Possible role of pineal allopregnanolone in Purkinje cell survival

Abstract

It is believed that neurosteroids are produced in the brain and other nervous systems. Here, we show that allopregnanolone (ALLO), a neurosteroid, is exceedingly produced in the pineal gland compared with the brain and that pineal ALLO acts on the Purkinje cell, a principal cerebellar neuron, to prevent apoptosis in the juvenile quail. We first demonstrated that the pineal gland is a major organ of neurosteroidogenesis. A series of experiments using molecular and biochemical techniques has further demonstrated that the pineal gland produces a variety of neurosteroids de novo from cholesterol in the juvenile quail. Importantly, ALLO was far more actively produced in the pineal gland than in the brain. Pinealectomy (Px) decreased ALLO concentration in the cerebellum and induced apoptosis of Purkinje cells, whereas administration of ALLO to Px quail chicks prevented apoptosis of Purkinje cells. We further found that Px significantly increased the number of Purkinje cells that expressed active caspase-3, a key protease in apoptotic pathway, and daily injection of ALLO to Px quail chicks decreased the number of Purkinje cells expressing active caspase-3. These results indicate that the neuroprotective effect of pineal ALLO is associated with the decrease in caspase-3 activity during the early stage of neuronal development. We thus provide evidence that the pineal gland is an important neurosteroidogenic organ and that pineal ALLO may be involved in Purkinje cell survival during development. This is an important function of the pineal gland in the formation of neuronal circuits in the developing cerebellum.steroid | melatonin | HPLC | gas chromatography/mass spectrometry T he cerebellar cortex has been used as an excellent model to study synaptic formation and transmission of neural networks because it forms relatively simple neuronal networks compared with those of other brain regions. The Purkinje cell is a principal cerebellar neuron that integrates the process of memory and learning. It is known that in birds and mammals pinealectomy (Px) induces cell loss in the brain including Purkinje cells during development (1, 2). This observation suggests that a certain component(s) in the pineal gland contributes to Purkinje cell survival during development.It is now established that steroids can be synthesized de novo in the central and peripheral nervous systems. Such steroids are called "neurosteroids," and de novo neurosteroidogenesis from cholesterol is a conserved property of the vertebrate brain (for reviews, see refs. 3-7). The Purkinje cell is known as a site of neurosteroidogenesis in the brain (for review, see ref. 8). This cerebellar neuron produces progesterone (PROG) and estradiol-17β (E2) de novo from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both PROG and E2 promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell (9-11). Allopregnanolone (ALLO; 3α,5α-tetrahydroprogesterone), a progesterone metabol...

Biosynthesis and Biological Actions of Pineal Neurosteroids in Domestic Birds

“…Therefore, the demonstration of pregnenolone formation from cholesterol is essential to establish de novo neurosteroidogenesis in the pineal gland. As an initial step in the demonstration of pregnenolone biosynthesis in the pineal gland, we found that cytochrome P450scc is expressed in the pineal gland of juvenile chickens [52] and juvenile quail [53] by reverse transcription polymerase chain reaction (RT-PCR) analysis (fig. 1).…”

“…However, recent studies carried out in chickens [52] and quail [53] have demonstrated that the pineal gland, an endocrine organ located close to the brain, actively synthesizes neurosteroids de novo from cholesterol via pregnenolone (fig. 1).…”

“…Immunohistochemical labeling with cytochrome P450scc antibodies showed intense staining in cells forming follicular structures in the quail pineal gland [53]. Incubation of the pineal glands from quail chicks with tritiated cholesterol led to the formation of a radioactive metabolite that, upon high-performance liquid chromatography (HPLC) analysis, exhibited the same retention time as pregnenolone [53]. The occurrence of pregnenolone in the pineal gland was also demonstrated by gas chromatography-mass spectrometry (GC-MS) analysis [53].…”

“…Importantly, the pineal gland produces 7α-hydroxypregnenolone stimulating locomotor activity in light- and circadian time-dependent manners [52]. On the other hand, allopregnanolone produced in the pineal gland prevents cell death of Purkinje cells by suppressing the activity of caspase-3 in the cerebellum during development [53]. Based on these new findings, this review highlights the biosynthesis and biological actions of pineal neurosteroids.…”

“…However, there is now new evidence that, in the juvenile birds, the pineal gland, an endocrine organ located close to the brain, actively produces a variety of neurosteroids de novo from cholesterol [52,53]. Notably, 7α-hydroxypregnenolone and allopregnanolone (3α,5α-tetrahydroprogesterone; 3α,5α-THP) are major neurosteroids secreted by the pineal gland [52,53]. Importantly, the pineal gland produces 7α-hydroxypregnenolone stimulating locomotor activity in light- and circadian time-dependent manners [52].…”