Does differential receptor distribution underlie variable responses to a neuropeptide in the lobster cardiac system?

Authors: MUSCATO, AUDREY - Bowdoin College; WALSH, PATRICK - Bowdoin College; PONG, SOVANNARTH - Bowdoin College; PUPO, ALIXANDER - Bowdoin College; Gross, Roni; CHRISTIE, ANDREW - University Of Hawaii; Hull, Joe; DICKINSON, PATSY - Bowdoin College

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2021
Publication Date: 8/13/2021
Citation: Muscato, A.J., Walsh, P., Pong, S., Pupo, A., Gross, R.J., Christie, A.E., Hull, J.J., Dickinson, P.S. 2021. Does differential receptor distribution underlie variable responses to a neuropeptide in the lobster cardiac system? International Journal of Molecular Sciences. 22(16). Article 8703. https://doi.org/10.3390/ijms22168703.
DOI: https://doi.org/10.3390/ijms22168703

Interpretive Summary: The neuronal networks that control rhythmic movements, such as locomotion and respiration, generate consistent recurring output signals that are turned into specific patterns of movement. Rhythmic behaviors, however, need to adapt to fluctuating conditions. This flexibility in signal output is largely driven by neuromodulators, many of which are neuropeptides. The American lobster heartbeat is controlled by the cardiac ganglion, a simple neuronal network that is capable of responding to the complex modulation required to meet the physiological demands placed on the lobster heart. The allatostatin type C (AST-C) group of peptides have a number of modulatory effects on the cardiac system. The responses though can vary across lobsters. To gain insights into the potential mechanisms that may contribute to the variability in the AST-C responses, the diversity of AST-C receptor (ASTCR) expression in the cardiac ganglion was assessed. Although transcripts encoding four structurally distinct ASTRs were amplified, only ASTCR1 and ASTCR2 localized to the plasma membrane when expressed as fluorescent chimeras in cultured insect cells. Incubation of AST-C peptides with recombinantly expressed ASTCR1 and ASTCR2 led to specific receptor-peptide interactions that resulted in receptor activation, indicating that both receptors are capable of mediating AST-C peptide activity in vivo. Intriguingly, when the expression levels of the respective ASTCRs in the cardiac ganglion were examined in relation to cardiac responses, a significant negative correlation with the amplitude of the response following AST-C application was only observed with ASTCR1, suggesting that the distribution of ASTCR1 may play a role in how the AST-C signal is processed.

Technical Abstract: Central pattern generators produce rhythmic behaviors independently of sensory input; however, their outputs can be modulated by neuropeptides, thereby allowing for functional flexibility. We investigated the effects of C-type allatostatins (AST-C) on the cardiac ganglion (CG), which is the central pattern generator that controls the heart of the American lobster, Homarus americanus, to identify the biological mechanism underlying the significant variability in individual responses to AST-C. We proposed that the presence of multiple receptors, and thus differential receptor distribution, was at least partly responsible for this observed variability. Using transcriptome mining and PCR-based cloning, we identified four AST-C receptors (ASTCRs) in the CG; we then characterized their cellular localization, binding potential, and functional activation. Only two of the four receptors, ASTCR1 and ASTCR2, were fully functional GPCRs that targeted to the cell surface and were activated by AST-C peptides in our insect cell expression system. All four, however, were amplified from CG cDNAs. Following the confirmation of ASTCR expression, we used physiological and bioinformatic techniques to correlate receptor expression with cardiac responses to AST-C across individuals. Expression of ASTCR1 in the CG showed a negative correlation with increasing contraction amplitude in response to AST-C perfusion through the lobster heart, suggesting that the differential expression of ASTCRs within the CG is partly responsible for the specific physiological response to AST-C exhibited by a given individual lobster.