Nrf2 in Aging and Longevity

The transcription factor nrf2 regulates levels of antioxidant proteins, a part of the response to everyday cellular stress, such as that induced by raised mitochondrial activity and greater generation of reactive oxygen species (ROS) during exercise. Greater nrf2 activity shows up in long-lived species and in the modest slowing of aging that can be achieved via hormesis in some species. Here is an open access review paper on this topic:

The role of Nrf2 in responding to cytotoxic stressors is well defined. However, only within the last few years have studies elucidated how Nrf2 function changes with age and how changes in Nrf2 activity contribute to the aging phenotype. Aged mice show similar losses in cellular redox capacity to those observed in Nrf2 knockout mice, suggesting that Nrf2 dysregulation with age may be responsible for the loss of cellular redox status. Diminished Nrf2 target gene expression with age is accompanied by increased muscle ROS production, glutathione depletion, and increased oxidant damage to proteins, DNA, and lipids in both humans and rodents. Therefore, given that Nrf2 activity decreases with age alongside increased oxidant stress, interventions that activate Nrf2 may impact the aging process and longevity.

Support for the role of Nrf2 in regulation of lifespan comes from Nrf2 gain of function and loss of function studies. For example, experimental deletion of the antielectrophilic gene glutathione transferase (gGsta4) activated Nrf2 and significantly extended lifespan in mice. This mutation increased electrophilic lipid peroxidation products and increased nuclear Nrf2 activity by 43% and 38% in liver and skeletal muscle, respectively. The authors propose that deletion of this glutathione transferase gene resulted in chronic moderate Nrf2 activation and presumably elevated downstream Nrf2 signaling throughout the mouse lifespan. Studies of the Nrf2 homolog SKN-1 in Caenorhabditis elegans (C. elegans) further suggest that Nrf2 may be implicated in longevity processes. Upon activation, SKN-1 upregulates genes involved in the oxidative stress response, including many orthologs to those regulated by mammalian Nrf2. Similar to mouse Nrf2 knockouts, SKN-1 mutants show diminished resistance to oxidative stress and shortened lifespan. On the other hand, moderate overexpression of a constitutively active SKN-1 increases lifespan, alongside increased resistance to oxidative stress.

The naked mole rat is an exceptionally long-lived species, with a lifespan four times longer than similarly sized rodents, thus making the naked mole rat an important model for longevity studies. Naked mole rats do not have typical lifespan curves in which mortality rates increase with age, but rather they experience few of the biological changes typically associated with aging. Naked mole rats also have significantly elevated proteasome quality control mechanisms. The high breakdown and clearance of damaged proteins is suspected to be largely due to increased Nrf2 expression. In support of the hypothesized role of Nrf2 in naked mole rat longevity, under nonstressed conditions, naked mole rats have greater protein levels of Nrf2 and greater expression of Nrf2-regulated enzymes in fibroblasts and liver. These data suggest Nrf2 may be responsible for the heightened quality control mechanisms in naked mole rats and may be associated with their exceptional longevity.

Link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4637130/

Comments

Hi all !

Summary : Nrf2-mediated effect are Redox based via ARE/EpRE; thus Redox control is behind this.

For me Nrf2 is something good and bad, I read so many studies of how it is highly protective and great overall; and it is. But then, I just take in some Nrf2 activators and think, ok, this is not going to make me live that longer; healthier for a bit longer yes though (definitely a good thing)...some Nrf2 activators such as cinnamon, ginger and some other spices/herbs all act through the Nrf2 activation pathway. Nrf2-signaling activity has been shown to increase with MLSP (Maximum Lifespan Potential) of animals, but not the Nrf2-protein content. If these activators can't do anything on the MSLP of animals but rather help average healthy lifespan, yet Nrf2 activation equals to MLSP; then why ? Something doesn't gel. Either they are not strong enough or some other reason, it may take just way too much high levels (toxic) to really increase Nrf2 activity (since Nrf2 is a sort of hormesis effect from oxidation rise that *signals* an increase/preps up the oxidative stress defense mechanism that is ARE. Yet, in this study here, they mess around with the Redox, altering and litterally knocking-out Glutathione transferase (an extremely important element of the Redox), Nrf2 and the antioxidant/electrophile response element (ARE/EpRE) reception of signal from electrophilic stress, then signals very precise things to the Redox control of the cell; and if the Redox is altered by ARE/EpRE then the effects of the latter all due to the former (Redox shifts). It is not so much Nrf2-activity that is correlated to MLSP, it is the Redox balance that is (altered via Nrf2 ARE/EpRE) orchestrating this. How so ? Well, for example, Glutathione transferase and Glutathione Peroxidase enzymes have been shown to be elevated in states of diseases; meaning they are sort of a defense mechanism compensation feedback (meaning that inside, oxidation is rising and both GT and GP try to migitate that; but they are sort of vague markers that damage is going on and the body tries to mitigate it by activating them); this study ko's GTs and of course, lipid peroxidation rises and signals Nrf2 that activates the ARE/EpRE (*A*RE...Antioxidant Response Element...I mean when you think about it...it is activating Antioxidants (Enzymes and systems) to mitigate the rising damage from GTs KO; what is mostly ARE...it is activation of the GSH antioxidant creation system that is Cysteine Gamma-glutamyl Ubiquitin Ligase and Glutathione Synthetase (Glutathione Reductase is another one, but here GSH creation is needed to offset rising GSSG from GT ko). It's especially important to understand that the EpRE has cysteine residues in gene code that if removed EpRE/ARE becomes useless (so thus Nrf2 too, it's just upstream. The hormetic effect is lost) : Cysteine is necessary for Redox control and GSH formation (cysteine is one the 3 amino acids for glutathione tripeptide formation, with glutamate and glycine the others). Nrf2, by ARE/EpRE signal, also increases mitochondrial mnSOD/SOD2 (Manganese Super Oxidase Dismutase) and mitochondrial CAT (Catalase) among others. Without the artillery of Redox antioxidant enzymes activation credit, Nrf2/ARE/EpRE would be nothing; showing the Redox control between Oxidative state:Reduced state (the fluctation of negative (reduced) or positive mV cell state (oxidized)) the responsable downstream of this Nrf2 lifespan lengthening effect.

