Significance of DNA base excision repair in the maintenance of mitochondrial function in Saccharomyces cerevisiae /

Mitochondria have an important role in cell metabolism, being the major site of ATP production via oxidative phosphorylation (OXPHOS). Accumulation of mtDNA mutations have been linked to the development of respiratory dysfunction, apoptosis, and aging. Base excision repair (BER) is the major and the only certain repair pathway existing in mitochondria that is in responsible for removing and repairing various base modifications as well as abasic sites (AP sites). In this research, Saccharomyces cerevisiae (S. cerevisiae) BER gene knockout strains, including 3 single DNA glycosylase gene knockout strains and Ap endonuclease (Apn 1 p) knockout strain were used to examine the importance of this DNA repair pathway to the maintenance of respiratory function. Here, I show that individual DNA glycosylases are nonessential in maintenance of normal function in yeast mitochondria, corroborating with previous research in mammalian experimental models. The yeast strain lacking Apn 1 p activity exhibits respiratory deficits, including inefficient and significantly low intracellular ATP level, which maybe due to partial uncoupling of OXPHOS. Growth of this yeast strain on respiratory medium is inhibited, but no evidence was found for increased ROS level in Apn 1 p mitochondria. This strain also shows an increased cell size, and this observation combined with an uncoupled OXPHOS may indicate a premature aging in the Apnlp knockout strain, but more evidence is needed to support this hypothesis. However, the BER is necessary for maintenance of mitochondrial function in respiring S.cerevisiae.

Intracellular antioxidant and DNA repair enzymes as correlates of stress resistance and longevity in vertebrates

In animals, both stress resistance and longevity appear to be influenced by the insulin/insulin-like growth factor-l signaling (lIS) pathway, the basic organization of which is highly conserved from invertebrates to vertebrates. Reduced lIS or genetic disruption of the lIS pathway leads to the activation of forkhead box transcription factors, which is thought to upregulate the expression of genes involved in enhancing stress resistance, including perhaps key antioxidant enzymes as well as DNA repair enzymes. Enhanced antioxidant and DNA repair capacities may underlie the enhanced cellular stress resistance observed in long-lived animals, however little data is available that directly supports this idea. I used three. experimental approaches to test the association of intracellular antioxidant and DNA base excision repair (BER) capacities with stress resistance and longevity: (1) a comparison of multiple vertebrate endotherm species of varying body masses and longevities; (2) a comparison of long-lived Snell dwarf mice and their normallittermates; and (3) a comparison of hypometabolic animals undergoing hibernation or estivation with their active counterparts. The activities of the five major intracellular antioxidant enzymes as well as the two rate-limiting enzymes in the BER pathway, apurininc/apyrimidinic (AP) endonuclease and polymerase ~, were measured. These measurements were performed in one or more of the following: (1) cultured dermal fibroblasts; (2) brain tissue; (3) heart tissue; (4) liver tissue. My results indicate that antioxidant enzymes are not universally upregulated in association with enhanced stress resistance and longevity. I also did not find that BER enzyme activity was positively correlated with longevity, in an inter-species context, though there was evidence for enhanced BER in long-lived Snell dwarf mice. Thus, while there were instances in which enhanced antioxidant and BER enzyme activities were associated with increased stress resistance and/or longevity, this was not universally the case, indicating that other mechanisms must be involved. These results suggest the need to re-examine existing 'oxidative stress' hypotheses of longevity and probe further into the molecular physiology of longevity to discover its mechanistic basis.

Letter written by Napoleon Buonaparte (Bonaparte) to Guillaume Thomas Francois Raynal, June 24, 1790

Translation: Sir, It will probably be difficult for you to remember among the many strangers who annoy you with their admiration of a person to whom you kindly made civilities last year1 during a pleasant conversation about Corsica. I would be grateful if you could take a look at this sketch of his history.2 I present here the first of two letters. If you agree to them, I will send you the end. My brother, whom I recommend not to forget his deputies' commission to escort Paoli to his country,3 and to come and receive a lesson in virtue and humanity, will give them to you. I respectfully your most humble and obedient servant.4 Buonaparte, artillery officer Ajaccio, [Corsica] June 24 the first year of freedom [1790]5 1 Relations between Napoleon and Raynal have begun in 1789, which seems to confirm a confidence to Las Cases ( Memorial of St. Helena , La Pléiade , vol. I, p. 83) . 2 Latest version of history project of Corsica : Letters on Corsica to Abbe Raynal . 3 Joseph is part of a delegation sent by the city of Ajaccio to host Paoli 's return from exile in London . In doing so he has to go through Marseille where Raynal resides. 4 Shipping autograph, National Archives , 400 AP Biography 1. In the first years of Napoleon Bonaparte (1840) , Coston gives a rough version of this letter that it dates from 1786 , which is impossible because Raynal did not return to France that ' in 1787. Published for the first time in the Memories of Lord Holland (1851) , shipping is now kept in the national Archives Napoleons funds . 5 The letter is dated "June 24, the first year of freedom" (the word "freedom" is underlined twice). Given the dates of stay in Corsica Napoleon, it seems that is present in Ajaccio the month of June in 1790.