Elsevier

Journal of Psychiatric Research

Volume 60, January 2015, Pages 40-48
Journal of Psychiatric Research

Distinct proteomic profiles in post-mortem pituitary glands from bipolar disorder and major depressive disorder patients

https://doi.org/10.1016/j.jpsychires.2014.09.022Get rights and content

Highlights

  • Pituitary disturbances have been implicated in psychiatric disorders.

  • This proteomic study identified differences in pituitaries from BD and MDD patients.

  • BD patients had changes mainly in hormones, growth factors and metabolism.

  • MDD patients had changes in prohormone converting enzymes and cell structure proteins.

  • Many of these proteins could be focal points in the search for peripheral biomarkers.

Abstract

Disturbances of the hypothalamic–pituitary–adrenal axis have been implicated in the pathophysiology of bipolar disorder (BD) and major depressive disorder (MDD). To examine this further, we carried out proteomic profiling of post-mortem pituitaries from 13 BD and 14 MDD patients, in comparison to 15 controls. Liquid chromatography–mass spectrometry (LC–MSE) analysis showed that BD patients had significantly increased levels of the major pituitary hormones pro-opiomelanocortin (POMC) and galanin. BD patients also showed changes in proteins associated with gene transcription, stress response, lipid metabolism and growth signalling. In contrast, LC–MSE profiling revealed that MDD patients had significantly decreased levels of the prohormone-converting enzyme carboxypeptidease E and follow-up enzymatic analysis showed decreased activity of prolyl-oligopeptidase convertase. This suggested that altered prohormone processing may occur in pituitaries of MDD patients. In addition, MDD patients had significant changes in proteins involved in intracellular transport and cytoskeletal signalling. Finally, we carried out selective reaction monitoring (SRM) mass spectrometry profiling for validation of protein changes in key biological pathways. This confirmed increased POMC levels in BD patients with no change in the levels of this prohormone in MDD. This study demonstrates that proteomic profiling analysis of the pituitary can lead to new insights into the pathophysiology of BD and MDD. Also, given that the pituitary directly releases a variety of bioactive molecules into the bloodstream, many of the proteins identified here could serve as focal points in the search for peripheral biomarkers in clinical or drug treatment studies of BD and MDD patients.

Introduction

Bipolar disorder (BD) and major depressive disorder (MDD) have a lifetime prevalence of 20% (Hirschfeld, 2012). Individuals with either of these disorders have decreased life expectancies due to suicide and increased comorbidities such as obesity, diabetes, dyslipidemia and cardiac disease (Ferrari et al., 2013, Hauser et al., 2013). Some of these co-morbidities can be side effects from psychiatric medications (Gazalle et al., 2007, McLaren and Marangell, 2004). Also, misdiagnosis or inappropriate treatment can have negative effects on health and result in a worse outcome for patients (Bowden, 2010). Recent studies have attempted to increase our understanding of the underlying pathophysiologies of BD and MDD through identification of disease-specific biomarkers (Alsaif et al., 2013, Schneider and Prvulovic, 2013). These studies have identified hypothalamic–pituitary–adrenal (HPA) axis perturbations in many patients with mood disorders (Banki et al., 1987, Grunze, 2011, Tsigos and Chrousos, 2002). The HPA axis is a component of the diffuse neuroendocrine system involved in regulation of vital homoeostatic systems throughout the body, including blood pressure, metabolism, inflammation and fluid balance. Effects on all of these processes have been implicated in BD and MDD. In addition, pituitary size is known to be enlarged in adolescents with BD and MDD, indicating that hormonal abnormalities may occur at early stages of disease (MacMaster et al., 2008). One of the most studied components of the HPA axis is regulation of the stress response via proteolytic conversion of pro-opiomelanocortin (POMC) to adrenocorticotropin (ACTH) in the anterior pituitary (Arlt and Stewart, 2005). Secretion of ACTH into the peripheral circulation stimulates release of cortisol from the adrenal cortex, which in turn can affect brain function (Frodl and O'Keane, 2013). Under normal circumstances, cortisol also acts on the hypothalamus and pituitary in a negative feedback loop to suppress production of ACTH.

Several other proteins produced by the pituitary have effects on the brain. For example, galanin regulates cognition, neuronal growth and neuronal protection (Mechenthaler, 2008). Growth hormone (somatotropin) has been implicated in several pathways including the sleep–wake cycle, brain development and neuronal repair (Arce et al., 2013). Prolactin is involved in diverse processes such as regulation of the immune response, neurogenesis and neuronal differentiation (Larsen and Grattan, 2012). Also, the production of prolactin is tightly regulated with that of neurotransmitters such as dopamine which can affect behaviour and mood (van den Pol, 2010). The pituitary also contains prohormone-converting enzymes such as carboxypeptidase E (CPE) and prolyl-oligopeptidase 1 (POP), which are involved in proteolytic maturation of pituitary hormones and other proproteins, leading to generation of a spectrum of bioactive peptides (Hook et al., 2009, Yoshimoto et al., 1981).

The aim of this study was to identify HPA axis biomarker candidates for BD and MDD using post-mortem pituitary tissue. Protein extracts were analysed using a combination of liquid chromatography mass spectrometry (LC–MSE), selective reaction-monitoring (SRM) mass spectrometry and an enzyme assay to identify BD- and MDD-associated proteomic fingerprints. The analyses focussed on identification of secreted pituitary proteins as these could be translated into blood-based assays for future clinical studies.

