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. 2016 Oct 25;17(5):1227-1237.
doi: 10.1016/j.celrep.2016.09.086.

Vitamin D Promotes Protein Homeostasis and Longevity via the Stress Response Pathway Genes skn-1, ire-1, and xbp-1

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Free PMC article

Vitamin D Promotes Protein Homeostasis and Longevity via the Stress Response Pathway Genes skn-1, ire-1, and xbp-1

Karla A Mark et al. Cell Rep. .
Free PMC article

Abstract

Vitamin D has multiple roles, including the regulation of bone and calcium homeostasis. Deficiency of 25-hydroxyvitamin D, the major circulating form of vitamin D, is associated with an increased risk of age-related chronic diseases, including Alzheimer's disease, Parkinson's disease, cognitive impairment, and cancer. In this study, we utilized Caenorhabditis elegans to examine the mechanism by which vitamin D influences aging. We found that vitamin-D3-induced lifespan extension requires the stress response pathway genes skn-1, ire-1, and xbp-1. Vitamin D3 (D3) induced expression of SKN-1 target genes but not canonical targets of XBP-1. D3 suppressed an important molecular pathology of aging, that of widespread protein insolubility, and prevented toxicity caused by human β-amyloid. Our observation that D3 improves protein homeostasis and slows aging highlights the importance of maintaining appropriate vitamin D serum levels and may explain why such a wide variety of human age-related diseases are associated with vitamin D deficiency.

Keywords: Alzheimer’s disease; Ceanorhabditis elegans; IRE-1; SKN-1; XBP-1; insoluble protein; lifespan. aging; protein aggregation; proteostasis; vitamin D.

Figures

Figure 1
Figure 1. C. elegans fed D3 are capable of synthesizing the biologically active form of D3, 1,25-(OH)2D3, and lipid extracts derived from D3-fed worms can activate human vitamin D receptor (VDR) transcriptional activity
(A) Diagram of the human vitamin D metabolic pathway. (B) Lipid extracts derived from D3-fed worms activated human VDR transcriptional activity as evidenced by increased luciferase activity compared to control-treated worms. Data are presented as relative luciferase units. Error bars indicate mean + standard error of the mean (SEM) (* P< 0.05, unpaired t-test, n=3). (C) Liquid Chromatography/Mass Spectrometry (LC-MS) extracted ion (MRM of m/z 574→314) chromatogram of detected 1,25-(OH)2D3 from lipid extracts of wild-type (N2) worms synchronously grown until the second day of adulthood on either control or D3 (100 µM) NGM plates. The D3-fed lipid extracts revealed a signal identical to the 1,25-(OH)2D3 standard, indicated by the boxed green signal. There was no 1,25-(OH)2D3 detected in the control lipid extracts.
Figure 2
Figure 2. Vitamin D3 requires SKN-1, IRE-1, and XBP-1 stress response genes for lifespan extension
(A) Kaplan-Meier survival curves of N2 hermaphrodite worms exposed to increasing concentrations of D3 from day 1 of adulthood (P< 0.0001; log-rank test). (B) D3 (25–250 µM) extended the lifespan of CF1038 [daf-16(mu86)] worms, which lack functional DAF-16 protein, when treated from day 1 of adulthood at 20°C (P<0.0001, log-rank test). (C) D3 (25–100 µM) feeding resulted in marginal lifespan extension in PS3551 [hsf-1(sy441)] (P=0.0090, Log-rank test). (D) D3 (50 µM) treatment resulted in little or no lifespan extension of the EU31 [skn-1(zu135) IV/nT1 [unc-?(n754) let-?]] worms (P= 0.002, log-rank test). (E) D3 (50 µM) treatment shortens the lifespan in RE666 [ire-1(v33)] mutant worms (P<0.0001, log-rank test). (F) D3 (50 µM) treatment does not extend lifespan in SJ17 [xbp-1(zc12); zcIs4] mutant worms (P=0.142, log-rank test).
Figure 3
Figure 3. Vitamin D3 induced activation of the SKN-1 target gene gst-4 is IRE-1-dependent
(A) Quantification of a reporter strain (CL2166) containing gst-4p::GFP following D3 feeding (25–100 µM) from L1 larval stage and scored at L4 larval stage at 16oC. Data is represented as GFP Fluorescence (arbitrary units, a.u.). (B) Reducing SKN-1 by skn-1 RNAi prevents the D3-induced increase in pgst-4::GFP fluorescence. Data are presented as percent paralyzed. DMSO bars represent the equivalent amount of solvent used for D3 feeding. (C) Relative gst-4 mRNA levels (mean + SEM) in N2 worms fed D3 (100µM). ire-1 RNAi prevents the D3-induced increase in gst-4 mRNA levels. Data are presented as relative mRNA levels. (* P<0.05, unpaired t-test, n=3).
Figure 4
Figure 4. Vitamin D3 feeding prevents the accumulation of insoluble proteins in aged C. elegans and slows protein aggregation-associated paralysis
(A) SDS-PAGE of the SDS-insoluble fraction of cellular proteins from 2 and 8 day adult TJ1060 worms grown at 25°C. D3 (100 µM) prevents the accumulation of SDS-insoluble proteins in aged worms. (B) Gene ontology (GO) analysis of proteins observed in the insoluble fraction of old worms that were suppressed by D3 treatment (as determined by quantitative mass spectrometry/MS1 Filtering). Classification is as assigned by Klusters of Orthologous Groups (KOG). (C–D) Mass spectrometry quantification of unique proteins in (C) young (day 2) and aged (day 8) control treated worms, and (D) comparison between proteins identified in aged (day 8) D3-treated and aged control worms. (E) Exposing worms to D3 (10–100 µM) suppresses the paralysis phenotype associated with protein aggregation in CL4176 expressing Aβ(3–42) in the muscle after 34 hours at 25°C. (F) D3 treatment (10–100 µM) rescues the paralysis in the strain HE250 [unc-52(e669su250)] after 42 hours at 25°C. (G) Reducing SKN-1 by skn-1 RNAi prevents the D3-induced suppression of paralysis in the temperature-sensitive strain HE250. Data are presented as percent paralyzed. DMSO bars represent the equivalent amount of solvent used for D3 treatment (* P<0.05 Multiple t-tests comparison, Holm-Sidak method, alpha=5.0%). Relative gst-4 mRNA levels (mean + SEM) in HE250 (H) and CL4176 (I) worms fed D3 (100µM) (* P<0.05, unpaired t-test). Error bars indicate mean ± standard error of the mean (SEM) and represent the average of three to four independent experiments, 30–40 worms per group, per experiment.

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