Travelling under pressure - hypoxia and shear stress in the metastatic journey

Cancer cell invasion, intravasation and survival in the bloodstream are early steps of the metastatic process, pivotal to enabling the spread of cancer to distant tissues. Circulating tumor cells (CTCs) represent a highly selected subpopulation of cancer cells that tamed these critical steps, and a better understanding of their biology and driving molecular principles may facilitate the development of novel tools to prevent metastasis. Here, we describe key research advances in this field, aiming at describing early metastasis-related processes such as collective invasion, shedding, and survival of CTCs in the bloodstream, paying particular attention to microenvironmental factors like hypoxia and mechanical stress, considered as important influencers of the metastatic journey.

The peroxisome: an up-and-coming organelle in immunometabolism

Peroxisomes are essential metabolic organelles, well known for their roles in the metabolism of complex lipids and reactive ionic species. In the past 10 years, peroxisomes have also been cast as central regulators of immunity. Lipid metabolites of peroxisomes, such as polyunsaturated fatty acids (PUFAs), are precursors for important immune mediators, including leukotrienes (LTs) and resolvins. Peroxisomal redox metabolism modulates cellular immune signaling such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. Additionally, peroxisomal β-oxidation and ether lipid synthesis control the development and aspects of the activation of both innate and adaptive immune cells. Finally, peroxisome number and metabolic activity have been linked to inflammatory diseases. These discoveries have opened avenues of investigation aimed at targeting peroxisomes for therapeutic intervention in immune disorders, inflammation, and cancer.

A Functional SMAD2/3 Binding Site in the PEX11β Promoter Identifies a Role for TGFβ in Peroxisome Proliferation in Humans

In mammals, peroxisomes perform crucial functions in cellular metabolism, signaling and viral defense which are essential to the viability of the organism. Molecular cues triggered by changes in the cellular environment induce a dynamic response in peroxisomes, which manifests itself as a change in peroxisome number, altered enzyme levels and adaptations to the peroxisomal morphology. How the regulation of this process is integrated into the cell's response to different stimuli, including the signaling pathways and factors involved, remains unclear. Here, a cell-based peroxisome proliferation assay has been applied to investigate the ability of different stimuli to induce peroxisome proliferation. We determined that serum stimulation, long-chain fatty acid supplementation and TGFβ application all increase peroxisome elongation, a prerequisite for proliferation. Time-resolved mRNA expression during the peroxisome proliferation cycle revealed a number of peroxins whose expression correlated with peroxisome elongation, including the β isoform of PEX11, but not the α or γ isoforms. An initial map of putative regulatory motif sites in the respective promoters showed a difference between binding sites in PEX11α and PEX11β, suggesting that these genes may be regulated by distinct pathways. A functional SMAD2/3 binding site in PEX11β points to the involvement of the TGFβ signaling pathway in expression of this gene and thus peroxisome proliferation/dynamics in humans.

Functional Peroxisomes Are Essential for Efficient Cholesterol Sensing and Synthesis

Cholesterol biosynthesis is a multi-step process involving several subcellular compartments, including peroxisomes. Cells adjust their sterol content by both transcriptional and post-transcriptional feedback regulation, for which sterol regulatory element-binding proteins (SREBPs) are essential; such homeostasis is dysregulated in peroxisome-deficient Pex2 knockout mice. Here, we compared the regulation of cholesterol biosynthesis in Chinese hamster ovary (CHO-K1) cells and in three isogenic peroxisome-deficient CHO cell lines harboring Pex2 gene mutations. Peroxisome deficiency activated expression of cholesterogenic genes, however, cholesterol levels were unchanged. 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) protein levels were increased in mutant cells, whereas HMGCR activity was significantly decreased, resulting in reduced cholesterol synthesis. U18666A, an inhibitor of lysosomal cholesterol export, induced cholesterol biosynthetic enzymes; yet, cholesterol synthesis was still reduced. Interestingly, peroxisome deficiency promoted ER-to-Golgi SREBP cleavage-activating protein (SCAP) trafficking even when cells were cholesterol-loaded. Restoration of functional peroxisomes normalized regulation of cholesterol synthesis and SCAP trafficking. These results highlight the importance of functional peroxisomes for maintaining cholesterol homeostasis and efficient cholesterol synthesis.

