Progesterone (P4) and estradiol (E2) modulate neurogenesis and synaptic remodeling in the hippocampus during the rat estrous cycle and in response to deafferenting lesions, but little is known about the steroidal regulation of hippocampal progesterone receptors associated with these processes. We examined the neuronal expression of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr), by in situ hybridization and immunohistochemistry. Pgr, a transcription factor, has been associated with synaptic remodeling and other major actions of P4, whereas Pgrmc1 is implicated in P4-dependent proliferation of adult neuroprogenitor cells and with rapid P4 effects on membranes. Ovariectomized adult rats were given E2, P4, or E2+P4 on two schedules: a 4-d model of the rodent estrous cycle and a 30-d model of postmenopausal hormone therapy. Pgr was hormonally responsive only in CA1 pyramidal neurons, and the induction of Pgr by E2 was partly antagonized by P4 only on the 30-d schedule. In CA3 pyramidal and dentate gyrus (DG) neurons, Pgr was largely unresponsive to all hormone treatments. In contrast to Pgr, Pgrmc1 was generally induced by E2 and/or P4 throughout the hippocampus in CA1, CA3, and DG neurons. In neuroprogenitor cells of the DG (immunopositive for bromodeoxyuridine and doublecortin), both Pgrmc1 and Pgr were detected. The differential regulation of hippocampal Pgrmc1 and Pgr by E2 and P4 may guide drug development in hormonal therapy for support of neurogenesis and synaptic regeneration.

The monoamine oxidase isoenzymes (MAOs) A and B play important roles in the homeostasis of monoaminergic neurotransmitters. The combined deficiency of MAO A and B results in significantly elevated levels of serotonin (5-hydroxytryptamine), norepinephrine, dopamine, and β-phenylethylamine; in humans and mice, these neurochemical changes are accompanied by neurodevelopmental perturbations as well as autistic-like responses. Ample evidence indicates that normal levels of monoamines in the hippocampus, amygdala, frontal cortex, and cerebellum are required for the integrity of learning and memory. Thus, in the present study, the cognitive status of MAO A/B knockout (KO) mice was examined with a wide array of behavioral tests. In comparison with male wild-type littermates, MAO A/B KO mice exhibited abnormally high and overgeneralized fear conditioning and enhanced eye-blink conditioning. These alterations were accompanied by significant increases in hippocampal long-term potentiation and alterations in the relative expression of NMDA glutamate receptor subunits. Our data suggest that chronic elevations of monoamines, because of the absence of MAO A and MAO B, cause functional alterations that are accompanied with changes in the cellular mechanisms underlying learning and memory. The characteristics exhibited by MAO A/B KO mice highlight the potential of these animals as a useful tool to provide further insight into the molecular bases of disorders associated with abnormal monoaminergic profiles.adult neurogenesis | autism-spectrum disorder | cognition M onoaminergic neurotransmitters, such as serotonin (5-HT), norepinephrine (NE), and dopamine (DA), are known to play a critical role in the modulation of mood and emotion, as well as the control of motor, perceptual, and other cognitive functions (1). Abnormal levels of these monoamines have been associated with several neuropsychiatric disorders (2-5). The enzymatic metabolism of these neurotransmitters is mainly catalyzed by monoamine oxidase (MAO), a mitochondrial-bound flavoprotein (6). The two MAO isoenzymes, A and B, are encoded by different genes next to each other on the X chromosome (7), with 70% amino acid identity (8) and identical intron-exon organization (9). MAO A has a higher affinity for 5-HT, NE, and DA (6, 10). In contrast, MAO B prefers phenylethylamine (PEA) as substrate (11), although it can degrade 5-HT, NE, and DA in the absence of MAO A (12). As a consequence, the lack of both isoenzymes in mice results in significantly higher monoamine levels than those observed in single knockout (KO) counterparts (12). The deficiency of both MAO isoenzymes in humans has been found to be associated with severe intellectual and developmental disabilities, hypotonia, failure to thrive, and autisticlike symptoms (including sociocommunicative deficits and perseverative manifestations) (13-15). Although similar alterations were also featured by MAO A KO mice, the severity of the changes was typically more pervasive in MAO A/B KO mice, supporting the idea that the se...

