Strain-specific differences in levels of the mRNA for the epinephrine synthesizing enzyme phenylethanolamine N-methyltransferase

Association between the phenylethanolamine N-methyltransferase gene and multiple sclerosis

Phenylethanolamine N-methyltransferase (PNMT), the terminal enzyme of the catecholamine biosynthesis pathway, catalyzes the conversion of norepinephrine (NE) to epinephrine (EPI). PNMT is a candidate gene for multiple sclerosis (MS) for two reasons. PNMT is known to map to a region identified in two genome screens for MS and it directly regulates the amounts of NE and EPI, both of which play a significant role in the modulation of the innate immune response. The frequencies of two promoter polymorphisms of the PNMT gene showed genetic association in a case-control study of 108 patients with MS and 774 ethnically and age-matched control subjects. In subjects with MS, significant differences in the frequency of the GG genotype at the G-387A marker and the AA genotype at the G-182A marker were observed. Additionally, when both markers were combined and evaluated, highly significant differences between the polymorphism distributions in patients with MS and control subjects were detected. The data suggest that these promoter polymorphisms of the PNMT gene, both independently and cumulatively, show association with MS.

Glucocorticoids stimulate transcription of the rat phenylethanolamine N-methyltransferase (PNMT) gene in vivo and in vitro

1. Phenylethanolamine N-methyltransferase (PNMT) is regulated by glucocorticoid hormones. This study investigates the ability of glucocorticoids to modulate transcription of the rat PNMT gene in vivo and in vitro. 2. In the adrenal glands of hypophysectomized (HPX'd) rats, the synthetic glucocorticoid dexamethasone (DEX) stimulates production of PNMT mRNA. Quantitative hybridization reveals that the levels of PNMT mRNA increase approximately threefold in total and poly(A)+RNA after 4 days of DEX treatment of HPX'd rats, a level which is maximal for this treatment. 3. ACTH, the hormonal stimulus of glucocorticoid biosynthesis in the adrenal cortex, enhances PNMT mRNA production to levels comparable to that achieved with DEX in this system. The steroid responsiveness of PNMT message production is specific for glucocorticoids. DEX also increases PNMT mRNA in the brain stem, although the magnitude and speed of response are lower than observed in the adrenal gland. 4. Additional confirmation of the inductive ability of glucocorticoids is demonstrated by the increase in PNMT immunoprecipitated following translation in vitro of adrenal RNAs from DEX-treated rats. Furthermore, the PNMT mRNA signal obtained by in situ hybridization histochemistry in adrenal sections and in primary cultures of dispersed rat adrenal medullae reveals that DEX effects on PNMT mRNA can be elicited both in vivo and in vitro. 5. Specifically, glucocorticoids exert their effects on expression of PNMT mRNA by elevating the rate of PNMT gene transcription: a 2.3-fold increase in PNMT transcription persists for 18 hr following DEX treatment of HPX'd rats. In summary, this study establishes that glucocorticoids directly and rapidly stimulate transcription of the rat PNMT gene.

Developmental and strain-specific heterogeneity of rat adrenal chromaffin cells recognized by a monoclonal antibody against intact chromogranin B

We have raised a monoclonal antibody (MAB-1E10) reactive with the intact forms but not the processing products of the chromaffin cell vesicle protein chromogranin B (CgB). The antibody recognizes rat and human, but not bovine and chick adrenal chromaffin cells. In addition, MAB-1E10 immunoreactivity was detected in rat PC 12 pheochromocytoma cells and in pituitaries. Several other tissues, including pancreas, small intestine and superior cervical ganglia, which are known to contain CgB in endocrine cells or neurons, respectively, were found not to be reactive with MAB-1E10. Using short-term cultures of dissociated adrenal chromaffin cells from Hannover-Wistar rats, we found that the expression of intact CgB is developmentally regulated. Between embryonic day 19 and postnatal day 40, about 80% of adrenal chromaffin cells--identified by their reactivity with an antibody against the enzyme dopamine-beta-hydroxylase--were found to be reactive with MAB-1E10. The proportion of positive cells subsequently decreased to about 5% at postnatal day 90. In the presence of glucocorticoids, this decrease was reduced to about 45% CgB-positive cells at postnatal day 90. In another rat strain, Sprague-Dawley rats, the proportion of MAB-1E10-immunoreactive chromaffin cells (about 50%) remained constant from birth to adulthood. Our results indicate that CgB is differentially expressed and/or processed in different rat tissues, strains and during development, and furthermore, that expression or processing in rat chromaffin cells might be regulated by glucocorticoids. Intact CgB appears to be a marker for a subpopulation of chromaffin cells, but its function(s) remains to be clarified.