A Single Metabolite which Modulates Lipid Metabolism Alters Hematopoietic Stem/Progenitor Cell Behavior and Promotes Lymphoid Reconstitution

Fatty acid β-oxidation (FAO), the breakdown of lipids, is a metabolic pathway used by various stem cells. FAO levels are generally high during quiescence and downregulated with proliferation. The endogenous metabolite malonyl-CoA modulates lipid metabolism as a reversible FAO inhibitor and as a substrate for de novo lipogenesis. Here we assessed whether malonyl-CoA can be exploited to steer the behavior of hematopoietic stem/progenitor cells (HSPCs), quiescent stem cells of clinical relevance. Treatment of mouse HSPCs in vitro with malonyl-CoA increases HSPC numbers compared with nontreated controls and ameliorates blood reconstitution capacity when transplanted in vivo, mainly through enhanced lymphoid reconstitution. Similarly, human HSPC numbers also increase upon malonyl-CoA treatment in vitro. These data corroborate that lipid metabolism can be targeted to direct cell fate and stem cell proliferation. Physiological modulation of metabolic pathways, rather than genetic or pharmacological inhibition, provides unique perspectives for stem cell manipulations in health and disease.

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Modulating lipid metabolism with malonyl-CoA increases murine HSPCs in vitro

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Malonyl-CoA promotes lymphoid cell fate of HSPCs in vitro and in vivo

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The myeloid bias in aged HSPCs is partially recovered with malonyl-CoA exposure

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Malonyl-CoA increases the numbers of human HSPCs in vitro

Peroxisome-Deficiency and HIF-2α Signaling Are Negative Regulators of Ketohexokinase Expression

Ketohexokinase (KHK) is the first and rate-limiting enzyme of fructose metabolism. Expression of the two alternatively spliced KHK isoforms, KHK-A and KHK-C, is tissue-specific and KHK-C is predominantly expressed in liver, kidney and intestine and responsible for the fructose-catabolizing function. While KHK isoform choice has been linked to the development of disorders such as obesity, diabetes, cardiovascular disease and cancer, little is known about the regulation of total KHK expression. In the present study, we investigated how hypoxic signaling influences fructose metabolism in the liver. Hypoxia or von Hippel-Lindau (VHL) tumor suppressor loss leads to the stabilization of hypoxia-inducible factors alpha (HIF-1α and HIF-2α) and the activation of their signaling to mediate adaptive responses. By studying liver-specific Vhl, Vhl/Hif1a, and Vhl/Epas1 knockout mice, we found that KHK expression is suppressed by HIF-2α (encoded by Epas1) but not by HIF-1α signaling on mRNA and protein levels. Reduced KHK levels were accompanied by downregulation of aldolase B (ALDOB) in the livers of Vhl and Vhl/Hif1a knockout mice, further indicating inhibited fructose metabolism. HIF-1α and HIF-2α have both overlapping and distinct target genes but are differentially regulated depending on the cell type and physiologic or pathologic conditions. HIF-2α activation augments peroxisome degradation in mammalian cells by pexophagy and thereby changes lipid composition reminiscent of peroxisomal disorders. We further demonstrated that fructose metabolism is negatively regulated by peroxisome-deficiency in a Pex2 knockout Zellweger mouse model, which lacks functional peroxisomes and is characterized by widespread metabolic dysfunction. Repression of fructolytic genes in Pex2 knockout mice appeared to be independent of PPARα signaling and nutritional status. Interestingly, our results demonstrate that both HIF-2α and peroxisome-deficiency result in downregulation of Khk independent of splicing as both isoforms, Khka as well as Khkc, are significantly downregulated. Hence, our study offers new and unexpected insights into the general regulation of KHK, and therefore fructolysis. We revealed a novel regulatory function of HIF-2α, suggesting that HIF-1α and HIF-2α have tissue-specific opposing roles in the regulation of Khk expression, isoform choice and fructolysis. In addition, we discovered a previously unknown function of peroxisomes in the regulation of fructose metabolism.

