Microarray Analysis Reveals Interleukin-6 as a Novel Secretory Product of the Hypothalamo-neurohypophyseal System

Abstract

Physiological activation of the hypothalamo-neurohypophyseal system (HNS) by dehydration results is a massive release of vasopressin (VP) from the posterior pituitary. This is accompanied by a functional remodeling of the HNS. In this study we used cDNA arrays in an attempt to identify genes that exhibit differential expression in the hypothalamus following dehydration. Our study revealed nine candidate genes, including interleukin-6 (IL-6) as a putative novel secretory product of HNS worthy of further analysis. In situ hybridization and immunocytochemistry confirmed that IL-6 is robustly expressed in the supraoptic (SON) and the paraventricular (PVN) nuclei of the hypothalamus. By doublestaining immunofluorescence we showed that IL-6 is largely co-localized with VP in the SON and PVN. In situ hybridization, immunocytochemistry, and Western blotting all revealed IL-6 up-regulation in the SON and PVN following dehydration, thus validating the array data. The same dehydration stimulus resulted in an increase in IL-6 immunoreactivity in the axons of the internal zone of the median eminence and a marked reduction in IL-6-like material in the posterior pituitary gland. We thus suggest that IL-6 takes the same secretory pathway as VP and is secreted from the posterior pituitary following a physiological stimulus.The hypothalamo-neurohypophyseal system (HNS) 1 consists of large magnocellular neurons (MCNs) of the supraoptic (SON) and paraventricular (PVN) hypothalamic nuclei that have axons terminating on blood capillaries of the posterior pituitary (1), along with associated glia, blood vessels, interneurons, and afferent terminals. The HNS is the source of the neuropeptide hormone vasopressin (VP), which has a crucial role in osmoregulation (2). Following the onset of an osmotic stimulus such as dehydration (fluid deprivation), mammals respond to plasma hyperosmolality by reducing the renal excretion of water. Tubular reabsorption of water is controlled by circulating levels of VP. A rise in plasma osmolality is detected by osmoreceptor mechanisms in the circumventricular organs (3-6). Subsequent angiotensinergic (7,8) and glutamatergic (9 -11) excitation of hypothalamic neurons leads to a massive release of stored VP into the general circulation. Through an interaction with V2-type receptors located in the kidney, VP increases the permeability of the collecting ducts to water, promoting water conservation by decreasing the amount of water lost in urine.Physiological activation of the MCNs by dehydration results in a massive release of stored hormone from posterior pituitary terminals, and a concomitant functional remodeling of the HNS, characterized by activity-dependent secretory, electrophysiological, biosynthetic, and gene expression plasticity (12)(13)(14). At the morphological level, this plasticity is manifested as synaptic remodeling, increased direct neuronal membrane apposition and dendritic bundling in the SON, and by changes in the organization of neurovascular contacts in the neurohypophysis (12). For ex...

A comprehensive description of the transcriptome of the hypothalamoneurohypophyseal system in euhydrated and dehydrated rats

“…The availability of genome information and the parallel development of transcriptomic (microarray) technologies have provided the means to answer two crucial questions: (i) what genes are expressed in the different compo-nents of the NHS, namely the PVN, the SON and the neurointermediate lobe (NIL) of the pituitary gland and (ii) what genes are up-or down-regulated in these same structures after dehydration? Thus, a number of groups have started to use microarray global gene expression profiling technologies to address the question of how many of these genes are utilized by the SON (23) and how the overall pattern of gene expression is changed in the SON by osmotic cues (24,25). The physiological value of this approach has been illustrated by our recent identification of IL-6 as a secretory product of the HNS (24).…”

“…Thus, a number of groups have started to use microarray global gene expression profiling technologies to address the question of how many of these genes are utilized by the SON (23) and how the overall pattern of gene expression is changed in the SON by osmotic cues (24,25). The physiological value of this approach has been illustrated by our recent identification of IL-6 as a secretory product of the HNS (24).…”

Negative correlation of Nogo-A with the malignancy of oligodendroglial tumor

“…Immunohistochemistry was done as previously described [15] . Briefly, samples were cut into sections at 30-50 µm on a vibrating microtome.…”

Selective Gene Expression in Magnocellular Neurons in Rat Supraoptic Nucleus

“…A recent microarray study of the SON (Ghorbel et al, 2003) used a functional criterion (i.e., changes in gene expression with chronic dehydration) to identify potentially interesting genes expressed in the SON. Using a hand-dissection of the SON and an array assay of 1152 gene sequences, they identified 9 genes that were regulated by dehydration.…”