Chemical genetic screen identifies lithocholic acid as an anti-aging compound that extends yeast chronological life span in a TOR-independent manner, by modulating housekeeping longevity assurance processes

Abstract

In chronologically aging yeast, longevity can be extended by administering a caloric restriction (CR) diet or some small molecules. These life-extending interventions target the adaptable target of rapamycin (TOR) and cAMP/protein kinase A (cAMP/PKA) signaling pathways that are under the stringent control of calorie availability. We designed a chemical genetic screen for small molecules that increase the chronological life span of yeast under CR by targeting lipid metabolism and modulating housekeeping longevity pathways that regulate longevity irrespective of the number of available calories. Our screen identifies lithocholic acid (LCA) as one of such molecules. We reveal two mechanisms underlying the life-extending effect of LCA in chronologically aging yeast. One mechanism operates in a calorie availability-independent fashion and involves the LCA-governed modulation of housekeeping longevity assurance pathways that do not overlap with the adaptable TOR and cAMP/PKA pathways. The other mechanism extends yeast longevity under non-CR conditions and consists in LCA-driven unmasking of the previously unknown anti-aging potential of PKA. We provide evidence that LCA modulates housekeeping longevity assurance pathways by suppressing lipid-induced necrosis, attenuating mitochondrial fragmentation, altering oxidation-reduction processes in mitochondria, enhancing resistance to oxidative and thermal stresses, suppressing mitochondria-controlled apoptosis, and enhancing stability of nuclear and mitochondrial DNA.

Unopposed mitochondrial fission leads to severe lifespan shortening

“…The former is regarded as a model for dividing mammalian cells (i.e., stem cells), while the latter can be utilized as a model for non-dividing mammalian cells (i.e., neurons). 29,30 We found that, compared with the WT, replicative lifespan is significantly reduced in Δmgm1 cells (Δmgm1: 11 generations vs. WT: 23 generations) (Fig. 4A).…”

Mechanism of liponecrosis, a distinct mode of programmed cell death

“…This pathway stimulates transcription of the RSB1 gene; the resulting increased abundance of Rsb1p promotes further reduction of PE in the outer leaflet of the PM by (1) enhancing a stimulating effect of Rsb1p on the Lem3p-dependent transport of PE from the outer leaflet to the inner (intracellular) leaflet of the PM; and (2) amplifying an inhibitory effect of Rsb1p on the Yor1p-dependent transport of PE within the PM bilayer in the opposite direction. An ensuing depletion of PE in the outer leaflet of the PM elevates the permeability of this cellular membrane for small molecules (such as propidium iodide 1,71 ), thereby contributing to the commitment of yeast to liponecrotic PCD.…”

Lithocholic bile acid accumulated in yeast mitochondria orchestrates a development of an anti-aging cellular pattern by causing age-related changes in cellular proteome

“…[3][4][5][6]16,20,25,31,33,56 Of note, we found that a treatment of yeast cells with LCA alters the agerelated chronology of these mitochondrial processes. 5,36,38,[68][69][70] We therefore hypothesized that LCA may impact not only the levels of numerous mitochondrial proteins but also the levels of proteins in cellular locations outside mitochondria. To validate our hypothesis, we used quantitative mass spectrometry to compare proteins that were recovered in total lysates of WT cells cultured in the presence of LCA or in its absence.…”

“…These cellular processes include the following: (1) glycogen degradation; (2) the glycolytic pathway; (3) the pentose phosphate pathway; (4) pyruvate conversion to acetyl-CoA; (5) the maintenance of redox balance between NAD and NADH with the help of carnitine and glycerol-3-phosphate shuttles; (6) ROS detoxification; (7) stress response; (8) glutathione synthesis; (9) gluconeogenesis; (10) ethanol formation; (11) the synthesis and hydrolytic degradation of triacylglycerols (TAG) and ergosteryl esters (EE), the 2 major neutral lipids; (12) the synthesis of various amino acids; (13) nucleotide synthesis; (14) the assembly of the 40S and 60S ribosomal subunits from numerous protein components whose levels were altered by LCA; and (15) proteasomal and vacuolar protein degradation. 4,5,39,41,38,71,72 We then subjected cellular proteins whose levels were changed in yeast grown in a medium supplemented with LCA to bioinformatic analysis with the help of the SPELL online search engine, 51 as described above for mitochondrial proteins. Just as our bioinformatic analysis of mitochondrial proteins revealed (see above), we found that each of the cellular proteins whose level was altered in yeast cultured with LCA belongs to the following 2 multi-clustered regulons: (1) the PMD regulon, which consisted of the rho 0 (Rtg2p governed) cluster, S1 cluster, general TCA cycle dysfunction cluster, kgd1D, kgd2D or lpd1D cluster, yme1Dmdl1D Figure 2.…”

“…Yeast cells for these experiments were cultured under caloric restriction (CR) conditions on 0.2% glucose rather than under non-CR conditions on 2% glucose. We chose CR conditions for the following reasons: (1) mitochondria, the organelles whose LCA-driven ability to operate as signaling compartments in yeast chronological aging we investigated in this study, are significantly more abundant and functionally active in yeast cells limited in calorie supply than they are in yeast cells on a high-calorie diet; 37,38 …”