Remodeling of Turkey Adrenal Steroidogenic Tissue Induced by Dietary Protein Restriction: The Potential Role of Cell Death

Abstract

The present study focused on the cellular remodeling of steroidogenic tissue in the domestic turkey (Meleagris gallopavo) adrenal gland in response to dietary protein restriction stress. Immature male turkeys (1 week old) were fed isocaloric synthetic diets containing either 28% (control) or 8% (restriction) soy protein for 4 weeks. Adrenal glands were processed for the isolation of density- separable, visibly distinct adrenal steroidogenic cell subpopulations: three low-density subpopulations [LDAC-1 (ρ = 1.0350–1.0490 g/ml), LDAC-2 (ρ = 1.0490–1.0570 g/ml), and LDAC-3 (ρ = 1.0570–1.0585 g/ml)] and one high-density subpopulation [HDAC (ρ = 1.0590–1.0720 g/ml)]. Dietary protein restriction increased the proportion of LDAC-3 and HDAC by 98 and 350%, respectively, and decreased LDAC-2 by 46%. LDAC-1 also showed signs of proportional decrement. To determine the role of cell death in this process, the potential for apoptosis was assessed in adrenal tissue and isolated adrenal steroidogenic cells using short-term culture followed by analysis of oligonucleosome formation. Basal, culture-triggered oligonucleosome formation of tissue and cells derived from protein-restricted birds was 80% greater than that of tissue and cells derived from control birds. This differential in apoptotic potential persisted with a variety of treatments, in vitro. Apoptotic potential was suppressed by human adrenocorticotropin and enhanced by angiotensin II (Ang II). The proapoptotic effect of Ang II (100 nM) with adrenal fragments was inhibited by the Ang II receptor antagonist [Sar1, Ile8]ang II (10 μM) to below basal values (by about 60%), but the inhibition was surmountable by high concentrations (10 and 100 μM) of Ang II. The antagonist also attenuated basal, culture-triggered DNA fragmentation of tissue and cells, suggesting that at least part of the basal DNA fragmentation was due to intrinsically generated Ang II. Differences in apoptotic potential were also apparent with cell subpopulations. Compared to control subpopulations, protein restriction enhanced basal oligonucleosome formation in LDAC-1 and -2 by 38 and 122%, respectively, and reduced it in LDAC-3 and HDAC by 53 and 70%, respectively. These data suggest a role for apoptotic cell death in the remodeling of turkey adrenal steroidogenic tissue induced by dietary protein restriction. In addition, other data suggest that Ang II is an important regulator of adrenal steroidogenic cell turnover in the avian adrenal gland.