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. 2016 Jul 27;2(7):e1600031.
doi: 10.1126/sciadv.1600031. eCollection 2016 Jul.

Nuclear respiratory factor 1 and endurance exercise promote human telomere transcription

Aurélie Diman  1 , Joanna Boros  1 , Florian Poulain  1 , Julie Rodriguez  2 , Marin Purnelle  3 , Harikleia Episkopou  1 , Luc Bertrand  4 , Marc Francaux  2 , Louise Deldicque  2 , Anabelle Decottignies  1
Affiliations

Nuclear respiratory factor 1 and endurance exercise promote human telomere transcription

Aurélie Diman et al. Sci Adv. .

Abstract

DNA breaks activate the DNA damage response and, if left unrepaired, trigger cellular senescence. Telomeres are specialized nucleoprotein structures that protect chromosome ends from persistent DNA damage response activation. Whether protection can be enhanced to counteract the age-dependent decline in telomere integrity is a challenging question. Telomeric repeat-containing RNA (TERRA), which is transcribed from telomeres, emerged as important player in telomere integrity. However, how human telomere transcription is regulated is still largely unknown. We identify nuclear respiratory factor 1 and peroxisome proliferator-activated receptor γ coactivator 1α as regulators of human telomere transcription. In agreement with an upstream regulation of these factors by adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), pharmacological activation of AMPK in cancer cell lines or in normal nonproliferating myotubes up-regulated TERRA, thereby linking metabolism to telomere fitness. Cycling endurance exercise, which is associated with AMPK activation, increased TERRA levels in skeletal muscle biopsies obtained from 10 healthy young volunteers. The data support the idea that exercise may protect against aging.

Keywords: AMPK; NRF1; TERRA; Telomere; exercise.

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Figures

Fig. 1
Fig. 1. NRF1 binds human subtelomeric promoters.
(A) Predicted NRF1 binding sites on human subtelomeres (gray bars). Black bars indicate putative TSS based on the study by Nergadze et al. (5). Black triangles indicate telomeres. (B) NRF1 binding at subtelomeres of LB37 cells. Graph shows fold enrichment over IgG. Error bars indicate SD (n = 3). (C) qRT-PCR analysis of TERRA in LB37 cells for the indicated chromosome ends. TERRA cDNA levels were first normalized to β2M cDNA and then to the relative expression level of 1q-2q-4q-10q-13q-22q TERRA. Error bars indicate SD (three independent RNA extractions). (D) Relative 15q TERRA expression in LB37 and Huh-7 cell lines (normalized first to β2M cDNA and then to LB37). (E) NRF1 binding assessed by ChIP on six loci spread onto 15q subtelomere in LB37 and Huh-7 cell lines. Graph shows fold enrichment over IgG. Error bars indicate SD (n = 3).
Fig. 2
Fig. 2. Endurance exercise up-regulates TERRA in human muscle.
(A) Design of the in vivo experiment. (B) Blood lactate concentrations (mM) before (gray) and at the end (black) of exercise in subjects (S) (50% VO2 peak, low-intensity exercise; 75% VO2 peak, high-intensity exercise). (C) Representative Western blots of ACC phosphorylation (P-ACC) in B1, B2, and B3 biopsies from S5 (high lactate), S6 (medium lactate), and S12 (low lactate). Total ACC was used to evaluate the P-ACC/ACC ratio, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used as a loading control. (D) P-ACC/ACC ratios in B2 and B3 normalized to B1 for all subjects. (E) P-ACC/ACC ratios plotted against blood lactate concentration after exercise. (F) PGC-1α abundance in nuclear fractions from S12, S6, and S5 biopsies normalized to Ku80 and to matching B1. (G) PGC-1α cDNA normalized to β2M cDNA and to matching B1. (H) qRT-PCR analysis of TERRA (15q, 16p, and 1q-2q-4q-10q-13q-22q) in B2 and B3, normalized to β2M cDNA and to matching B1. (I) Average induction of TERRA (all three qRT-PCRs pooled) in B3 compared to matching B1 for 50% VO2 peak group (n = 5) and 75% VO2 peak group (n = 5). Error bars indicate SD. (J) TERRA fold induction in B3 plotted against blood lactate concentration after exercise. (K) TERRA-FISH (red) and TRF2 detection (green) in muscle biopsies. Blue, 4′,6-diamidino-2-phenylindole (DAPI). Scale bar, 5 μm.
Fig. 3
Fig. 3. NRF1 and AMPK/PGC-1α axis promote human telomere transcription.
(A) NRF1 protein in siLuci- and siNRF1-treated Huh-7 cells; TERRA cDNA normalized to β2M cDNA and siLuci (n = 3). (B) NRF1/ΔC NRF1 overexpression in Huh-7 cells; TERRA cDNA normalized to β2M cDNA and to NRF1-overexpressing cells (n = 3). (C) Transcriptional activity of 10q promoter in Huh-7 cells overexpressing increasing amounts of NRF1/ΔC NRF1 (n = 3). (D and E) Phenformin treatment in Huh-7: ACC phosphorylation and PGC-1α nuclear translocation. Scale bar, 100 μm. (F) qRT-PCR analyses of TERRA, PGC-1α, and hTR upon phenformin treatment normalized to β2M cDNA and to untreated cells (n = 3). (G) Transcriptional activity of 10q promoter in phenformin-treated Huh-7 cells overexpressing NRF1 or ΔC NRF1 normalized to pcDNA3-transfected control cells (n = 5). (H) Impact of NRF1 binding site mutation on 10q transcriptional activity. Data were normalized to untreated cells transfected with wild-type (WT) 10q promoter and pcDNA3 (n = 4). Empty: No promoter. (I) 10q transcriptional activity upon mPGC-1α overexpression, in combination with NRF1/ΔC NRF1. Data were normalized to pcDNA3-transfected/adenovirus–green fluorescent protein (Ad-GFP)–transduced cells (n = 6). (J) TERRA cDNA in mPGC-1α–overexpressing Huh-7 normalized to β2M cDNA and Ad-GFP control cells (n = 5). (A to J) Error bars indicate SD. (K) TIF formation upon NRF1 knockdown in Huh-7 cells. Telomeres were detected by FISH (red) and DNA damage with 53BP1 antibody (green). Data are representative of three independent transfections. Scale bar, 5 μm.
Fig. 4
Fig. 4. AMPK activation in human myotubes induces NRF1-dependent increase in TERRA levels.
(A) TERRA-FISH (green) combined with telomeric DNA FISH (red) in myotubes. Blue, DAPI. Scale bar, 5 μm. (B) Quantification of (A) on 25 nuclei. (C) ACC phosphorylation in myotubes treated with either AICAR, metformin, or phenformin. (D) qRT-PCR analysis of TERRA levels in treated myotubes normalized to β2M cDNA and to untreated cells. Error bars indicate SD (n = 4). (E) Western blot analysis of NRF1 knockdown in myotubes. (F) qRT-PCR analysis of TERRA in siNRF1-treated myotubes and upon phenformin treatment. Values were normalized to β2M cDNA and to siLuci-treated cells without phenformin. Error bars indicate SD (n = 3). (G) Unified theory of aging (34) revisited with data from this study (green). See text for details.
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