Mitochondrial Calcium Uniporter

Regulation of firing rate homeostasis constitutes a fundamental property of central neural circuits. While intracellular Ca2+ has long been hypothesized to be a feedback control signal, the molecular machinery enabling network-wide homeostatic response remains largely unknown. Here we show that deletion of insulin-like growth factor-1 receptor (IGF1R), a well-known regulator of neurodevelopment and ageing, limits firing rate homeostasis in response to inactivity, without altering the baseline firing rate distribution. Disruption of both synaptic and intrinsic homeostatic plasticity contributed to deficient firing rate homeostatic response. At the cellular level, a fraction of IGF1Rs was localized in mitochondria with the mitochondrial calcium uniporter complex (MCUc). IGF1R deletion suppressed mitochondrial Ca2+ (mitoCa2+) evoked by spike bursts by weakening mitochondria-to-cytosol Ca2+ coupling. This coupling was homeostatically maintained following inactivity in control, but upregulated in IGF1R-deficient neurons. MCUc overexpression in IGF1R-deficient neurons rescued the deficits in spike-to-mitoCa2+ coupling and firing rate homeostasis. Our findings highlight IGF1R as a key regulator of the integrated homeostatic response by tuning mitochondrial temporal filtering. Decline in mitochondrial reliability for burst transfer may drive dysregulation of firing rate homeostasis in brain disorders associated with abnormal IGF1R / MCUc signaling.