Neuronal plasticity is regulated by the ovarian steroids estradiol (E2) and progesterone (P4) in many normal brain functions, as well as in acute response to injury and chronic neurodegenerative disease. In a female rat model of axotomy, the E2-dependent compensatory neuronal sprouting is antagonized by P4. To resolve complex glial-neuronal cell interactions, we used the "woundingin-a-dish" model of neurons cocultured with astrocytes or mixed glia (microglia to astrocytes, 1:3). Although both astrocytes and mixed glia supported E2-enhanced neurite outgrowth, P4 antagonized E2-induced neurite outgrowth only with mixed glia, but not astrocytes alone. We now show that P4-E2 antagonism of neurite outgrowth is mediated by microglial expression of progesterone receptor (Pgr) membrane component 1 (Pgrmc1)/S2R, a putative nonclassical Pgr mediator with multiple functions. The P4-E2 antagonism of neurite outgrowth was restored by add-back of microglia to astrocyte-neuron cocultures. Because microglia do not express the classical Pgr, we examined the role of Pgrmc1, which is expressed in microglia in vitro and in vivo. Knockdown by siRNA-Pgrmc1 in microglia before add-back to astrocyte-neuron cocultures suppressed the P4-E2 antagonism of neurite outgrowth. Conditioned media from microglia restored the P4-E2 activity, but only if microglia were activated by lipopolysaccharide or by wounding. Moreover, the microglial activation was blocked by Pgmrc1-siRNA knockdown. These findings explain why nonwounded cultures without microglial activation lack P4 antagonism of E2-induced neurite outgrowth. We suggest that microglial activation may influence brain responses to exogenous P4, which is a prospective therapy in traumatic brain injury. (Endocrinology 154: 2468 -2480, 2013) C ross talk between estradiol (E2) and progesterone (P4) operates throughout the female reproductive system in cycles of E2-dependent cell growth and P4-dependent cell regression. However, little is known of the brain cell interactions that enable "P4-E2 antagonism" in synaptic plasticity. In neuronal responses to injury that involve P4-E2 antagonism, we describe a novel role of microglial activation that is mediated by progesterone receptor (Pgr) membrane component 1 (Pgrmc1)/S2R, a nonclassical Pgr of emerging significance to brain neuronal functions and innate immunity.In the hippocampus, synaptic remodeling during the rat estrous cycle is driven by serial elevations of E2 and P4 (1). Neuronal sprouting in response to axotomy is also modulated by P4-E2 antagonism. In an adult rat model of entorhinal cortex lesions that axotomize the perforant pathway to the hippocampus, the ensuing compensatory neurite outgrowth into the dentate gyrus molecular layer was stimulated by E2 and blocked by concurrent administration of E2ϩP4 (2). Astrocyte and microglial activation in the deafferented zone was correspondingly modulated by E2 and P4. An unexpected role of microglia in P4-E2 antagonism of neurite outgrowth was identified with the "wounding-in-a-dish" model of ax...

Pgrmc1 (progesterone receptor membrane component 1) is a multifunctional 22 kDa protein with heme-binding and P450-activating capacity which was recognized under different names for roles in cell motility during neural development and in cancer, and apoptosis. Pgrmc1 expression in microglia was recently shown by the present authors to mediate estrogen-progesterone interactions during axonal sprouting and to mediate microglial activation itself. We also discuss other functions of Pgramc1 in the nervous system and its possible relationship to the 18 kDa sigma-2 receptor (S2R).

We recently demonstrated that human C-reactive protein (CRP), expressed hepatically in transgenic mice (CRPtg), improved the outcome of experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS). The liver is the primary site of CRP synthesis in humans and in CRPtg mice but is also expressed by both at low levels in the CNS. To determine if CNS expression of human CRP is sufficient to impact EAE, we generated neuronal CRP transgenic mice (nCRPtg) wherein human CRP expression is driven by the neuron-specific Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) gene promoter. We found that hepatically expressed/blood-borne CRP, but not CNS expressed CRP, lessened EAE severity. These outcomes indicate that the protective actions of human CRP in EAE are manifested in the periphery and not in the CNS and reveal a previously unappreciated site specificity for the beneficial actions of CRP in CNS disease.