Browsing by Author "Slutsky, Inna"

The insulin-like growth factor-1 receptor (IGF-1R) signaling is a key regulator of lifespan, growth, and development. While reduced IGF-1R signaling delays aging and Alzheimer's disease progression, whether and how it regulates information processing at central synapses remains elusive. Here, we show that presynaptic IGF-1Rs are basally active, regulating synaptic vesicle release and short-term plasticity in excitatory hippocampal neurons. Acute IGF-1R blockade or transient knockdown suppresses spike-evoked synaptic transmission and presynaptic cytosolic Ca2+ transients, while promoting spontaneous transmission and resting Ca2+ level. This dual effect on transmitter release is mediated by mitochondria that attenuate Ca2+ buffering in the absence of spikes and decrease ATP production during spiking activity. We conclude that the mitochondria, activated by IGF-1R signaling, constitute a critical regulator of information processing in hippocampal neurons by maintaining evoked-to-spontaneous transmission ratio, while constraining synaptic facilitation at high frequencies. Excessive IGF-1R tone may contribute to hippocampal hyperactivity associated with Alzheimer's disease.

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 a network-wide homeostatic response remains largely unknown. We show that deletion of insulin-like growth factor-1 receptor (IGF-1R) limits firing rate homeostasis in response to inactivity, without altering the distribution of baseline firing rates. The deficient firing rate homeostatic response was due to disruption of both postsynaptic and intrinsic plasticity. At the cellular level, we detected a fraction of IGF-1Rs in mitochondria, colocalized with the mitochondrial calcium uniporter complex (MCUc). IGF-1R deletion suppressed transcription of the MCUc members and burst-evoked mitochondrial Ca2+ (mitoCa2+) by weakening mitochondria-to-cytosol Ca2+ coupling. Overexpression of either mitochondria-targeted IGF-1R or MCUc in IGF-1R–deficient neurons was sufficient to rescue the deficits in burst-to-mitoCa2+ coupling and firing rate homeostasis. Our findings indicate that mitochondrial IGF-1R is a key regulator of the integrated homeostatic response by tuning the reliability of burst transfer by MCUc. Based on these results, we propose that MCUc acts as a homeostatic Ca2+ sensor. Faulty activation of MCUc may drive dysregulation of firing rate homeostasis in aging and in brain disorders associated with aberrant IGF-1R/MCUc signaling.

Accumulated genetic evidence suggests that attenuation of the ratio between cerebral amyloid-beta A beta 40 and A beta 42 isoforms is central to familial Alzheimer's disease (FAD) pathogenesis. However, FAD mutations account for only 1-2% of Alzheimer's disease cases, leaving the experience-dependent mechanisms regulating A beta 40/42 an enigma. Here we explored regulation of A beta 40/42 ratio by temporal spiking patterns in the rodent hippocampus. Spike bursts boosted A beta 40/42 through a conformational change in presenilin1 (PS1), the catalytic subunit of gamma-secretase, and subsequent increase in A beta 40 production. Conversely, single spikes did not alter basal PS1 conformation and A beta 40/42. Burst-induced PS1 conformational shift was mediated by means of Ca2+-dependent synaptic vesicle exocytosis. Presynaptic inhibition in vitro and visual deprivation in vivo augmented synaptic and A beta 40/42 facilitation by bursts in the hippocampus. Thus, burst probability and transfer properties of synapses represent fundamental features regulating A beta 40/42 by experience and may contribute to the initiation of the common, sporadic Alzheimer's disease.