Age-related expression of prominent regulatory elements in mouse brain: catastrophic decline of FOXO3a

Abstract

Aging is associated with changes in regulation, particularly among diverse regulators in the brain. We assayed prominent regulatory elements in mouse brain to explore their relationship to one another, stress, and aging. Notably, unphosphorylated (activated) forkhead transcription factor 3a (uFOXO3a) expressed exponential decline congruent with increasing age-related mortality. Decline in uFOXO3a would impact homeostasis, aging rate, stress resistance, and mortality. We also examined other regulators associated with aging and FOXO3a: protein kinase B (PKB), the mechanistic target of rapamycin (mTOR), 70 kDa ribosomal S6 kinase (P70S6K), and 5' AMP-activated protein kinase (AMPK). It would require powerful regulatory distortion, conflicting tradeoffs and/or significant damage to inflict exponential decline of a transcription factor as crucial as FOXO3a. No other regulator examined expressed an exponential pattern congruent with aging. PKB was strongly associated with decreases in uFOXO3a, but the aging pattern of PKB did not support a causal linkage. Although mTOR expressed a trend for age-related increase, this was not significant. We considered that the mTOR downstream element, P70S6K, might suppress FOXO3a, but remarkably, it expressed a strong positive association. The age-related pattern of AMPK was also incompatible. Literature suggested the immunological regulator NFĸB (nuclear factor kappa-light-chain-enhancer of activated B cells) increases with age and suppresses FOXO3a. This would inhibit apoptosis, autophagy, mitophagy, proteostasis, detoxification, antioxidants, chaperones, and DNA repair, thus exacerbating aging. We conclude that a key aspect of aging involves distortion of key regulators in the brain.

Keywords: Aging; Error catastrophes; FOXO3a; Immunity; Inflammation; NFκB; PI3K-PKB; Stress resistance.

Fig. 1

Levels of unphosphorylated uFOXO3a (the active form) declined exponentially with age in normal untreated mice (p = 0.03147, r² = 0.07605, d.f. = 1,59)

Fig. 2

Ratio of Log(uFOXO/pFOXO) with age (r² = 0.101096, p = 0.01252, d.f. = 1,59)

Fig. 3

Phosphorylated pPKB impacts on unphosphorylated uFOXO (r² = 0.1211, p = 0.006914)

Fig. 4

pPKB had a somewhat parabolic pattern with age (p = 0.6973, d.f., 1,59)

Fig. 5

pPKB activity was closely associated with activation of pP70S6K (p = 0.000126, d.f. = 1,59, r² = 0.22216)

Fig. 6

Phosphorylated mTOR showed a modest trend for age-related increase, but this was not statistically resolved (linear regression, p < 0.5109)

Fig. 7

The pattern of pAMPK with age was somewhat parabolic (p = 0.52798, r² = 0.00678, d.f., 1,59)

Fig. 8

Activated uFOXO expressed a somewhat parabolic fit with activated pAMPK. Activity of uFOXO was higher at pAMPK levels of 0.1 to 0.2, but this was followed by lower responsiveness at higher levels of pAMPK (p = 0.881552, r² = 0.000392, d.f., 1,58)

Fig. 9

P70S6K surprisingly showed a strong positive association with uFOXO. This was most significant with a log-log transform (r² = 0.1218967, p = 0.00625, d.f. 1,58)