Analysis and validation of traits associated with a single nucleotide polymorphism Gly364Ser in catestatin using humanized chromogranin A mouse models

Abstract

Objective The human prohormone chromogranin A (CHGA), an index member of the granin family is processed to generate catestatin, a peptide that is hypotensive in action and modulates catecholamine release within the sympathoadrenal system. Hypertensive patients with excess sympathetic activity have diminished catestatin. Often the study of physiological consequences of human genetic variation is confounded by elements such as other variations in obligatory linkage disequilibrium with the variant being studied. Also the phenotype of the variant may be influenced by genetic background that varies amongst individuals. This study addresses the effects of a human catestatin polymorphism (rs9658667) using humanized CHGA mouse models. Methods We created pertinent humanized mouse models wherein the mouse Chga gene locus was replaced by the human ortholog wild-type and the variant versions. This allowed for probing of the effects of catestatin variation in vivo with controls for other variations and global genetic background. Results Both the wild-type and variant human catestatin expressing mouse models were normotensive. The variant catestatin mouse model recapitulated physiological influence of the polymorphism on autonomic traits. These mice had diminished catecholamine, attenuated stress response and increased baroreceptor slopes that would suggest reduced risk of developing hypertension. Elevated plasma glucose, a trait observed in humans was not observed in mice expressing the variant catestatin. Conclusion This functional genomics approach of creating humanized mouse models to study rs9658667 polymorphism recapitulated and validated many of the human trait associations. This approach can also be applied in the study of other human gene polymorphisms.

Animal Models of Hypertension: A Scientific Statement From the American Heart Association

“…Alternatively, the use of bacterial artificial chromosomes, which incorporate hundreds of kilobases of DNA, human chromagranin variants have been analyzed in mouse models, for their ability to reduce the risk of hypertension. 76,77 Gene targeting, resulting in loss of gene function, was also achieved initially in the mouse after the development of embryonic stem cells (ESCs). The gene-targeting construct is introduced by transfection or electroporation into ESCs, and those cells that have been correctly targeted by homologous recombination are selected and injected into blastocysts.…”

Mice overexpressing chromogranin A display hypergranulogenic adrenal glands with attenuated ATP levels contributing to the hypertensive phenotype

“…BP and heart rate were continuously recorded for a period of 24 h at a frequency of 2000 Hz/s. The BP and heart rate for every time point were calculated from 10 s of continuous recording every 5 min and averaging every hour data [25].…”

Chromogranin A pathway: from pathogenic molecule to renal disease

“…The animals are then followed sequentially for 10 weeks, with weekly assessments of blood pressure and hazard ratio using tail-cuff apparatus, as described previously [14]. Weekly blood sampling of operated mice was done by tail vein incision to obtain plasma for creatinine measurements [15].…”