FASN-Dependent Lipid Metabolism Links Neurogenic Stem/Progenitor Cell Activity to Learning and Memory Deficits

Altered neural stem/progenitor cell (NSPC) activity and neurodevelopmental defects are linked to intellectual disability. However, it remains unclear whether altered metabolism, a key regulator of NSPC activity, disrupts human neurogenesis and potentially contributes to cognitive defects. We investigated links between lipid metabolism and cognitive function in mice and human embryonic stem cells (hESCs) expressing mutant fatty acid synthase (FASN; R1819W), a metabolic regulator of rodent NSPC activity recently identified in humans with intellectual disability. Mice homozygous for the FASN R1812W variant have impaired adult hippocampal NSPC activity and cognitive defects because of lipid accumulation in NSPCs and subsequent lipogenic ER stress. Homozygous FASN R1819W hESC-derived NSPCs show reduced rates of proliferation in embryonic 2D cultures and 3D forebrain regionalized organoids, consistent with a developmental phenotype. These data from adult mouse models and in vitro models of human brain development suggest that altered lipid metabolism contributes to intellectual disability.

High-throughput screening in multicellular spheroids for target discovery in the tumor microenvironment

INTRODUCTION

Solid tumors are highly influenced by a complex tumor microenvironment (TME) that cannot be modeled with conventional two-dimensional (2D) cell culture. In addition, monolayer culture conditions tend to induce undesirable molecular and phenotypic cellular changes. The discrepancy between in vitro and in vivo is an important factor accounting for the high failure rate in drug development. Three-dimensional (3D) multicellular tumor spheroids (MTS) more closely resemble the in vivo situation in avascularized tumors.

AREAS COVERED

This review describes the use of MTS for anti-cancer drug discovery, with an emphasis on high-throughput screening (HTS) compatible assays. In particular, we focus on how these assays can be used for target discovery in the context of the TME.

EXPERT OPINION

Arrayed MTS in microtiter plates are HTS compatible but remain more expensive and time consuming than their 2D culture counterpart. It is therefore imperative to use assays with multiplexed readouts, in order to maximize the information that can be gained with the screen. In this context, high-content screening allowing to uncover microenvironmental dependencies is the true added value of MTS-based screening compared to 2D culture-based screening. Hit translation in animal models will, however, be key to allow a broader use of MTS-based screening in industry.

A Fatty Acid Oxidation-dependent Metabolic Shift Regulates the Adaptation of BRAF-mutated Melanoma to MAPK Inhibitors

PURPOSE

Treatment of BRAF^V600E -mutant melanomas with MAPK inhibitors (MAPKi) results in significant tumor regression, but acquired resistance is pervasive. To understand nonmutational mechanisms underlying the adaptation to MAPKi and to identify novel vulnerabilities of melanomas treated with MAPKi, we focused on the initial response phase during treatment with MAPKi.

EXPERIMENTAL DESIGN

By screening proteins expressed on the cell surface of melanoma cells, we identified the fatty acid transporter CD36 as the most consistently upregulated protein upon short-term treatment with MAPKi. We further investigated the effects of MAPKi on fatty acid metabolism using in vitro and in vivo models and analyzing patients' pre- and on-treatment tumor specimens.

RESULTS

Melanoma cells treated with MAPKi displayed increased levels of CD36 and of PPARα-mediated and carnitine palmitoyltransferase 1A (CPT1A)-dependent fatty acid oxidation (FAO). While CD36 is a useful marker of melanoma cells during adaptation and drug-tolerant phases, the upregulation of CD36 is not functionally involved in FAO changes that characterize MAPKi-treated cells. Increased FAO is required for BRAF^V600E -mutant melanoma cells to survive under the MAPKi-induced metabolic stress prior to acquiring drug resistance. The upfront and concomitant inhibition of FAO, glycolysis, and MAPK synergistically inhibits tumor cell growth in vitro and in vivo.