Section snippets

Samples

Whole post-mortem pituitaries from 15 control, 13 BD and 14 MDD subjects were provided by the Stanley Medical Research Institute (Bethesda, MD, USA). These were matched for variables including age at death, gender, post-mortem brain interval (PMI), duration of storage, onset age, duration of illness, death by suicide and history of substance abuse (Table 1). The control subjects had no history of psychiatric or neurological disorders. Tissue had been collected post-mortem with informed consent

LC–MSE profiling

Demographic variables that were significantly different between the groups were duration of storage and illness, age of onset and death by suicide (Table 1). LC–MSE analysis of soluble and insoluble pituitary extracts from control, BD and MDD subjects resulted in identification of 796 (Supplementary Table 1) and 863 (Supplementary Table 2) proteins, respectively (Supplementary Fig. 1). This translated to 1224 unique identifications with 435 proteins overlapping between the two fractions. All

Discussion

This is the first LC–MSE profiling analysis of post-mortem pituitary tissues comparing two major psychiatric disorders. The analysis revealed differences in proteins and molecular pathways between BD and MDD patients. BD patients showed significantly increased levels of the hormones POMC and galanin. The additional finding that the levels of these hormones were significantly correlated is consistent with reports that galanin stimulates activity of the POMC-derived peptide ACTH (Malendowicz

Ethical approval statement

All subjects gave informed written consent. Clinical investigations were conducted according to the Declaration of Helsinki, and the University of Cambridge ethical committee approved the study.

Role of funding source

This work was supported by the Stanley Medical Research Institute (SMRI) (07R-1888), the Dutch Fund for Economic Structure Reinforcement (FES), under grant agreement number 0908 (NeuroBasic PharmaPhenomics project) and the European Union FP7 SchizDX research programme (grant reference 223427). The funding sources had no further role in: the study design; in the collection, analysis and interpretation of the data; in the report writing; and in the decision to submit the paper for publication.

Author's contributions

V. Stelzhammer and M. Alsaif analysed the samples and wrote the Manuscript. H. Steeb analysed the samples. H. Rahmoune, P.C. Guest and S. Bahn designed the study and edited the manuscript. Man K. Chan analysed the data and edited the manuscript. All authors reviewed and approved the article.

Statement of interest

Sabine Bahn has consulted for Myriad Genetics Inc. This does not interfere with the policies of the journal regarding sharing or ownership of data and materials. All other authors do not report any conflicts of interest. Appropriate approval and procedures were used concerning subjects.

Acknowledgements

This research was supported by the Stanley Medical Research Institute (SMRI), the European Union FP7 SchizDX research programme (grant reference 223427) and the NeuroBasic grant from the Dutch government. We also thank Dr. Jason D. Cooper for his statistical advice, the SMRI for the generous donation of post-mortem pituitaries and Maree Webster for useful discussion.

References (53)

  • C.M. Larsen et al.

    Prolactin, neurogenesis, and maternal behaviors

    Brain Behav Immun

    (2012)
  • M. Maes et al.

    Alterations in plasma prolyl endopeptidase activity in depression, mania, and schizophrenia: effects of antidepressants, mood stabilizers, and antipsychotic drugs

    Psychiatry Res

    (1995)
  • A. Mazarati et al.

    Patterns of seizures, hippocampal injury and neurogenesis in three models of status epilepticus in galanin receptor type 1 (GalR1) knockout mice

    Neuroscience

    (2004)
  • M.C. Pepin et al.

    Antidepressants regulate glucocorticoid receptor messenger RNA concentrations in primary neuronal cultures

    Brain Res Mol Brain Res

    (1989)
  • C.J. Phiel et al.

    Histone deacetylase is a direct target of valproic acid, a potent anticonvulsant, mood stabilizer, and teratogen

    J Biol Chem

    (2001)
  • C. Piubelli et al.

    Regulation of cytoskeleton machinery, neurogenesis and energy metabolism pathways in a rat gene-environment model of depression revealed by proteomic analysis

    Neuroscience

    (2011)
  • C. Tsigos et al.

    Hypothalamic-pituitary-adrenal axis, neuroendocrine factors and stress

    J Psychosom Res

    (2002)
  • L.L. Valiengo et al.

    Plasma cortisol in first episode drug-naive mania: differential levels in euphoric versus irritable mood

    J Affect Disord

    (2012)
  • A.N. van den Pol

    Excitatory neuromodulator reduces dopamine release, enhancing prolactin secretion

    Neuron

    (2010)
  • S. Watson et al.

    Lithium, arginine vasopressin and the dex/CRH test in mood disordered patients

    Psychoneuroendocrinology

    (2007)
  • M. Alsaif et al.

    Challenges in drug target discovery in bipolar disorder

    Expert Opin Ther Targets

    (2013)
  • C.M. Banki et al.

    CSF corticotropin-releasing factor-like immunoreactivity in depression and schizophrenia

    Am J Psychiatry

    (1987)
  • Y. Benjamini et al.

    Controlling the false discovery rate: a practical and powerful approach to multiple testing

    J R Stat Soc Ser B Methodol

    (1995)
  • G.S. Bennett et al.

    Expression and phosphorylation of the mid-sized neurofilament protein NF-M during chick spinal cord neurogenesis

    J Neurosci Res

    (1988)
  • C.L. Bowden

    Diagnosis, treatment, and recovery maintenance in bipolar depression

    J Clin Psychiatry

    (2010)
  • W.T. Carpenter et al.

    Cortisol's effects on human mental functioning

    J Clin Psychopharmacol

    (1982)
  • Cited by (0)

    1

    These authors contributed equally.

    2

    Tel.: +44 1223767799.

    3

    Tel.: +44 1223746687.

    View full text