Infusion of ACTH stimulates expression of adrenal ACTH receptor and steroidogenic acute regulatory protein mRNA in fetal sheep

Abstract

-The late-gestation plasma cortisol surge in the sheep fetus is critical for stimulating organ development and parturition. Increased adrenal responsiveness is one of the key reasons for the surge; however, the underlying mechanisms are not fully understood. Our recent studies suggest that ACTH-mediated increased expression of ACTH receptor (ACTH-R) and steroid acute regulatory protein (StAR) may play a role in enhancing responsiveness. Hence, we examined effects of ACTH infusion in fetal sheep on mRNA expression of these two mediators of adrenal responsiveness and assessed the functional consequences of this treatment in vitro. Fetuses of ϳ118 and 138 days of gestational age (dGA) were infused with ACTH-(1-24) for 24 h. Controls received saline infusion. Arterial blood was sampled throughout the infusion. Adrenals were isolated and analyzed for ACTH-R and StAR mRNA, or cells were cultured for 48 h. Cells were stimulated with ACTH, and medium was collected for cortisol measurement. Fetal plasma ACTH and cortisol concentrations increased over the infusion period in both groups. ACTH-R mRNA levels were significantly higher in ACTH-infused fetuses in both the 118 and 138 dGA groups. StAR mRNA increased significantly in both the 118 and 138 dGA groups. Adrenal cells from ACTH-infused fetuses were significantly more responsive to ACTH stimulation in terms of cortisol secretion than those from saline-infused controls. These findings demonstrate that increases in circulating ACTH levels promote increased expression of ACTH-R and StAR mRNA and are coupled to heightened adrenal responsiveness. adrenocorticotropic hormone; ovine fetus IN HUMANS AND MANY MAMMALIAN SPECIES, the late-gestation surge in fetal plasma cortisol levels stimulates final stage development of the lung and other organ systems (7, 22) and indeed, in sheep, initiates birth (19, 32). Parturition occurring before this surge is associated with increased fetal mortality and morbidity, most notably as a consequence of lung immaturity. Whereas the sequence of events leading to cortisol production per se are well understood, the precise mechanisms involved in driving the rise in fetal plasma cortisol in late gestation are yet to be fully explained.It is apparent that important changes take place at each level of the hypothalamic-pituitary adrenal axis, leading to the prepartum increase in fetal plasma cortisol. An intact hypothalamic pituitary connection is essential, as clearly demonstrated by hypothalamic pituitary disconnection (HPD) studies in fetal sheep, in which the major consequences of this disruption are the absence of the cortisol surge (11,34,38,48,53) and delayed parturition (1, 2, 4, 33). Increased adrenal responsiveness also is a critical mediating factor (18,21,41,51). Two important effectors to this end, the adrenocorticotropic hormone receptor (ACTH-R, specifically known as the melanocortin-2 receptor) and steroid acute regulatory protein (StAR), exhibit ontogenic increases in expression that occur in parallel to the cortisol surge (8,17,49)...

ACTH is a potent regulator of gene expression in human adrenal cells

“…In agreement with previous studies (Le Roy et al 2000; Rehman et al 2007; Carey et al 2006; Su et al 2005; Johnston et al 2007; Mountjoy et al 1994), we found that the ACTH receptor-MC2R was significantly stimulated by ACTH incubation (12-fold). We also noticed a significant increase in MRAP mRNA level.…”

“…The acute response is mediated by the activity of the StAR protein, which leads to mobilization of cholesterol from cellular stores to the inner mitochondrial membrane where cholesterol side-chain cleavage (CYP11A1) is located (Fleury et al 1998; Ariyoshi et al 1998; Fleury et al 1996; Clark & Combs 1999; Lehoux et al 2003). Studies in fetal and adult adrenals across several species have shown that the chronic response of ACTH includes the activation of genes encoding the steroidogenic enzymes, HSD3B2, CYP21, CYP17, CYP11B1 (Neri et al 1991; Phillips et al 1996; Simmonds et al 2001; Bassett et al 2004; Schimmer et al 2006; Carey et al 2006; Coulter & Jaffe 1998; Di Blasio et al 1990; Galtier et al 1996; Lebrethon et al 1994; Mason et al 1993; Su et al 2005; Su & Rose 2008; Tangalakis et al 1990; Zhang et al 1999). These gene targets were confirmed in the current study in AA and FA cells using microarray analysis.…”

Gene array and real time PCR analysis of the adrenal sensitivity to adrenocorticotropic hormone in pig

“…The binding of ACTH to its cognate G protein-coupled receptor promotes the activation of protein kinase A and MAPK-dependent signaling cascades that collectively initiate adrenal-specific steroidogenic transcriptional programs [ 21 , 22 , 40 ]. Findings from numerous in vitro studies support the notion that ACTH is a positive regulator of ACTH-R mRNA expression [ 33 , 41 , 42 ]. More particularly, Winnay and Hammer [ 43 ] demonstrated in vitro that ACTH stimulation acutely activates the Mc2r gene promoter (i.e.…”

Designing of peptides with desired half-life in intestine-like environment

“…A large number of peptides like insulin [2], cyclosporine [3], corticotropin [4] are used for treating various diseases like diabetes and immunoregulatory disorders [5–7]. Owing to their immense therapeutic importance, peptides have been curated from literature and stored in form of databases such as Hemolytik [8], PhytAMP [9], APD2 [10], DAMPD [11], CAMP [12], YADAMP [13], CPPsite [14], TumorHoPe [15], Quorumpeps [16], Brainpeps [17], MilkAMP [18], DADP [19], LAMP [20] and AVPdb [21] to name a few.…”