SAT-348 Overexpression of the Notch Intracellular Domain Results in Abnormal Adrenal Development.

Abstract

In the adrenal gland, stem and progenitor cells reside in the capsule and the outer part of the cortex, respectively. The newly formed cortical cells from stem/progenitor cells move inward to the corticomedullary boundary during development. Throughout this developmental process, adrenocortical cells express specific marker genes at different stages which lead to concentric zones of the adrenal cortex (zonation). In mice, the majority of the functional cortex are definitive zones whereas cortical cells in the corticomedullary boundary form the X-zone, which is considered the aged cell population in the cortex and undergoes regression over time. Disruption of signaling pathways such as Wnt, Hedgehog and TGF-beta can cause abnormalities of the developmental process of the adrenal cortex, which may lead to malfunction or malignancy of the adrenal gland. The role of Notch, another key signaling pathway, in adrenal development has not yet been fully studied. Notch signaling pathway involves a variety of gene regulatory mechanisms that control cell proliferation, differentiation, and apoptosis. Although key molecules in Notch signaling pathways are expressed both in the adrenal cortex and in the medulla, the inhibition of canonical Notch signaling only leads to minor/limited effects on the function or the structure of the adrenal gland. We confirmed these observations using Sf1-Cre mediated tissue-specific knockout mouse model that lacks Hes1, one of the most common Notch target genes, in cortical cells in the adrenal gland. Immunostaining with proliferation markers (PCNA & Ki67) and marker genes of different cell populations in the adrenal gland (e.g., β-catenin, 20αHSD, tyrosine hydroxylase) showed normal zonation and proliferation patterns. The unaffected adrenal glands in Hes1 conditional knockout mice suggests Notch signaling is not a dominant developmental pathway in the adrenal cortex. Next, to study how overactivation of Notch signaling affects adrenocortical cells, we used Sf1-Cre mice to overexpress Notch intracellular domain (NICD) in cortical cells in the adrenal gland. The over-expression of NICD in the adrenal cortex disrupted adrenal cortex zonation and led to a small, disorganized adrenal. These Sf1-Cre mediated NICD over-overexpressed adrenals had scattered and disorganized medulla irregularly distributed in the margin of the gland. Immunostaining showed clusters of 3βHSD low-expressing cells underneath the capsule partially surrounding the 3βHSD high-expressing cortex. Moreover, X-zone cells (labeled by 20αHSD) were significantly reduced in NICD over-overexpressed adrenals in two weeks old male and female mice. Our data suggest that overactivation of Notch signaling in the adrenal cortex not only disrupts the development of the definitive cortical zones but also affects the aging and the differentiation of fetal cortical cells in mice.