Cell-type specific knockout of peptidylglycine α-amidating monooxygenase reveals specific behavioral roles in excitatory forebrain neurons and cardiomyocytes.

Neuropeptides and peptide hormones play a crucial role in integrating the many factors that affect physiologic and cognitive processes. The potency of many of these peptides requires an amidated amino acid at the C-terminus; a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), catalyzes this modification. Anxiety-like behavior is known to be altered in mice with a single functional Pam allele (Pam+/- ) and in mice unable to express Pam in excitatory forebrain neurons (PamEmx1-cKO/cKO ) or in cardiomyocytes (PamMyh6-cKO/cKO ). Examination of PAM-positive and glutamic acid decarboxylase 67 (GAD)-positive cells in the amygdala of PamEmx1-cKO/cKO mice demonstrated the absence of PAM in pyramidal neurons and its continued presence in GAD-positive interneurons, suggestive of altered excitatory/inhibitory balance. Additional behavioral tests were used to search for functional alterations in these cell-type specific knockout mice. PamEmx1-cKO/cKO mice exhibited a less focused search pattern for the Barnes Maze escape hole than control or PamMyh6-cKO/cKO mice. While wildtype mice favor interacting with novel objects as opposed to familiar objects, both PamEmx1-cKO/cKO and PamMyh6-cKO/cKO mice exhibited significantly less interest in the novel object. Since PAM levels in the central nervous system of PamMyh6-cKO/cKO mice are unaltered, the behavioral effect observed in these mice may reflect their inability to produce atrial granules and the resulting reduction in serum levels of atrial natriuretic peptide. In the sociability test, male mice of all three genotypes spent more time with same-sex stranger mice; while control females showed no preference for stranger mice, female PamEmx1-cKO/cKO mice showed preference for same-sex stranger mice in all trials.