CONCLUSIONS

Thus, we identified a clinically relevant therapeutic approach that has the potential to improve initial responses and to delay acquired drug resistance of BRAF^V600E -mutant melanoma.

BRAF inhibition sensitizes melanoma cells to α-amanitin via decreased RNA polymerase II assembly

Despite the great success of small molecule inhibitors in the treatment of patients with BRAF^V600E mutated melanoma, the response to these drugs remains transient and patients eventually relapse within a few months, highlighting the need to develop novel combination therapies based on the understanding of the molecular changes induced by BRAF^V600E inhibitors. The acute inhibition of oncogenic signaling can rewire entire cellular signaling pathways and thereby create novel cancer cell vulnerabilities. Here, we demonstrate that inhibition of BRAF^V600E oncogenic signaling in melanoma cell lines leads to destabilization of the large subunit of RNA polymerase II POLR2A (polymerase RNA II DNA-directed polypeptide A), thereby preventing its binding to the unconventional prefoldin RPB5 interactor (URI1) chaperone complex and the successful assembly of RNA polymerase II holoenzymes. Furthermore, in melanoma cell lines treated with mitogen-activated protein kinase (MAPK) inhibitors, α-amanitin, a specific and irreversible inhibitor of RNA polymerase II, induced massive apoptosis. Pre-treatment of melanoma cell lines with MAPK inhibitors significantly reduced IC50 values to α-amanitin, creating a state of collateral vulnerability similar to POLR2A hemizygous deletions. Thus, the development of melanoma specific α-amanitin antibody-drug conjugates could represent an interesting therapeutic approach for combination therapies with BRAF^V600E inhibitors.

Correction of gene model annotations improves isoform abundance estimates: the example of ketohexokinase ( Khk)

Next generation sequencing protocols such as RNA-seq have made the genome-wide characterization of the transcriptome a crucial part of many research projects in biology. Analyses of the resulting data provide key information on gene expression and in certain cases on exon or isoform usage. The emergence of transcript quantification software such as Salmon has enabled researchers to efficiently estimate isoform and gene expressions across the genome while tremendously reducing the necessary computational power. Although overall gene expression estimations were shown to be accurate, isoform expression quantifications appear to be a more challenging task. Low expression levels and uneven or insufficient coverage were reported as potential explanations for inconsistent estimates. Here, through the example of the ketohexokinase ( Khk) gene in mouse, we demonstrate that the use of an incorrect gene annotation can also result in erroneous isoform quantification results. Manual correction of the input Khk gene model provided a much more accurate estimation of relative Khk isoform expression when compared to quantitative PCR (qPCR measurements). In particular, removal of an unexpressed retained intron and a proper adjustment of the 5’ and 3’ untranslated regions both had a strong impact on the correction of erroneous estimates. Finally, we observed a better concordance in isoform quantification between datasets and sequencing strategies when relying on the newly generated Khk annotations. These results highlight the importance of accurate gene models and annotations for correct isoform quantification and reassert the need for orthogonal methods of estimation of isoform expression to confirm important findings.

A Fatty Acid Oxidation-Dependent Metabolic Shift Regulates Adult Neural Stem Cell Activity

Hippocampal neurogenesis is important for certain forms of cognition, and failing neurogenesis has been implicated in neuropsychiatric diseases. The neurogenic capacity of hippocampal neural stem/progenitor cells (NSPCs) depends on a balance between quiescent and proliferative states. Here, we show that the rate of fatty acid oxidation (FAO) regulates the activity of NSPCs. Quiescent NSPCs show high levels of carnitine palmitoyltransferase 1a (Cpt1a)-dependent FAO, which is downregulated in proliferating NSPCs. Pharmacological inhibition and conditional deletion of Cpt1a in vitro and in vivo leads to altered NSPC behavior, showing that Cpt1a-dependent FAO is required for stem cell maintenance and proper neurogenesis. Strikingly, manipulation of malonyl-CoA, the metabolite that regulates levels of FAO, is sufficient to induce exit from quiescence and to enhance NSPC proliferation. Thus, the data presented here identify a shift in FAO metabolism that governs NSPC behavior and suggest an instructive role for fatty acid metabolism in regulating NSPC activity.

