Hypothesis

We propose that hypothalamic IKKβ/NF-κB activation directly programs NAD+ decline by transcriptionally repressing the salvage enzyme Nampt and inducing the NAD+-consuming enzyme CD38 in GnRH‑producing neurons and neighboring glia. This creates a neuroendocrine‑metabolic axis whereby inflammatory signaling reduces cellular NAD+ pools, impairing SIRT1‑dependent deacetylation of clock and metabolic genes, thereby accelerating systemic aging.

Mechanistic Basis

• NF-κB p65 binds to promoter regions of Nampt, recruiting HDACs and lowering mRNA stability, as shown in macrophage models (see 1).
• Simultaneously, NF-κB drives Cd38 expression via upstream STAT1 activation, a pathway observed in astrocytes during chronic inflammation (2).
• In the mediobasal hypothalamus, microglia‑derived TNF‑α activates neuronal IKKβ/NF-κB, establishing a feed‑forward loop that sustains low Nampt and high CD38 activity.
• Reduced NAD+ limits SIRT1 activity, leading to hyperacetylation of PGC‑1α and BMAL1, dampening mitochondrial output and circadian robustness.
• The resulting neuroendocrine deficit manifests as diminished GnRH pulse frequency, lower LH/FSH secretion, and downstream gonadal atrophy, mirroring the phenotype of MBH‑IKKβ overexpression.

Testable Predictions

1. Conditional IKKβ activation in hypothalamic GnRH neurons will decrease Nampt mRNA and protein while increasing CD38, measurable by qPCR and Western blot within 48 h.
2. Pharmacological blockade of CD38 (using 78c) or supplementation with NMN will rescue NAD+ levels and restore GnRH release in IKKβ‑overexpressing mice, even without altering NF‑κB activity.
3. Microglia‑specific IKKβ knockout will prevent NF‑κB‑mediated Nampt suppression and extend lifespan, an effect abrogated by neuron‑restricted CD38 overexpression.
4. Single‑cell RNA‑seq of the mediobasal hypothalamus from aged mice will reveal a clonal subset of GnRH neurons with concurrent high RelA (p65) nuclear signal, low Nampt, and high CD38 transcripts.

Experimental Approach

• Generate GnRH‑Cre;Ikkβ^fl/fl mice for neuron‑specific IKKβ deletion and complementary GnRH‑Cre;Ikkβ^CA (constitutively active) lines for gain‑of‑function.
• Measure hypothalamic NAD+ by LC‑MS/MS, Nampt and CD38 expression by immunofluorescence and RNAscope.
• Assess GnRH pulsatility via microdialysis and LH serum titers.
• Treat cohorts with NMN (400 mg/kg/day) or CD38 inhibitor (78c, 5 mg/kg) and monitor survival, frailty index, and metabolic phenotypes.
• Perform ATAC‑seq on sorted GnRH neurons to identify NF‑κB‑dependent chromatin changes at Nampt and CD38 loci.

If NF‑κB directly represses Nampt and induces CD38, then rescuing NAD+ downstream should uncouple inflammatory signaling from metabolic decay, demonstrating that NAD+ decline is an actively programmed output of the hypothalamic aging pacemaker rather than passive damage.