Abstract
Understanding the biology of ageing in order to develop healthy ageing treatments is more important than ever as the general population ages. Oxidative stress is known for its potential to cause chronic disease by inducing molecular damage and has subsequently been linked to ageing. Recent studies have shown that many oxidants possess important signalling properties which suggests they have other functions besides inducing molecular damage. Slightly elevated levels of oxidants which is considered beneficial to an organism has been termed ‘oxidative eustress’. Many studies have linked longevity and healthy-ageing to oxidative eustress as stress defences are stimulated in a protective capacity
Peroxiredoxins (Prdxs) are an antioxidant family of ubiquitous, relatively small thiol peroxidases of ~20 kDa. Eukaryotic Prdxs use catalytic cysteine residues to regulate hydrogen peroxide (H2O2) signalling by catalysing disulfide bond formation in targets via a redox relay mechanism. Prdxs have been proposed to exist in a redox signalling network with other antioxidants thioredoxin, thioredoxin reductase, and NADPH from the pentose phosphate pathway. Alterations to Prdx activity and its associated antioxidant signalling network have subsequently been proposed as important components of ageing. While underlying mechanism(s) are unknown, Prdxs have been implicated in an adaptive stress response that is thought to prolong life. Similar increased longevity effects have also been observed in mice using metformin, rapamycin and 17-α-estradiol.
The aim of this project is to determine whether ‘healthy-ageing’ drugs that increase lifespan in mice alter the Prdx redox network in Jurkat cells. These proposed healthy-ageing drugs have been linked to the alteration of metabolic signalling pathways that affect NADPH production. NADPH is an essential component of the Prdx redox network which is required for sustained metabolism of H2O2 and subsequent redox signalling via Prdx. Therefore, healthy-ageing drugs may rely at least partly on modulation of NADPH production and associated Prdx redox signalling to mediate their longevity effects.
Differential expression analysis was used to investigate whether expression of Prdxs, Trxs, and TrxRs changed in response to treatment of metformin, rapamycin, 17-β-estradiol, or 17-α-estradiol. Prdx and Trx showed no significant changes in mRNA expression in response to metformin, rapamycin, 17-β-estradiol, or 17-α-estradiol treatment. Expression analysis of some datasets suggests that 17-α-estradiol and 17-β-estradiol may downregulate TrxR in some cell types but more analysis would be required in the future to confirm this. Time course experiments with 20 μM H2O2 treatment in the absence or presence of 17-β-estradiol, 17-α-estradiol, metformin, and rapamycin have also being undertaken to measure the response of cytosolic Prdx1, Prdx2 and mitochondrial Prdx3. Results show that neither 17-α-estradiol nor 17-β-estradiol alter the Prdx redox network response to H2O2 treatment. Metformin treatment appeared to inhibit the response of the Prdx redox network to H2O2 treatment whereas rapamycin treatment appeared to enhance it. These observations suggest that some of the healthy-ageing drugs investigated in this thesis may rely at least partly on modulation of Prdx activity for their effects on longevity.