Control of Steroid 21-oic Acid Synthesis by Peroxisome Proliferator-activated Receptor α and Role of the Hypothalamic-Pituitary-Adrenal Axis

Ting Wang,Yatrik M Shah,Tsutomu Matsubara,Yueying Zhen,Tomotaka Tanabe,Tomokazu Nagano,Serge Fotso,Kristopher W Krausz,T Mark Zabriskie,Jeffrey R Idle,Frank J Gonzalez

doi:10.1074/jbc.m109.090175

Abstract

A previous study identified the peroxisome proliferator-activated receptor alpha (PPARalpha) activation biomarkers 21-steroid carboxylic acids 11beta-hydroxy-3,20-dioxopregn-4-en-21-oic acid (HDOPA) and 11beta,20-dihydroxy-3-oxo-pregn-4-en-21-oic acid (DHOPA). In the present study, the molecular mechanism and the metabolic pathway of their production were determined. The PPARalpha-specific time-dependent increases in HDOPA and 20alpha-DHOPA paralleled the development of adrenal cortex hyperplasia, hypercortisolism, and spleen atrophy, which was attenuated in adrenalectomized mice. Wy-14,643 activation of PPARalpha induced hepatic FGF21, which caused increased neuropeptide Y and agouti-related protein mRNAs in the hypothalamus, stimulation of the agouti-related protein/neuropeptide Y neurons, and activation of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in increased adrenal cortex hyperplasia and corticosterone production, revealing a link between PPARalpha and the HPA axis in controlling energy homeostasis and immune regulation. Corticosterone was demonstrated as the precursor of 21-carboxylic acids both in vivo and in vitro. Under PPARalpha activation, the classic reductive metabolic pathway of corticosterone was suppressed, whereas an alternative oxidative pathway was uncovered that leads to the sequential oxidation on carbon 21 resulting in HDOPA. The latter was then reduced to the end product 20alpha-DHOPA. Hepatic cytochromes P450, aldehyde dehydrogenase (ALDH3A2), and 21-hydroxysteroid dehydrogenase (AKR1C18) were found to be involved in this pathway. Activation of PPARalpha resulted in the induction of Aldh3a2 and Akr1c18, both of which were confirmed as target genes through introduction of promoter luciferase reporter constructs into mouse livers in vivo. This study underscores the power of mass spectrometry-based metabolomics combined with genomic and physiologic analyses in identifying downstream metabolic biomarkers and the corresponding upstream molecular mechanisms.

Highlights

The mechanisms of biomarker (HDOPA and 20␣-dihydroxy-3-oxo-pregn-4-en-21-oic acid (DHOPA)) synthesis under PPAR␣ activation were identified as first the PPAR␣-stimulated adrenal cortex hyperplasia and associated hypercortisolism that provide high levels of precursor corticosterone, and second, the PPAR␣-induced alternative oxidative pathway that metabolizes corticosterone to 21-carboxylic acids
With increased or pharmacological levels of corticosteroids, for example, the hypercortisolism status under WY administration as observed in this study, a larger fraction of nonprotein-bound steroid is available for diffusion into the extravascular spaces and in coordination with the oxidases induced by PPAR␣, corticosterone is converted to the carboxylic acids as a major metabolic pathway
The subsequent conversion of HDOPA to 20␣-DHOPA [IV], a simple C20-ketone reduction, is suppressed in response to the accumulating oxidative stress triggered by PPAR␣ activation, which explains the relatively lower specificity of 20␣-DHOPA to PPAR␣ activation compared with the oxidative product HDOPA, including levels in urine and tissue, patterns of time-dependent induction, responses to WY withdrawal, and profiles of metabolite production

Summary

Introduction

Activation of the HPA Axis by PPAR␣ Ligands and the Attenuation of HDOPA and 20␣-DHOPA Production by Adrenalectomy—During WY administration, the increases in urinary HDOPA and 20␣-DHOPA were associated with elevated adrenal weights (Fig. 2A) and circulating serum corticosterone levels (Fig. 2B) compared with the control-fed mice. Ever, unexpectedly, the activity of WY-fed liver homogenates in the metabolism of HDOPA to 20␣-DHOPA was significantly lower compared with the control homogenates, the rates of 20␣-DHOPA production were relatively lower but with no significance while using corticosterone and 21-gem-diol as the substrates (Fig. 5C).

Results

Conclusion