Hypothesis

Chronic activation of IKKβ/NF-κB in the mediobasal hypothalamus locks neuroendocrine circuits into a rigid, over‑consolidated state by suppressing pulsatile GnRH release through a SIRT1‑dependent metabolic checkpoint. Restoring SIRT1 activity with intermittent fasting re‑engages GnRH pulsatility, reduces inflammatory tone, and re‑opens plasticity windows without altering neuronal numbers.

Mechanistic Rationale

IKKβ/NF-κB signaling elevates c‑Fos/c‑Jun and PKC activity, directly repressing the GnRH promoter and cutting transcription by roughly half【1】. This repression is reinforced when hypothalamic neurons shift toward glycolysis, a metabolic state that favors NF-κB acetylation and transcriptional potency. SIRT1, an NAD⁺‑dependent deacetylase, removes acetyl groups from the NF‑κB p65 subunit, diminishing its DNA‑binding affinity and promoting a return to oxidative metabolism. In aging, declining NAD⁺ levels blunt SIRT1 activity, allowing NF‑κB to remain acetylated and transcriptionally active despite its canonical role in synaptic plasticity. Intermittent fasting raises circulating NAD⁺ and activates SIRT1, which then deacetylates NF‑κB, attenuates IKKβ‑driven c‑Fos/c‑Jun induction, and permits GnRH promoter accessibility. The resulting recovery of GnRH pulses reinstates downstream LH/FSH oscillations, stimulates hippocampal neurogenesis, and rescues LTP—a reversal of the over‑consolidated inflammatory lock.

Testable Predictions

1. Aged mice subjected to 16‑hour daily intermittent fasting for 8 weeks will show increased hypothalamic NAD⁺/NADH ratio, elevated SIRT1 activity, and reduced acetylated p65 NF‑κB levels compared with ad‑fed controls.
2. GnRH mRNA and pulsatile secretion in the median eminence will rise by ≥30 % in fasted aged mice, coinciding with a ≥25 % increase in LH pulse frequency.
3. Hippocampal slice LTP and spatial memory performance (Morris water maze) will improve to levels indistinguishable from young adult mice only when fasting is combined with intact SIRT1 (SIRT1‑conditional knockout in hypothalamus will abolish the benefit).
4. Microglial TNF‑α expression will drop proportionally to SIRT1 activation, and IKKβ pharmacological inhibition will not produce additive effects beyond fasting, indicating a shared pathway.

Experimental Design

• Subjects: 20‑month‑old C57BL/6J mice (n = 10 per group) and SIRT1‑hypothalamus‑KO littermates.
• Interventions: (a) ad libitum feeding, (b) intermittent fasting (24 h fasting/24 h refeeding cycles), (c) IKKβ inhibitor (SC‑514) administered via osmotic pump, (d) fasting + IKKβ inhibitor.
• Readouts: Hypothalamic NAD⁺/NADH ratio (enzymatic assay), SIRT1 activity (fluorometric deacetylase assay), acetylated p65 NF‑κB (Western blot), GnRH mRNA (qPCR), serial blood sampling for LH pulses (ELISA), hippocampal LTP (field electrophysiology), behavioral testing (novel object location, water maze), microglial TNF‑α (immunohistochemistry).
• Analysis: Two‑way ANOVA with factors diet and genotype; post‑hoc Tukey tests. Significance set at p < 0.05.

If fasting restores GnRH pulsatility and cognitive performance via SIRT1‑mediated NF‑κB deacetylation, the data will support the idea that age‑related rigidity is a metabolically gated, reversible over‑consolidation rather than irreversible neurodegeneration. Failure to observe these changes would falsify the hypothesis and suggest that alternative mechanisms sustain the inflammatory lock.