Activation of AMPK prevented H 2 O 2 ‐induced senescence. A to D: H 2 O 2 ‐treated NIH 3T3 cells were incubated in complete medium with metformin (Met, 5 to 10 mM ) or berberine ( BBR , 5 to 10 μM) for 3 days. (A) Representative images from immunoblot assays against pAMPK α (Thr172), AMPK α1, pACC (Ser79), and β‐actin. (B) Relative fold‐changes in mRNA levels of CPT ‐1 and FAS as determined by qRT ‐ PCR . (C) Representative images of SA ‐β‐Gal staining of cells (left), and percentages of SA ‐β‐Gal‐positive cells. D‐F: NIH 3T3 cells were treated with H 2 O 2 and incubated with Met (10 mM ), BBR (10 μM) and an AMPK inhibitor, Compound C ( CC , 10 μM), alone or in combination for 3 days. (D) Representative images from immunoblot assays. (E) Relative mRNA levels of CPT ‐1 and FAS as determined by qRT ‐ PCR . (F) Representative images of SA ‐β‐Gal staining of cells (left) and percentages of SA ‐β‐Gal‐positive cells (right). G‐I: NIH 3T3 cells without H 2 O 2 treatment were used. (G) The decrease in AMPK activity in DN ‐ AMPK ‐expressing NIH 3T3 cells was shown by the decrease in AMPK α phosphorylation. (H) Representative images of SA ‐β‐Gal staining of the nontransfected cells with or without CC (upper) and cells transfection with DN ‐ AMPK (lower). (I) The percentages of SA ‐β‐Gal‐positive cells were calculated based on the images represented in H. (J) H 2 O 2 ‐treated cells incubated with or without Met (10 mM ) or BBR (10 μM) for 3 days, representative images of SA ‐β‐Gal staining of cells transfected with empty vector (upper) or DN ‐ AMPK (lower). (K) The percentages of SA ‐β‐Gal‐positive cells were calculated based on the images presented in J. * P