Title

Genetic and nutritional reductions in peptide amidation result in neuroendocrine deficits in mice

Date of Completion

January 2009

Keywords

Biology, Neuroscience|Biology, Genetics|Health Sciences, Nutrition

Degree

Ph.D.

Abstract

Genetic and pharmacological manipulation demonstrated the neurological and metabolic importance of specific amidated peptides and highly conserved enzymes involved in peptide synthesis. Deletion of the only mammalian peptide amidating enzyme, peptidylglycine a-amidating monooxyenase (PAM), resulted in developmental lethality. The goal of this dissertation was to investigate the neurophysiological importance of haplioinsufficient reductions in PAM in mice following genetic and nutritional manipulation. It was hypothesized that physiological functions requiring multiple amidated peptides would be most sensitive to genetic and nutritional reductions in the posttranslational peptide amidation which is necessary to confer their bioactivity: namely temperature regulation, vasoconstriction, seizure sensitivity, and anxiety-like behavior. PAM requires copper to amidate peptides; copper is also critical for many physiological functions which require multiple amidated peptides. As a result, it was hypothesized that supplementation of dietary copper availability would improve peptide amidation and physiological functions requiring multiple amidated peptides. Conversely, it was hypothesized that reductions in dietary copper availability would impair peptide amidation and physiological functions requiring multiple amidated peptides. To address these hypotheses, dietary copper availability was manipulated in mice heterozygous for the PAM gene (PAM+/-) and their wild-type (WT) littermates. ^ Impairments in physiological function were identified in PAM+/- mice compared to their WT littermates at multiple levels. Temperature regulation in PAM+/- mice was impaired with acute cold exposure due to a lack of peripheral vasoconstriction. Neurological function was also impaired in PAM+/--mice at two levels: (1) increased sensitivity to acute pharmacologically-induced seizures; and (2) increased anxiety-like behavior in the elevated zero maze. Variations in dietary copper availability altered peptide amidation and physiological function. Dietary copper supplementation improved temperature regulation and vasoconstriction, and reduced anxiety-like behavior in PAM+/- mice. Copper deficient WT mice exhibited the following deficits: (1) impaired peptide amidation; (2) impaired temperature regulation and vasoconstriction; (3) increased seizure sensivity; (4) increased anxiety-like behavior. Surprisingly, copper metabolism was altered at multiple levels in PAM+/- mice compared to their WT littermates maintained on a copper-adequate control diet. Together, these results demonstrate a novel gene-nutrient interaction between PAM and copper whose balance alters multiple physiological functions. ^