Long human CHGA flanking chromosome 14 sequence required for optimal BAC transgenic “rescue” of disease phenotypes in the mouse Chga knockout

Abstract

Chromogranin A (CHGA) plays a catalytic role in formation of catecholamine storage vesicles and also serves as precursor to the peptide fragment catestatin, a catecholamine secretory inhibitor whose expression is diminished in the hypertensive individuals. We previously reported the hypertensive, hyperadrenergic phenotype of Chga−/− knockout (KO) mice and rescue by the human ortholog. In the present study, we compare two humanized CHGA mouse models. Into the Chga null background, by bacterial artificial chromosome transgenesis human CHGA transgene has been introduced. Both lines have the complete ∼12 kbp CHGA gene integrated stably in the genome but have substantial differences in CHGA expression, as well as consequent sympathochromaffin biochemistry and physiology. A mouse model with longer-insert Hum CHGA31 displays integration encompassing not only CHGA but also long human flanking sequences. This is in contrast to mouse model Hum CHGA19 with limited flanking human sequence co-integrated. As a consequence, Hum CHGA19 mice have normal though diminished pattern of spatial expression of CHGA, and 14-fold lower circulating CHGA, with failure to rescue KO phenotypes to normalcy. In the longer-insert Hum CHGA31 mice, catecholamine secretion, exaggerated responses to environmental stress, and hypertension were all alleviated. Promoter regions of the transgenes in both Hum CHGA19 and Hum CHGA31 display minimal CpG methylation, weighing against differential “position effects” of integration, and thus suggesting that lack of cis elements required for optimal CHGA expression occurs in Hum CHGA19 mice. Such “humanized” CHGA mouse models may be useful in probing the physiological consequences of variation in CHGA expression found in humans, with consequences for susceptibility to hypertension and cardiovascular disease.