Brain-Derived CCN3 Is An Osteoanabolic Hormone That Sustains Bone in Lactating Females

In lactating mothers, the high calcium (Ca 2+ ) demand for milk production triggers significant bone resorption. While estrogen would normally counteract excessive bone loss and maintain sufficient bone formation during this postpartum period, this sex steroid drops precipitously after giving birth. Here, we report that brain-derived CCN3 (Cellular Communication Network factor 3) secreted from KISS1 neurons of the arcuate nucleus (ARC KISS1 ) fills this void and functions as a potent osteoanabolic factor to promote bone mass in lactating females. Using parabiosis and bone transplant methods, we first established that a humoral factor accounts for the female-specific, high bone mass previously observed by our group after deleting estrogen receptor alpha (ER α ) from ARC KISS1 neurons 1 . This exceptional bone phenotype in mutant females can be traced back to skeletal stem cells (SSCs), as reflected by their increased frequency and osteochondrogenic potential. Based on multiple assays, CCN3 emerged as the most promising secreted pro-osteogenic factor from ARC KISS1 neurons, acting on mouse and human SSCs at low subnanomolar concentrations independent of age or sex. That brain-derived CCN3 promotes bone formation was further confirmed by in vivo gain- and loss-of-function studies. Notably, a transient rise in CCN3 appears in ARC KISS1 neurons in estrogen-depleted lactating females coincident with increased bone remodeling and high calcium demand. Our findings establish CCN3 as a potentially new therapeutic osteoanabolic hormone that defines a novel female-specific brain-bone axis for ensuring mammalian species survival.

An evolutionary trade-off between host immunity and metabolism drives fatty liver in male mice

Adaptations to infectious and dietary pressures shape mammalian physiology and disease risk. How such adaptations affect sex-biased diseases remains insufficiently studied. In this study, we show that sex-dependent hepatic gene programs confer a robust (~300%) survival advantage for male mice during lethal bacterial infection. The transcription factor B cell lymphoma 6 (BCL6), which masculinizes hepatic gene expression at puberty, is essential for this advantage. However, protection by BCL6 protein comes at a cost during conditions of dietary excess, which result in overt fatty liver and glucose intolerance in males. Deleting hepatic BCL6 reverses these phenotypes but markedly lowers male survival during infection, thus establishing a sex-dependent trade-off between host defense and metabolic systems. Our findings offer strong evidence that some current sex-biased diseases are rooted in ancient evolutionary trade-offs between immunity and metabolism.

Running the Female Power Grid Across Lifespan Through Brain Estrogen Signaling

The role of central estrogen in cognitive, metabolic, and reproductive health has long fascinated the lay public and scientists alike. In the last two decades, insight into estrogen signaling in the brain and its impact on female physiology is beginning to catch up with the vast information already established for its actions on peripheral tissues. Using newer methods to manipulate estrogen signaling in hormone-sensitive brain regions, neuroscientists are now identifying the molecular pathways and neuronal subtypes required for controlling sex-dependent energy allocation. However, the immense cellular complexity of these hormone-sensitive brain regions makes it clear that more research is needed to fully appreciate how estrogen modulates neural circuits to regulate physiological and behavioral end points. Such insight is essential for understanding how natural or drug-induced hormone fluctuations across lifespan affect women's health.