Strain-specific differences in transcription of the gene for the epinephrine-synthesizing enzyme phenylethanolamine N-methyltransferase

Phenylethanolamine N-methyltransferase (PNMT), the enzyme which synthesizes the catecholamine epinephrine (adrenaline), may be regulated at many levels of expression. This study examines one level, the production of PNMT hnRNA, by measuring its rate of transcription in the rat adrenal gland and bovine adrenal medulla using an in vitro nuclear transcription run-on assay. Furthermore, when the transcriptional rate is compared in strains of rat known to possess distinctive levels of epinephrine and PNMT enzyme, the rate of PNMT transcription in Fischer rats is greater than in Buffalo or Sprague-Dawley rats: relative ratios are 0.54:1.00:1.6 for Buffalo:Sprague-Dawley:Fischer adrenal glands. As such, it appears that the rate of PNMT gene transcription is the major factor responsible for the strain-specific levels of PNMT mRNA among these rats. Therefore, in addition to regulation by neural and steroid influences, an intrinsic genetic component also governs the level of PNMT gene expression.

Possible mechanism of action of SKF 64139 in vivo on rat adrenal and brain phenylethanolamine N-methyltransferase activity

SKF 64139, a specific inhibitor of the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT), has been widely used as a pharmacological tool for studying the characteristics of epinephrine-containing neurons. However, the mechanism of action of this drug on PNMT in vivo has not been fully elucidated. In the present study, we traced changes of PNMT activity in rat adrenal glands and medulla oblongata between 1 and 48 hr after intraperitoneal injection of SKF 64139 (50 mg/kg body wt). Within 1 hr, enzyme activity in both tissues decreased to 10% of the respective control value. However, starting at 4 hr, activity gradually recovered from the inhibition and completely returned to the respective control level by 48 hr. Removal of the inhibitor by dialysis substantially restored the adrenal enzyme activity in 1, 2 and 4 hr groups and completely returned it to control levels in 18 and 48 hr groups. A similar pattern also seemed to hold with brain extracts. The profiles of immunotitration curves, using dialyzed tissue extracts and specific antibodies to bovine adrenal PNMT, clearly indicate that, even after dialysis, a substantial amount of inactive enzyme was present in tissue extracts from 1, 2 and 4 hr groups. In contrast, by 18 hr a very small amount of inactive enzyme was present. Throughout the experimental periods there was no noticeable differences among the control and the experimental groups in the number or intensity of immunocytochemical stained neurons with PNMT antibodies of the C1 area of ventrolateral medulla. Judging from the data obtained by dialysis, immunochemical titration and immunocytochemical staining, recovery of PNMT activity following its inhibition by SKF 64139 was not due to irreversible inhibition of the enzyme followed by new enzyme synthesis. Instead, reversible binding of inhibitor to PNMT and its release were responsible for recovery. PNMT from the 1, 2 and 4 hr groups resisted further in vitro inhibition by SKF 64139 because the residual inhibitor was probably still bound to the enzyme.

Strain differences in distribution of phenylethanolamine N-methyltransferase activity from rat brain and adrenal gland

Phenylethanolamine N-methyltransferase (PNMT) activity was measured in adrenal glands and medulla oblongata from 4 inbred rat strains, Fischer 344, Buffalo, Lewis and Sprague-Dawley rats. Adrenal enzyme activity was markedly different among the strains with the highest in Fischer, followed by Sprague-Dawley, Lewis and Buffalo rats in decreasing order. In medulla oblongata, the PNMT activity of Buffalo rat was the lowest being about one half of that of the other strains. Despite differences in the enzymes activity, immunotitration results indicate that there is no immunochemical difference between adrenal or medulla oblongata PNMT among the strains. Furthermore, the strain differences in the activity are not due to presence of an inactive enzyme, but to the amount of the enzyme. Our preliminary findings by dot blot hybridization, using a 32P-labeled cDNA probe for PNMT suggest that differences in adrenal and medulla oblongata PNMT activity between Fischer and Buffalo rats are partially due to differences in the amount of PNMT mRNA present.