The mammalian protein isoaspartyl methyltransferase (PIMT) specifically modifies abnormal protein aspartyl residues that have arisen spontaneously in aging proteins. The experiments of this project test the hypothesis that mammalian PIMT plays a role in repairing or degrading damaged cellular proteins that this function is particularly important for terminally differentiated cells and for cells approaching senescence. In situ hybridization will be used to identify cellular patterns of PIMT gene expression in brain and testis, tissues with large numbers of postmitotic cells and high levels of PIMT activity. The experiments will identify stages of sperm differentiation characterized by increased PIMT expression. The studies with brain tissue will identify groups of neurons with elevated PIMT levels. Similar studies will be done with brain tissue from aging animals to test whether changes in PIMT expression accompany the loss of neuronal function during aging. PIMT levels will be experimentally manipulated in cultured cell models to determine the consequences of PIMT depletion and overexpression on cellular physiology. Permanent cell lines that either overexpress or are deficient in PIMT will be constructed by transfection with high level expression plasmids containing the PIMT gene sequence in either sense or antisense orientations. Experiments will measure the effects of PIMT dosage on cellular protein metabolism, ability to survive nutritional stress, tendency to enter senescence and differentiation to a neuronal phenotype. A biochemical model will be used to identify roles for the PIMT in protein repair or degradation. Radiolabeled calmodulins will be converted to isomerized forms in an artificial aging protocol. These substrates will be injected into Xenopus oocytes and the stability of the protein will be measured in the absence and presence of methylation inhibitors to determine if carboxyl methylation decreases or increases protein stability. Peptide mapping will be used to monitor any repair reactions. By allowing dysfunctional proteins to accumulate in cells, PIMT malfunction could contribute to infertility and neurodegenerative disorders associated with aging. For example, L-isoaspartyl residues have been identified at several locations in beta-amyloid peptides from Alzheimer-diseased brains, raising the possibility that deficiencies in methylation contribute to the aberrant processing reactions in that disease. The elucidation of the methylation-mediated pathway and the identification of effectors that increase its efficiency could have potential value in treating age-related disorders which involve defects in protein metabolism.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
5R01AG008109-12
Application #
2442224
Study Section
Physiological Chemistry Study Section (PC)
Program Officer
Finkelstein, David B
Project Start
1985-08-30
Project End
1999-06-30
Budget Start
1997-07-01
Budget End
1998-06-30
Support Year
12
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Boston College
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
045896339
City
Chestnut Hill
State
MA
Country
United States
Zip Code
02467
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O'Connor, M B; Galus, A; Hartenstine, M et al. (1997) Structural organization and developmental expression of the protein isoaspartyl methyltransferase gene from Drosophila melanogaster. Insect Biochem Mol Biol 27:49-54
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