Chronic Stimulation of Arcuate Kiss1 Neurons Decreases Bone Mass in Female Mice

Loss of peripheral estrogen in postmenopausal women is often associated with decreased physical activity and loss of bone mass, leading to an increased risk of metabolic diseases, osteoporosis, and skeletal fragility. While it is well-established that loss of peripheral estrogen signaling results in bone loss, we previously found that eliminating central estrogen signaling paradoxically results in an unexpected massive increase in bone mass only in female mice. Specifically, deletion of estrogen receptor alpha (ERα) signaling in kisspeptin 1 (Kiss1) expressing neurons of the arcuate nucleus (ARC^Kiss1) increases bone mass at the expense of reproduction in female mice. Currently, the mechanisms and the neurocircuits that modulate these unexpected responses are unknown. Here, to begin addressing these questions, we asked if changing the neuronal output of ARC^Kiss1 neurons using chemogenetic manipulation of ARC^Kiss1 neurons might also alter bone mass and locomotion in female mice. To do this, we delivered stimulatory (AAV2-hM3Dq-mCherry) designer receptors exclusively activated by designer drugs (DREADDs) to the ARC of wild type and Kiss1-Cre+ (Kiss1-Cre^hM3q-DREADDs) female mice and asked if chronic activation of ARC^Kiss1 neurons might alter bone mass as analyzed by standard ex-vivo µCT imaging. Clozapine N-oxide (CNO) was delivered for 22 days (0.1 mg/mL). We also leveraged the ANY-Maze system to assess home cage activity over an extensive 96-hour period. Acute activation of ARC^Kiss1 tended to decrease home cage activity by nearly 40% in Kiss1-Cre^hM3q-DREADDs mice during the dark period compared to WT females. Interestingly, chronic activation of ARC^Kiss1 neurons significantly lowered trabecular bone volume by nearly 30%. Current studies are underway to ask if inhibiting ARC^Kiss1 neurons results in increased bone mass. Our findings collectively suggest that the neuronal activity of ARC^Kiss1 neurons is sufficient to shift energy allocation away from locomotion and bone-building to maximize reproductive capacity. We speculate that the widely used SERM in breast cancer treatment, Tamoxifen, might exert its bone sparing effect by silencing ARC^Kiss1 neurons.

LRH-1 regulates hepatic lipid homeostasis and maintains arachidonoyl phospholipid pools critical for phospholipid diversity

Excess lipid accumulation is an early signature of nonalcoholic fatty liver disease (NAFLD). Although liver receptor homolog 1 (LRH-1) (encoded by NR5A2) is suppressed in human NAFLD, evidence linking this phospholipid-bound nuclear receptor to hepatic lipid metabolism is lacking. Here, we report an essential role for LRH-1 in hepatic lipid storage and phospholipid composition based on an acute hepatic KO of LRH-1 in adult mice (LRH-1AAV8-Cre mice). Indeed, LRH-1-deficient hepatocytes exhibited large cytosolic lipid droplets and increased triglycerides (TGs). LRH-1-deficient mice fed high-fat diet displayed macrovesicular steatosis, liver injury, and glucose intolerance, all of which were reversed or improved by expressing wild-type human LRH-1. While hepatic lipid synthesis decreased and lipid export remained unchanged in mutants, elevated circulating free fatty acid helped explain the lipid imbalance in LRH-1AAV8-Cre mice. Lipidomic and genomic analyses revealed that loss of LRH-1 disrupts hepatic phospholipid composition, leading to lowered arachidonoyl (AA) phospholipids due to repression of Elovl5 and Fads2, two critical genes in AA biosynthesis. Our findings reveal a role for the phospholipid sensor LRH-1 in maintaining adequate pools of hepatic AA phospholipids, further supporting the idea that phospholipid diversity is an important contributor to healthy hepatic lipid storage.

Techniques for Evaluation of AR Transcriptional Output and Recruitment to DNA

Steroid receptors are ligand activated transcription factors whose promoter specificity is regulated by a broad set of coregulators and pioneer factors. Corepressors and coactivators determine receptors' recruitment to specific regulatory elements and ultimately their transcriptional output. Using androgen receptor (AR) and NCOR1 corepressor as examples, this chapter describes experimental approaches to evaluate recruitment of steroid receptors and their coregulators to DNA and to determine coregulator contribution to the transcriptional output of the receptor. The chromatin immunoprecipitation assay, or ChIP, quantifies protein-DNA interaction in the cellular chromatin environment. Here, we describe a protocol to measure NCOR1 recruitment to AR binding sites of interest using ChIP. Gene Set Enrichment Analysis, GSEA, is a computational technique to determine whether a defined gene set is significantly represented among changes in gene expression between two biological groups. As an example, we examine whether AR repressed genes are significantly represented among genes altered by the NCOR1 knockout.

Abstract 281: Hepatic Liver Receptor Homolog-1, a Key Regulator of Lipid Storage and Phospholipid Diversity

