(T1151) INFLAMMATORY CYTOKINES TRIGGER THE ACTIVATION OF THE KYNURENINE PATHWAY OF TRYPTOPHAN METABOLISM: EFFECTS ON EMBRYONIC MOUSE NEURAL STEM CELL PROLIFERATION, HEALTH AND NAD STATE

Abstract: Neural stem cell (NSC) proliferation regulators underpin future cell therapies, while understanding NSC vulnerabilities during disease states could explain why innate repair in neurodegenerative/inflammatory diseases fails. The kynurenine pathway (KP) regulates essential amino acid tryptophan (TRP)’s bioavailability, notably induced by stimuli including interferons – components of a cell’s antiviral defences. In neurodegenerative diseases the KP is dysregulated, producing high levels of metabolites like potent neurotoxin Quinolinic acid (QUIN). QUIN metabolism by enzyme quinolinate phosphoribosyltransferase (QPRT) into cofactor NAD is rate-limited. We characterized KP/NAD genes via PCR, and hypothesized KP modulation by interferons alters embryonic mouse neural stem cell (emNSC) proliferation, neurosphere size and cell health (Muse flow cytometry assays).
We found Tryptophan-2,3-dioxygenase (TDO2) is a key regulator of initial TRP catabolism, having substantial basal expression (65.4527.45 (*1000 versus beta-actin) while modestly upregulated by interferons (type II family member IFN-gamma->2.7-fold)/type I IFN-beta->2.1-fold). IFN-gamma slightly upregulates alloenzyme indoleamine-2,3-dioxygenase (IDO1, 4.1+/-0.38); while IFN-beta has no effect. emNSCs varyingly express all KP genes basally including QPRT; upregulated by both IFNs. While IFN-gamma significantly increased neurosphere size (10IU/mL, 287.3+/-32.73um; p=0.0032; 100IU/mL, 305.7+/-10.64um; p=0.0005) versus controls (180.5+/-42.1um), it increased oxidative stress/caspase-activation, compromising cell health. Conversely, 50nM KYNA significantly grew neurosphere size (307.5+/-11.45um; p=0.0004) and retained cell health. Strikingly, both IDO-1/TDO2 are linked with NAD state, as siRNA with IFN-gamma gave increased NAD+/NADH ratio, typical of an active metabolic state.
In conclusion, we did the first KP/NAD gene expression screen. emNSCs are vulnerable to deleterious effects of interferons like IFN-gamma, which preferentially reduces (while IFN-beta enhances) enzymes linked with producing protective metabolites KYNA/Picolinic acid. Selective KP inhibition, or increasing KYNA could minimize cell death, improve regeneration, and optimize NSC proliferation therapeutically.

Funding Source: We acknowledge funding of the Peter Duncan Neurosciences Unit.

Clinical Trial ID number: