Serine metabolism contributes to cell survival by regulating extracellular pH and providing an energy source in Saccharomyces cerevisiae.

Changes in extracellular pH affect the homeostasis and survival of unicellular organisms. Supplementation of culture media with amino acids can extend the lifespan of budding yeast, Saccharomyces cerevisiae, by alleviating the decrease in pH. However, the optimal amino acids to use to achieve this end, and the underlying mechanisms involved, remain unclear. Here, we describe the specific role of serine metabolism in the regulation of pH in a medium. The addition of serine to synthetic minimal medium suppressed acidification, and at higher doses increased the pH. CHA1, which encodes a catabolic serine hydratase that degrades serine into ammonium and pyruvate, is essential for serine-mediated alleviation of acidification. Moreover, serine metabolism supports extra growth after glucose depletion. Therefore, medium supplementation with serine can play a prominent role in the batch culture of budding yeast, controlling extracellular pH through catabolism into ammonium and acting as an energy source after glucose exhaustion.

Gentirigeoside B from Gentiana rigescens Franch Prolongs Yeast Lifespan via Inhibition of TORC1/Sch9/Rim15/Msn Signaling Pathway and Modification of Oxidative Stress and Autophagy.

Gentirigeoside B (GTS B) is a dammaren-type triterpenoid glycoside isolated from G. rigescens Franch, a traditional Chinese medicinal plant. In the present study, the evaluation of the anti-aging effect and action mechanism analysis for this compound were conducted. GTS B significantly extended the replicative lifespan and chronological lifespan of yeast at doses of 1, 3 and 10 µM. Furthermore, the inhibition of Sch9 and activity increase of Rim15, Msn2 proteins which located downstream of TORC1 signaling pathway were observed after treatment with GTS B. Additionally, autophagy of yeast was increased. In addition, GTS B significantly improved survival rate of yeast under oxidative stress conditions as well as reduced the levels of ROS and MDA. It also increased the gene expression and enzymatic activities of key anti-oxidative enzymes such as Sod1, Sod2, Cat and Gpx. However, this molecule failed to extend the lifespan of yeast mutants such as ∆cat, ∆gpx, ∆sod1, ∆sod2, ∆skn7 and ∆uth1. These results suggested that GTS B exerts an anti-aging effect via inhibition of the TORC1/Sch9/Rim15/Msn signaling pathway and enhancement of autophagy. Therefore, GTS B may be a promising candidate molecule to develop leading compounds for the treatment of aging and age-related disorders.

Ehretiquinone from Onosma bracteatum Wall Exhibits Antiaging Effect on Yeasts and Mammals through Antioxidative Stress and Autophagy Induction.

The antiaging benzoquinone-type molecule ehretiquinone was isolated in a previous study as a leading compound from the herbal medicine Onosma bracteatum wall. This paper reports the antiaging effect and mechanism of ehretiquinone by using yeasts, mammal cells, and mice. Ehretiquinone extends not only the replicative lifespan but also the chronological lifespan of yeast and the yeast-like chronological lifespan of mammal cells. Moreover, ehretiquinone increases glutathione peroxidase, catalase, and superoxide dismutase activity and reduces reactive oxygen species and malondialdehyde (MDA) levels, contributing to the lifespan extension of the yeasts. Furthermore, ehretiquinone does not extend the replicative lifespan of Δsod1, Δsod2, Δuth1, Δskn7, Δgpx, Δcat, Δatg2, and Δatg32 mutants of yeast. Crucially, ehretiquinone induces autophagy in yeasts and mice, thereby providing significant evidence on the antiaging effects of the molecule in the mammalian level. Concomitantly, the silent information regulator 2 gene, which is known for its contributions in prolonging replicative lifespan, was confirmed to be involved in the chronological lifespan of yeasts and participates in the antiaging activity of ehretiquinone. These findings suggest that ehretiquinone shows an antiaging effect through antioxidative stress, autophagy, and histone deacetylase Sir2 regulation. Therefore, ehretiquinone is a promising molecule that could be developed as an antiaging drug or healthcare product.

Gentiopicroside, a Secoiridoid Glycoside from Gentiana rigescens Franch, Extends the Lifespan of Yeast via Inducing Mitophagy and Antioxidative Stress.

Gentiopicroside (GPS), an antiaging secoiridoid glycoside, was isolated from Gentiana rigescens Franch, a traditional Chinese medicine. It prolonged the replicative and chronological lifespans of yeast. Autophagy, especially mitophagy, and antioxidative stress were examined to clarify the mechanism of action of this compound. The free green fluorescent protein (GFP) signal from the cleavage of GFP-Atg8 and the colocation signal of MitoTracker Red CMXRos and GFP were increased upon the treatment of GPS. The free GFP in the cytoplasm and free GFP and ubiquitin of mitochondria were significantly increased at the protein levels in the GPS-treated group. GPS increased the expression of an essential autophagy gene, ATG32 gene, but failed to extend the replicative and chronological lifespans of ATG32 yeast mutants. GPS increased the survival rate of yeast under oxidative stress condition; enhanced the activities of catalase, superoxide dismutase, and glutathione peroxidase; and decreased the levels of reactive oxygen species and malondialdehyde. The replicative lifespans of Δsod1, Δsod2, Δuth1, and Δskn7 were not affected by GPS. These results indicated that autophagy, especially mitophagy, and antioxidative stress are involved in the antiaging effect of GPS.

Parishin from Gastrodia elata Extends the Lifespan of Yeast via Regulation of Sir2/Uth1/TOR Signaling Pathway.

Parishin is a phenolic glucoside isolated from Gastrodia elata, which is an important traditional Chinese medicine; this glucoside significantly extended the replicative lifespan of K6001 yeast at 3, 10, and 30 µM. To clarify its mechanism of action, assessment of oxidative stress resistance, superoxide dismutase (SOD) activity, malondialdehyde (MDA), and reactive oxygen species (ROS) assays, replicative lifespans of sod1, sod2, uth1, and skn7 yeast mutants, and real-time quantitative PCR (RT-PCR) analysis were conducted. The significant increase of cell survival rate in oxidative stress condition was observed in parishin-treated groups. Silent information regulator 2 (Sir2) gene expression and SOD activity were significantly increased after treating parishin in normal condition. Meanwhile, the levels of ROS and MDA in yeast were significantly decreased. The replicative lifespans of sod1, sod2, uth1, and skn7 mutants of K6001 yeast were not affected by parishin. We also found that parishin could decrease the gene expression of TORC1, ribosomal protein S26A (RPS26A), and ribosomal protein L9A (RPL9A) in the target of rapamycin (TOR) signaling pathway. Gene expression levels of RPS26A and RPL9A in uth1, as well as in uth1, sir2 double mutants, were significantly lower than those of the control group. Besides, TORC1 gene expression in uth1 mutant of K6001 yeast was inhibited significantly. These results suggested that parishin exhibited antiaging effects via regulation of Sir2/Uth1/TOR signaling pathway.

Availability of Amino Acids Extends Chronological Lifespan by Suppressing Hyper-Acidification of the Environment in Saccharomyces cerevisiae.

The chronological lifespan of Saccharomyces cerevisiae represents the duration of cell survival in the postdiauxic and stationary phases. Using a prototrophic strain derived from the standard auxotrophic laboratory strain BY4742, we showed that supplementation of non-essential amino acids to a synthetic defined (SD) medium increases maximal cell growth and extends the chronological lifespan. The positive effects of amino acids can be reproduced by modulating the medium pH, indicating that amino acids contribute to chronological longevity in a cell-extrinsic manner by alleviating medium acidification. In addition, we showed that the amino acid-mediated effects on extension of chronological longevity are independent of those achieved through a reduction in the TORC1 pathway, which is mediated in a cell-intrinsic manner. Since previous studies showed that extracellular acidification causes mitochondrial dysfunction and leads to cell death, our results provide a path to premature chronological aging caused by differences in available nitrogen sources. Moreover, acidification of culture medium is generally associated with culture duration and cell density; thus, further studies are required on cell physiology of auxotrophic yeast strains during the stationary phase because an insufficient supply of essential amino acids may cause alterations in environmental conditions.

Ganodermasides A and B, two novel anti-aging ergosterols from spores of a medicinal mushroom Ganoderma lucidum on yeast via UTH1 gene.

Two novel ergosterol derivatives, ganodermasides A and B, hydroxylated at C-15 were isolated from the methanol extract of spores of a medicinal mushroom, Ganoderma lucidum, showed to extend the replicative life span of Saccharomyces cerevisiae, a yeast of K6001 strain. The stereostructures of ganodermasides A and B were determined based on the spectroscopic analysis and comparison of spectroscopic data. These new sterols have a 4, 6, 8(14), 22-tetraene-3-one unit with a unique hydroxylation at C-15. The anti-aging activity of these compounds on yeast is comparable to a well-known substance, resveratrol. Based on results of the investigation of the mechanism of biological activity, ganodermasides A and B regulated UTH1 expression in order to extend the replicative life span of yeast.

A novel mitochondrial carnitine-acylcarnitine translocase induced by partial hepatectomy and fasting.

The carnitine-dependent transport of long-chain fatty acids is essential for fatty acid catabolism. In this system, the fatty acid moiety of acyl-CoA is transferred enzymatically to carnitine, and the resultant product, acylcarnitine, is imported into the mitochondrial matrix through a transporter named carnitine-acylcarnitine translocase (CACT). Here we report a novel mammalian protein homologous to CACT. The protein, designated as CACL (CACT-like), is localized to the mitochondria and has palmitoylcarnitine transporting activity. The tissue distribution of CACL is similar to that of CACT; both are expressed at a higher level in tissues using fatty acids as fuels, except in the brain, where only CACL is expressed. In addition, CACL is induced by partial hepatectomy or fasting. Thus, CACL may play an important role cooperatively with its homologue CACT in a stress-induced change of lipid metabolism, and may be specialized for the metabolism of a distinct class of fatty acids involved in brain function.