Cardiovascular disease and malignancy are the most common cause of death in Non-alcoholic Steatohepatitis (NASH) patients. Aside from lifestyle modification, there is currently no treatment for NASH. Activation of Liver Receptor Homolog-1 (Lrh-1), known to bind phospholipid ligands, has been shown to effectively reduce liver triglyceride (TG) in DIO mice, raising Lrh-1 as a possible target for treating NASH. Despite this finding, hepatic TGs are equivalent in controls and liver-specific Lrh-1 knockout (LKO or Lrh1 AlbCre ) mice, regardless of diet. Given this discrepancy, we sought to characterize Lrh-1’s role in hepatic lipid metabolism by acutely deleting Lrh-1 in the adult liver, thus eliminating potential compensatory developmental effects associated with LKO. To acutely eliminate Lrh-1 in hepatocytes, 6-week old Lrh-1 fl/f l male mice were infected with AVV8-TBG-eGFP (Control) or AAV8-TBG-Cre (LKO AAVCre ) via retro-orbital injection and fed chow or high fat diet. LKO AAVCre mice developed hepatic steatosis after six weeks on standard chow or high fat diet. Furthermore, LKO AAVCre hepatocytes exhibited large lipid droplets, which were visible as early as 2 wks post-infection, thus suggesting that lipid handling is significantly altered in LKO AAVCre hepatocytes, independent of fatty acid transport or oxidation. LKO AAVCre exhibited lower Pcsk9 expression, which correlated with decreased fasting plasma LDL-C. Consistent with other studies showing that perturbations in phospholipid pools affect lipid storage, lipidomic analyses revealed a significant reduction in phospholipid species containing arachidonic acid (AA), thus reducing the overall diversity of key membrane phospholipids. RNA-Seq analyses from LKO AAVCre livers confirmed that factors promoting lipid droplet size ( Cidec , Plin4 ) were greatly increased while key enzymes in biosynthesis of unsaturated fatty acids were reduced ( Fads1, Fads2 and Elovl5 ). In addition, expression of human LRH-1 in LKO AAVCre decreased hepatic TG and improved glucose tolerance in DIO mice, in a ligand dependent manner. Collectively our data establish a novel role for Lrh-1 as a key regulator of lipid storage, thereby providing the first in vivo evidence as to why phospholipid serve as Lrh-1 ligands.

Testosterone Rapidly Augments Retrograde Endocannabinoid Signaling in Proopiomelanocortin Neurons to Suppress Glutamatergic Input from Steroidogenic Factor 1 Neurons via Upregulation of Diacylglycerol Lipase-α

Testosterone exerts profound effects on reproduction and energy homeostasis. Like other orexigenic hormones, it increases endocannabinoid tone within the hypothalamic feeding circuitry. Therefore, we tested the hypothesis that testosterone upregulates the expression of diacylglycerol lipase (DAGL)α in the hypothalamic arcuate nucleus (ARC) to increase energy intake via enhanced endocannabinoid-mediated retrograde inhibition of anorexigenic proopiomelanocortin (POMC) neurons. Energy intake, meal patterns, and energy expenditure were evaluated in orchidectomized, male guinea pigs treated subcutaneously with testosterone propionate (TP; 400 μg) or its sesame oil vehicle (0.1 mL). TP rapidly increased energy intake, meal size, O2 consumption, CO2 production, and metabolic heat production, all of which were antagonized by prior administration of the DAGL inhibitor orlistat (3 μg) into the third ventricle. These orlistat-sensitive, TP-induced increases in energy intake and expenditure were temporally associated with a significant elevation in ARC DAGLα expression. Electrophysiological recordings in hypothalamic slices revealed that TP potentiated depolarization-induced suppression of excitatory glutamatergic input onto identified ARC POMC neurons, which was also abolished by orlistat (3 μM), the CB1 receptor antagonist AM251 (1 μM), and the AMP-activated protein kinase inhibitor compound C (30 μM) and simulated by transient bath application of the dihydrotestosterone mimetic Cl-4AS-1 (100 nM) and testosterone-conjugated bovine serum albumin (100 nM). Thus, testosterone boosts DAGLα expression to augment retrograde, presynaptic inhibition of glutamate release onto ARC POMC neurons that, in turn, increases energy intake and expenditure. These studies advance our understanding of how androgens work within the hypothalamic feeding circuitry to affect changes in energy balance.

Sex-dependent changes in metabolism and behavior, as well as reduced anxiety after eliminating ventromedial hypothalamus excitatory output

Objectives

The ventromedial hypothalamic nucleus (VMH) regulates energy homeostasis as well as social and emotional behaviors. Nearly all VMH neurons, including those in the sexually dimorphic ventrolateral VMH (VMHvl) subregion, release the excitatory neurotransmitter glutamate and use the vesicular glutamate transporter 2 (Vglut2). Here, we asked how glutamatergic signaling contributes to the collective metabolic and behavioral responses attributed to the VMH and VMHvl.