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A metabolic shift defines NSPC quiescence versus proliferation

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Quiescent NSPCs require high levels of FAO

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Changing levels of a single metabolite is sufficient to induce NSPC proliferation

Repository corticotrophin injection exerts direct acute effects on human B cell gene expression distinct from the actions of glucocorticoids

Repository corticotrophin injection (RCI, H.P Acthar^® gel) has been approved for use in the management of multiple autoimmune and inflammatory diseases for more than a half-century, but its mechanism of action is not well understood. We used RNA-Seq methods to define RCI-regulated mRNAs in cultured human B cells under conditions of activation by interleukin (IL)-4 and CD40 ligand. Following IL-4/CD40L activation and RCI treatment we found up-regulation of 115 unique mRNA transcripts and down-regulation of 80 unique mRNAs. The effect on these RNA levels was dose-dependent for RCI and was distinct from changes in mRNA expression induced by treatment with a potent synthetic glucocorticoid. RCI down-regulated mRNAs were observed to include a significant over-representation of genes critical for B cell proliferation under activating conditions. These data confirm that RCI exerts direct effects on human B cells to modulate mRNA expression in specific pathways of importance to B cell function and that, at the molecular level, the effects of RCI are distinct from those exerted by glucocorticoids.

EPAS1/HIF-2α is a driver of mammalian pexophagy

Oxygen (O2) is an essential substrate in cellular metabolism and signaling and as such is linked to the survival and normal function of metazoans. Central to the molecular mechanisms underlying O2 homeostasis are hypoxia-inducible factors (HIFs), heterodimeric transcription factors composed of O2-regulated α subunits (HIF1A/HIF-1α or EPAS1/HIF-2α), and a constitutively expressed ARNT/HIF-1β subunit, that serve as master regulators of the adaptive response to hypoxia. HIF1A and EPAS1 have both unique and overlapping functions in the regulation of diverse cellular processes, but so far there has been no evidence linking HIF signaling to peroxisomes. In a recent study we identified a unique function of EPAS1 as promoter of pexophagy in hepatocytes. Here we summarize our findings and discuss potential mechanisms by which EPAS1 might trigger pexophagy.

Hypoxia signaling pathways: modulators of oxygen-related organelles

Oxygen (O2) is an essential substrate in cellular metabolism, bioenergetics, and signaling and as such linked to the survival and normal function of all metazoans. Low O2 tension (hypoxia) is a fundamental feature of physiological processes as well as pathophysiological conditions such as cancer and ischemic diseases. Central to the molecular mechanisms underlying O2 homeostasis are the hypoxia-inducible factors-1 and -2 alpha (HIF-1α and EPAS1/HIF-2α) that function as master regulators of the adaptive response to hypoxia. HIF-induced genes promote characteristic tumor behaviors, including angiogenesis and metabolic reprogramming. The aim of this review is to critically explore current knowledge of how HIF-α signaling regulates the abundance and function of major O2-consuming organelles. Abundant evidence suggests key roles for HIF-1α in the regulation of mitochondrial homeostasis. An essential adaptation to sustained hypoxia is repression of mitochondrial respiration and induction of glycolysis. HIF-1α activates several genes that trigger mitophagy and represses regulators of mitochondrial biogenesis. Several lines of evidence point to a strong relationship between hypoxia, the accumulation of misfolded proteins in the endoplasmic reticulum, and activation of the unfolded protein response. Surprisingly, although peroxisomes depend highly on molecular O2 for their function, there has been no evidence linking HIF signaling to peroxisomes. We discuss our recent findings that establish HIF-2α as a negative regulator of peroxisome abundance and suggest a mechanism by which cells attune peroxisomal function with O2 availability. HIF-2α activation augments peroxisome turnover by pexophagy and thereby changes lipid composition reminiscent of peroxisomal disorders. We discuss potential mechanisms by which HIF-2α might trigger pexophagy and place special emphasis on the potential pathological implications of HIF-2α-mediated pexophagy for human health.

