Distribution and regulation of renal mineralocorticoid and glucocorticoid receptor mRNA.

Adrenal corticosteroid hormones play an important role in the maintenance of body fluid and electrolyte balance. In spite of their physiological significance, the specific target sites for adrenal corticosteroid action in the kidney, as well as the mechanisms regulating the expression of the intracellular receptors are still unclear. The first goal was to determine the distribution of mineralocorticoid and glucocorticoid receptor mRNA along the nephron by utilizing a competitive PCR technique. RNA was isolated from microdissected tubules, cDNA synthesized and co-amplified together with a competitive control template. $\beta$-Actin product from each nephron segment was used to assess variations in RNA purification and cDNA synthesis. Mineralocorticoid receptor mRNA, was ten fold more abundant in cortical collecting ducts (CCD), outer medullary collecting ducts, and inner medullary collecting ducts, than in glomeruli, proximal convoluted tubules, proximal straight tubules (PST), medullary thick ascending limbs and cortical thick ascending limbs (p $<$ 0.05). Glucocorticoid receptor mRNA was twice as abundant in glomeruli, proximal tubules and thick ascending limbs, than in the collecting duct segments (p $<$ 0.05). Largely consistent with functional studies, these results suggest that collecting duct cells predominantly express mineralocorticoid receptors, whereas glomeruli, proximal tubules and thick ascending limbs are the predominant glucocorticoid receptor containing segments. The second goal was to determine if altered plasma concentrations of adrenal corticosteroids affect renal mineralocorticoid and glucocorticoid receptor mRNA levels in parallel with the changes known to occur in renal receptor levels. Scatchard analysis revealed that aldosterone binding sites in rat kidney cytosol increased three fold following adrenalectomy. Mineralocorticoid and glucocorticoid receptor mRNA levels in kidney cortex and medulla, measured by dot blot hybridization, were not significantly different between control, adrenalectomized, and DOCA or dexamethasone replaced rats. Furthermore, adrenalectomy did not significantly alter mineralocorticoid and glucocorticoid receptor mRNA levels in microdissected PST or CCD as assessed by competitive PCR. Thus, regulation of mineralocorticoid and glucocorticoid receptor numbers in response to altered corticosteroid plasma concentrations appears to be mediated by a post-transcriptional mechanism.Ph.D.PhysiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103324/1/9308467.pdfDescription of 9308467.pdf : Restricted to UM users only

Expression and Distribution of Cystic Fibrosis Transmembrane Conductance Regulator in Neurons of the Human Brain

The importance of the molecule cystic fibrosis transmembrane conductance regulator (CFTR) is reflected in the many physiological functions it regulates. It is known to be present in epithelial cells of the lungs, pancreas, sweat glands, gut, and other tissues, and gene mutations of CFTR cause cystic fibrosis (CF). We studied the expression and distribution of CFTR in the human brain with reverse transcriptase polymerase chain reaction, in situ hybridization, and immunohistochemistry. This study demonstrates widespread and abundant expression of CFTR in neurons of the human brain. Techniques of double labeling and evaluation of consecutive tissue sections localized CFTR protein and mRNA signals to the cytoplasm of neurons in all regions of the brain studied, but not to glial cells. The presence of CFTR in central neurons not only provides a possible explanation for the neural symptoms observed in CF patients, but also may lead to a better understanding of the functions of CFTR in the human brain. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials. (J Histochem Cytochem 57:1113–1120, 2009