A role for picomolar concentrations of pregnenolone sulfate in synaptic activity-dependent Ca2+ signaling and CREB activation.

Fast excitatory synaptic transmission that is contingent upon N-methyl d-aspartate receptor (NMDAR) function contributes to core information flow in the central nervous system and to the plasticity of neural circuits that underlie cognition. Hypoactivity of excitatory NMDAR-mediated neurotransmission is hypothesized to underlie the pathophysiology of schizophrenia, including the associated cognitive deficits. The neurosteroid pregnenolone (PREG) and its metabolites pregnenolone sulfate (PregS) and allopregnanolone in serum are inversely associated with cognitive improvements after oral PREG therapy, raising the possibility that brain neurosteroid levels may be modulated therapeutically. PregS is derived from PREG, the precursor of all neurosteroids, via a single sulfation step and is present at low nanomolar concentrations in the central nervous system. PregS, but not PREG, augments long-term potentiation and cognitive performance in animal models of learning and memory. In this report, we communicate the first observation that PregS, but not PREG, is a potent (EC50 ∼2 pM) enhancer of intracellular Ca(2+) that is contingent upon neuronal activity, NMDAR-mediated synaptic activity, and L-type Ca(2+) channel activity. Low picomolar PregS similarly activates cAMP response element-binding protein (CREB) phosphorylation (within 10 minutes), an essential memory molecule, via an extracellular-signal-regulated kinase/mitogen-activated protein kinase signal transduction pathway. Taken together, the results are consistent with a novel biologic role for the neurosteroid PregS that acts at picomolar concentrations to intensify the intracellular response to glutamatergic signaling at synaptic but not extrasynaptic, NMDARs by differentially augmenting CREB activation. This provides a genomic signal transduction mechanism by which PregS could participate in memory consolidation of relevance to cognitive function.

Pregnenolone sulfate as a modulator of synaptic plasticity.

RATIONALE: The neurosteroid pregnenolone sulfate (PregS) acts as a cognitive enhancer and modulator of neurotransmission, yet aligning its pharmacological and physiological effects with reliable measurements of endogenous local concentrations and pharmacological and therapeutic targets has remained elusive for over 20 years. OBJECTIVES: New basic and clinical research concerning neurosteroid modulation of the central nervous system (CNS) function has emerged over the past 5 years, including important data involving pregnenolone and various neurosteroid precursors of PregS that point to a need for a critical status update. RESULTS: Highly specific actions of PregS affecting excitatory N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic transmission and the pharmacological effects of PregS on various receptors and ion channels are discussed. The discovery of a high potency (nanomolar) signal transduction pathway for PregS-induced NMDAR trafficking to the cell surface via a Ca(2+)- and G protein-coupled receptor (GPCR)-dependent mechanism and a potent (EC50 ~ 2 pM) direct enhancement of intracellular Ca(2+) levels is discussed in terms of its agonist effects on long-term potentiation (LTP) and memory. Lastly, preclinical and clinical studies assessing the promnestic effects of PregS and pregnenolone toward cognitive dysfunction in schizophrenia, and altered serum levels in epilepsy and alcohol dependence, are reviewed. CONCLUSIONS: PregS is present in human and rodent brain at physiologically relevant concentrations and meets most of the criteria for an endogenous neurotransmitter/neuromodulator. PregS likely plays a significant role in modulation of glutamatergic excitatory synaptic transmission underlying learning and memory, yet the molecular target(s) for its action awaits identification.

Synthesis and biological properties of the fluorescent ether lipid precursor 1-O-[9'-(1''-pyrenyl)]nonyl-sn-glycerol.

The synthesis of an omega-pyrene-labeled 1-O-alkyl-sn-glycerol was performed using a chirospecific method starting from R-(-)-2,3-O-isopropylidene-sn-glycerol. The product, 1-O-[9'-(1''-pyrenyl)]nonyl-sn-glycerol (pAG), is a fluorescent ether lipid that has a pyrene moiety covalently attached at the alkyl chain terminus. pAG was taken into CHO-K1 cells and a plasmalogen-deficient variant of CHO-K1, NRel-4. This variant is defective in dihydroxyacetonephosphate acyltransferase, which catalyzes the first step in plasmenylethanolamine (PlsEtn) biosynthesis. pAG was incorporated primarily into ethanolamine and choline phospholipids as well as a neutral lipid fraction tentatively identified as alkyldiacylglycerol. NRel-4 accumulated more fluorescence in the phospholipid fraction than CHO-K1, specifically in the ethanolamine phospholipids. Analysis of the fluorescent lipids showed that 93% of the pAG was incorporated into glycerolipids with the ether bond intact. Although the addition of 20 microM 1-O-hexadecyl-sn-glycerol to the medium fully restored PlsEtn biosynthesis in NRel-4 cells, pAG only partially restored PlsEtn synthesis. Incubation of cells with pAG followed by irradiation with long-wavelength (>300 nm) ultraviolet light resulted in cytotoxicity. NRel-4 cells displayed an increased sensitivity to this treatment compared with CHO-K1 cells. This photodynamic cytotoxicity approach could be used to select for mutants that are defective in downstream steps in ether lipid biosynthesis.