title: Health span and life span in transgenic mice with modulated DNA repair.
abstract: One way to better understand the contribution of DNA repair, DNA damage, and mutagenesis in aging would be to enhance DNA repair activity, lower DNA damage, and lower mutagenesis. Because the repair protein O6-methylguanine-DNA methyltransferase (MGMT) acts alone and stoichiometrically, the human MGMT (hMGMT) cDNA was selected to test the feasibility of enhancing DNA repair activity in transgenic mice. MGMT activity is largely responsible for ameliorating the deleterious effects of O6-methylguanine (O6mG) lesions in DNA in a direct reversal mechanism. A transgene was constructed consisting of a portion of the human transferrin (TF) promoter and hMGMT cDNA such that hMGMT is expressed in transgenic mouse brain and liver. Expression of hMGMT was associated with a significant reduction in the occurrence of an age-related hepatocellular carcinoma in male mice at 15 months of age. Longitudinal and cross-sectional studies were initiated to determine whether the reduced incidence of hepatocellular carcinoma would impact median or maximum life span. The cross-sectional study performed on 15-month-old male animals confirmed the reduced occurrence of spontaneous hepatocellular carcinoma. At 30 months of age, however, the occurrence of hepatocellular carcinoma in at least one transgenic line was similar to that for nontransgenic animals. The longitudinal study is ongoing; however, at present no significant differences in life span have been detected. Tissues expressing the MGMT transgene also displayed greater resistance to alkylation-induced tumor formation. These results suggest that transgenes can be used to direct enhanced DNA repair gene expression and that enhanced expression can protect animals from certain spontaneous and induced tumors.
authors.affiliation: Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, 78229-3900, USA. walter@uthscscsa.edu
authors.forename: C A
authors.initials: CA
authors.lastname: Walter
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Zhou
authors.forename: D
authors.initials: D
authors.lastname: Manguino
authors.forename: Y
authors.initials: Y
authors.lastname: Ikeno
authors.forename: R
authors.initials: R
authors.lastname: Reddick
authors.forename: J
authors.initials: J
authors.lastname: Nelson
authors.forename: G
authors.initials: G
authors.lastname: Intano
authors.forename: D C
authors.initials: DC
authors.lastname: Herbert
authors.forename: C A
authors.initials: CA
authors.lastname: McMahan
authors.forename: M
authors.initials: M
authors.lastname: Hanes
mesh_terms: D017668:Age of Onset; D000477:Alkylating Agents / Q000633:toxicity; D000818:Animals; D001921:Brain / Q000201:enzymology; D002273:Carcinogens / Q000633:toxicity; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D004790:Enzyme Induction; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis; D008099:Liver / Q000201:enzymology; D008114:Liver Neoplasms, Experimental / Q000201:enzymology / Q000235:genetics / Q000517:prevention & control; D008136:Longevity / Q000235:genetics*; D008168:Lung / Q000201:enzymology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000502:physiology; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014168:Transferrin / Q000235:genetics; D019076:Transgenes
chemical_list: D000477:Alkylating Agents; D002273:Carcinogens; D018076:DNA, Complementary; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D014168:Transferrin; D006147:Guanine; C008449:O-(6)-methylguanine; D019853:O(6)-Methylguanine-DNA Methyltransferase