Abstract
Chromogranin A (CHGA) has a crucial role in formation of regulated secretory granules in neuroendocrine tissues and is also a prohormone that is proteolytically processed into peptides with diverse and complex actions. CHGA and several of its peptide products, including catestatin and pancreastatin, are implicated in pathogenesis of essential hypertension, insulin resistance, and the metabolic syndrome. The Chga knockout mouse (Chga KO) displays severe hypertension coupled with reduction in size, number, and density of regulated secretory granules. We performed genome-wide transcriptome profiling in Chga KO adrenal gland and liver for insight into biochemical and physiological systems altered in this monogenic mouse model of hypertension. Adrenal gene expression pathway prediction of enhanced insulin sensitivity (P = 0.03) in Chga KO was confirmed with glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR) measurements: blood glucose was normal in Chga KO, blood insulin was reduced 4.5-fold (P < 0.0001), and HOMA-IR was decreased 3.8-fold (P < 0.002). Remarkably, such observations conclusively dissociate fundamental features of the metabolic syndrome in this monogenic hypertension model. Exogenous pancreastatin treatment restored insulin sensitivity in the Chga KO to near-normal levels. Gene expression predictions of decreased adrenal cholesterol biosynthesis (P < 0.001) and increased hepatic cholesterol biosynthesis (P < 0.001) were verified with tissue total cholesterol assays: Chga KO adrenal cholesterol decreased 1.8-fold (P = 0.039) and hepatic cholesterol increased 1.8-fold (P = 0.018). Transcriptional regulatory network prediction identified sets of transcription factors that may provide insight into the unclear mechanistic links among CHGA, cholesterol, insulin sensitivity, and the metabolic syndrome. These experiments demonstrate, for the first time, that genetic variation at the CHGA locus impacts insulin sensitivity and tissue cholesterol levels in an intact, living organism. The Chga KO may constitute a unique model for studying the relationship between the CHGA locus and disease phenotypes of the metabolic syndrome.