Sympathetic Innervation of Human Alpha Cells

Abstract

Autonomic input is critical for the regulation of glucagon secretion to maintain blood glucose levels. Glucagon secretion is abnormal in patients with type 1 diabetes (T1D) and we hypothesize this results from dysfunctional sympathetic innervation of alpha-cells and may be present in at-risk autoantibody positive (AAb+) individuals. To characterize alpha-cell sympathetic innervation, pancreas tail samples were used from age-matched organ donors in three groups: controls (n=6), AAb+ (4), and T1D (4). Fresh frozen 40μm sections or 1-2 cm optically cleared samples were stained with markers for neuroendocrine cells (GCG, INS), total (NCAM)/ sympathetic nerves (tyrosine hydroxylase (TH)), and vascular smooth muscle cells (SMA) followed by confocal and Lightsheet imaging. To determine whether sympathetic fibers were decreased in AAb+ and/or T1D donors, TH+ fiber numbers were counted within islets and the percentage (%) of TH+ fibers/NCAM+ fibers determined. The TH+ fibers/islet were not significantly different between controls (1.5 ± 0.36, n=6), AAb+ (1.2 ± 0.27 (4)), and T1D (1.8 ± 0.57 (4)) donors (p = 0.07, ANOVA) with similar results for TH+ %. TH+ fibers were observed at alpha-cells in all donors. TH+ nerve densities were also similar between islets and exocrine regions between groups. Microarray analysis of single islet transcriptomes obtained using laser microdissection (n=120 islets, 13 control, 12 T1D) showed decreased expression of VMAT2 in insulin+ islets from T1D donors compared to control islets (p=0.047) while insulin- islets in T1D donors had significantly reduced VMAT2 levels compared to control islets (p<0.0001). These data indicate a potential direct mechanism by which the sympathetic nervous system may regulate alpha-cell glucagon secretion with dysregulation of a vesicular monoamine transporter that accumulates monoamines in synaptic vesicles in islets without beta-cells in T1D donors. Sympathetic innervation of alpha-cells could play a direct role in exacerbation of dysregulated glucagon secretion in T1D. Disclosure E.A. Butterworth: None. L.H. Nasif: None. K. Nasif: None. K.N. Carty: None. C.E. Mathews: None. M.A. Atkinson: Other Relationship; Self; Patent Issued. I.C. Gerling: None. M. Campbell-Thompson: None.