'' We found that constitutive Nrf2-signaling activity was positively correlated (P = 0.0285) with MLSP. ''

'' Antioxidant enzymes [via ARE/EpRE by Nrf2] maintain cellular redox homeostasis. Manganese superoxide dismutase (MnSOD), an enzyme located in mitochondria, is the key enzyme that protects the energy-generating mitochondria from oxidative damage. Levels of MnSOD are reduced in many diseases, including cancer, neurodegenerative diseases, and psoriasis. ''

'' Reduction potential [Re part of Redox] (also known as redox potential, oxidation / reduction potential, ... Reduction potential is measured in volts (V), or millivolts (mV). ''

1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4378420/
2. http://www.hindawi.com/journals/omcl/2015/732596/
3. http://www.hindawi.com/journals/er/2011/387176/
4. https://en.wikipedia.org/wiki/Reduction_potential

Posted by: CANanonymity at November 27th, 2015 9:41 AM

Extreme 10-fold Lifespan extension in C.elegans worms is mediated in part via Redox enzymatic defense mechanism SOD-3 (SOD-3 is mitochondrial worm version homologue of mitochondrial human manganese SOD-2, showing that complex I mtROS making mitochondrial DNA damage/lesions/deletions are the major cause of aging because of loss of ATP energy creation from damaged mitochondria/mtDNA. That is also why reduced lipid mitochondrial Peroxidation Index (PI) and double-bond index DBI reduces mitochondrial ROS and increases MLSP from better mtATP output).
The worms that live barely a month (20 days) are extended to nearly 3/4 of a year (180-250 day) MLSP lifespans via DAF-16/FOXO/SIRT activation/blocking of insulin signaling PIP3 kinase abrogation and SOD-3/PEPCK transcript/enzymes increase.

'' As a result of disrupted IIS [[insulin/IGF (insulin-like growth factor)-like signalling] inhibition of DAF-16/FOXO, two of its positive target genes, sod-3 (i) and pepck (j), are strongly induced in age-1(mg44) F2 worms [the 10-fold extended lifespan mutant worms]. ''
'' SOD-3 is an Fe++/Mn++ superoxide dismutase, believed to be mitochondrial ''
'' ... activity in age-1(mg44) adults: sod-3, encoding mitochondrial superoxide dismustase ''

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3610087/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885961/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661368/
http://www.ncbi.nlm.nih.gov/pubmed/20354111
http://www.ncbi.nlm.nih.gov/pubmed/19764929

Posted by: CANanonymity at November 27th, 2015 10:50 AM

Here Reis and Hulbert show that PI lipid modulation in mitochondrial membranes phospholipids is a cause of MLSP increase in C.elegans, the lipid peroxidation resistance also thus alters Redox systems such as SOD-3 in the mitochondria; thus the mitochondrial DNA lesions and deletions during lipid peroxidation formation (8-oxo-dG formation) = MLSP. It is important to understand this is a Decrease of lipid peroxidation in lower PI, while Glutathione Transferase KO Nrf2 activation is an Increase of lipid peroxidation - both act on the Redox systems; showing wether high (hormesis activation) or low peroxidation (prevention/avoiding damage); the end result is the same - both are 'signals' to the Redox.

1. http://www.impactaging.com/papers/v3/n2/full/100275.html
2. http://www.impactaging.com/papers/v3/n2/full/100288.html

Posted by: CANanonymity at November 27th, 2015 11:00 AM

''gamma-Glutamyl transpeptidase is induced by 4-hydroxynonenal via EpRE/Nrf2 signaling in rat epithelial type II cells.''

4-hydroxynonenal (4-HNE) perodixation causes the Redox to shift and respond by gamma-glutamyl transpeptidase activity increase in feedback compensation against 4-HNE peroxidation damage.

''Coffee constituents [rapamycin/mTOR/SIR/Foxo modulator mimetic] as modulators of Nrf2 nuclear translocation and ARE (EpRE)-*dependent* gene expression.''

Coffee/rapamycin/spices herbs/Calorie restriction alter EpRE/ARE via Nrf2 nuclear translocation (in nucleus).

3. http://www.ncbi.nlm.nih.gov/pubmed/16631518
4. http://www.ncbi.nlm.nih.gov/pubmed/20655719

Posted by: CANanonymity at November 27th, 2015 12:17 PM

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