Regulation of Cardiokine Secretion and Cardiac Function by Peptidylglycine α-Amidating Monooxygenase (PAM)

Atrial fibrillation (AF) is the most common arrhythmia and a major cause of complications such as ischemic stroke, heart failure, and atrial remodeling. Its prevalence increases with aging and is associated with risk factors such as obesity, hypertension, diabetes, and cardiovascular diseases. Current treatments often have limited efficacy and significant side effects, underscoring the need for new therapeutic approaches targeting the underlying molecular mechanisms of AF. Calcitonin (CT), a 32-amino acid hormone, is produced by both thyroid C-cells and human atrial cardiomyocytes. CT exerts anti-fibrotic and anti-arrhythmic effects by binding to receptors on atrial fibroblasts. Reduced atrial CT levels, observed in aging and persistent AF, suggest a role in the structural and electrical remodeling of the atrium. However, the mechanisms behind this decline in CT levels remain unclear, limiting its therapeutic potential. C-terminal amidation, a post-translational modification essential for the stability and biological activity of many secreted peptides, including thyroid-derived CT, occurs during CT maturation in thyroid cells. Peptidylglycine α-amidating monooxygenase (PAM), the enzyme responsible for C-terminal amidation, is highly expressed in atrial myocytes, localizing to the endoplasmic reticulum (ER) and Golgi, the primary sites for peptide synthesis. Nevertheless, the function of atrial PAM in atrial peptide amidation has not yet been thoroughly examined. Evidence suggests a connection between PAM and heart rhythm regulation. For example, genome-wide association studies have linked single-nucleotide polymorphisms in the PAM gene to abnormal PR intervals, which increase the risk of AF. We hypothesize that PAM is essential for optimal atrial CT secretion, which is critical for atrial function and the development of AF. To test this hypothesis, we utilized neonatal rat atrial myocytes (NRAM) and neonatal rat atrial fibroblasts (NRVF). We used siRNA targeted to rat PAM to knockdown PAM in NRAM cultures, and collected conditioned media from these cultures. NRVFs were treated with this conditioned media in the presence of TGF-β for 48 hours to assess its effects on fibroblast activation and differentiation. Fibroblast differentiation markers, including fibronectin ( FN1 ), vimentin ( VIM ), and α-smooth muscle actin ( ACTA2 ), were examined by immunoblotting and qRT-PCR. Conditioned media from PAM-depleted NRAMs significantly increased the expression of fibronectin and vimentin proteins, as well as the mRNA levels of FN1, VIM, and ACTA2, compared to media from NRAMs transfected with a scrambled control siRNA. In summary, PAM depletion in atrial myocytes increases fibroblast differentiation, suggesting a critical role for PAM in regulating secretion of anti-fibrotic proteins and potentially atrial CT secretion. These results highlight the potential of PAM as a therapeutic target for AF by mitigating atrial remodeling and improving clinical outcomes. This work was supported by the NIH (HL170223), the U of Arizona Health Sciences Career Development Award, and the UA COM Phoenix Translational Cardiovascular Research Center. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.