Methods

Using Sf1-Cre and a Vglut2 floxed allele, Vglut2 was knocked-out in SF-1 VMH neurons (Vglut2^Sf1-Cre). Metabolic and neurobehavioral assays were carried out initially on Vglut2^fl/fl and Vglut2^Sf1-Cre mice in a mixed, and then in the C57BL/6 genetic background, which is prone to hyperglycemia and diet induced obesity (DIO).

Results

Several phenotypes observed in Vglut2^Sf1-Cre mice were largely unexpected based on prior studies that have perturbed VMH development or VMH glutamate signaling. In our hands, Vglut2^Sf1-Cre mice failed to exhibit the anticipated increase in body weight after high fat diet (HFD) or the impaired glucose homeostasis after fasting. Instead, there was a significant sex-dependent attenuation of DIO in Vglut2^Sf1-Cre females. Vglut2^Sf1-Cre males also display a sex-specific loss of conditioned-fear responses and aggression accompanied by more novelty-associated locomotion. Finally, unlike the higher anxiety noted in Sf1^Nestin-Cre mice that lack a fully formed VMH, both male and female Vglut2^Sf1-Cre mice were less anxious.

Conclusions

Loss of VMH glutamatergic signaling sharply decreased DIO in females, attenuated aggression and learned fear in males, and was anxiolytic in males and females. Collectively, our findings demonstrate that while glutamatergic output from the VMH appears largely dispensable for counter regulatory responses to hypoglycemia, it drives sex-dependent differences in metabolism and social behaviors and is essential for adaptive responses to anxiety-provoking stimuli in both sexes.

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Excitatory VMH output controls sex-dependent metabolic and behavioral phenotypes.

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Vglut2^Sf1-Cre mice are not prone to diet-induced obesity or glucose misregulation.

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Loss of VMH glutamatergic signaling leads to negative energy state in females.

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Aggression and learned fear are lower in males lacking VMH excitatory output.

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VMH glutamatergic signaling drives normal anxiety responses in both sexes.

Olfactory memory traces in Drosophila

In Drosophila, the fruit fly, coincident exposure to an odor and an aversive electric shock can produce robust behavioral memory. This behavioral memory is thought to be regulated by cellular memory traces within the central nervous system of the fly. These molecular, physiological, or structural changes in neurons, induced by pairing odor and shock, regulate behavior by altering the neurons' response to the learned environment. Recently, novel in vivo functional imaging techniques have allowed researchers to observe cellular memory traces in intact animals. These investigations have revealed interesting temporal and spatial dynamics of cellular memory traces. First, a short-term cellular memory trace was discovered that exists in the antennal lobe, an early site of olfactory processing. This trace represents the recruitment of new synaptic activity into the odor representation and forms for only a short period of time just after training. Second, an intermediate-term cellular memory trace was found in the dorsal paired medial neuron, a neuron thought to play a role in stabilizing olfactory memories. Finally, a long-term protein synthesis-dependent cellular memory trace was discovered in the mushroom bodies, a structure long implicated in olfactory learning and memory. Therefore, it appears that aversive olfactory associations are encoded by multiple cellular memory traces that occur in different regions of the brain with different temporal domains.

Repressors of androgen and progesterone receptor action

Androgen and progesterone receptors (AR and PR) are two determining factors in gonadal differentiation that are highly expressed in developing and mature gonads. Loss of AR results in XY sex reversal and mutations causing reduced AR activity lead to varying degrees of defects in masculinization. Female PR knockout mice are infertile due to ovarian defects. While much has been discovered about positive regulation of these receptors by coactivators little is known about repression of the transcriptional activity of AR and PR in the presence of agonists. In this study we assessed the effect of SMRT and DAX-1 on AR and PR activity in the presence of both agonists and partial antagonists. We show that SMRT and DAX-1 repress agonist-dependent activity of both receptors, and the mechanism of repression includes disruption of the receptor dimer interactions rather than recruitment of histone deacetylases. We demonstrate that endogenous agonist-bound PR and DAX-1 in T47D breast cancer cells and endogenous AR and DAX-1 in LNCaP prostate cancer cells can be coimmunoprecipitated suggesting that the interaction is physiological. Surprisingly, although DAX-1 represses partial antagonist activity of AR, it was ineffective in repressing partial antagonist induced activity of PR. In contrast to most reported repressors, the expression of DAX-1 is restricted. We found that although DAX-1 is expressed in normal human prostate, its expression is strongly reduced in benign prostatic hyperplasia suggesting that DAX-1 plays a role in limiting AR activity in prostate.