Differential basolateral-apical distribution of scavenger receptor, class B, type I in cultured cells and the liver

The high-density lipoprotein (HDL) receptor, scavenger receptor class B, type I (SR-BI), mediates selective cholesteryl ester uptake into the liver, which finally results in cholesterol secretion into the bile. Despite several reports, the distribution of hepatic SR-BI between the sinusoidal and canalicular membranes is still under debate. We present immunohistological data using specific markers showing that the bulk of SR-BI is present in sinusoidal membranes and, to a lesser extent, in canalicular membranes in murine and human liver sections. In addition, SR-BI was detected in preparations of rat liver canalicular membranes. We also compared the in vivo findings to HepG2 cells, a widely used in vitro hepatocyte model. Interestingly, SR-BI was enriched in bile canalicular-like (BC-like) structures in polarized HepG2 cells, which were cultivated either conventionally to form a monolayer or in Matrigel to form three-dimensional structures. Fluorescently labeled HDL was transported into close proximity of BC-like structures, whereas HDL labeled with the fluorescent cholesterol analog BODIPY-cholesterol was clearly detected within these structures. Importantly, similarly to human and mouse liver, SR-BI was localized in basolateral membranes in three-dimensional liver microtissues from primary human liver cells. Our results demonstrate that SR-BI is highly enriched in sinusoidal membranes and is also found in canalicular membranes. There was no significant basolateral-apical redistribution of hepatic SR-BI in fasting and refeeding experiments in mice. Furthermore, in vitro studies in polarized HepG2 cells showed explicit differences as SR-BI was highly enriched in BC-like structures. These structures are, however, functional and accumulated HDL-derived cholesterol. Thus, biological relevant model systems should be employed when investigating SR-BI distribution in vitro.

Hif-2α promotes degradation of mammalian peroxisomes by selective autophagy

Peroxisomes play a central role in lipid metabolism, and their function depends on molecular oxygen. Low oxygen tension or von Hippel-Lindau (Vhl) tumor suppressor loss is known to stabilize hypoxia-inducible factors alpha (Hif-1α and Hif-2α) to mediate adaptive responses, but it remains unknown if peroxisome homeostasis and metabolism are interconnected with Hif-α signaling. By studying liver-specific Vhl, Vhl/Hif1α, and Vhl/Hif2α knockout mice, we demonstrate a regulatory function of Hif-2α signaling on peroxisomes. Hif-2α activation augments peroxisome turnover by selective autophagy (pexophagy) and thereby changes lipid composition reminiscent of peroxisomal disorders. The autophagy receptor Nbr1 localizes to peroxisomes and is likewise degraded by Hif-2α-mediated pexophagy. Furthermore, we demonstrate that peroxisome abundance is reduced in VHL-deficient human clear cell renal cell carcinomas with high HIF-2α levels. These results establish Hif-2α as a negative regulator of peroxisome abundance and metabolism and suggest a mechanism by which cells attune peroxisomal function with oxygen availability.

High-density lipoprotein endocytosis in endothelial cells

AIM: To describe the way stations of high-density lipoprotein (HDL) uptake and its lipid exchange in endothelial cells in vitro and in vivo.

METHODS: A combination of fluorescence microscopy using novel fluorescent cholesterol surrogates and electron microscopy was used to analyze HDL endocytosis in great detail in primary human endothelial cells. Further, HDL uptake was quantified using radio-labeled HDL particles. To validate the in vitro findings mice were injected with fluorescently labeled HDL and particle uptake in the liver was analyzed using fluorescence microscopy.

RESULTS: HDL uptake occurred via clathrin-coated pits, tubular endosomes and multivesicular bodies in human umbilical vein endothelial cells. During uptake and resecretion, HDL-derived cholesterol was exchanged at a faster rate than cholesteryl oleate, resembling the HDL particle pathway seen in hepatic cells. In addition, lysosomes were not involved in this process and thus HDL degradation was not detectable. In vivo, we found HDL mainly localized in mouse hepatic endothelial cells. HDL was not detected in parenchymal liver cells, indicating that lipid transfer from HDL to hepatocytes occurs primarily via scavenger receptor, class B, type I mediated selective uptake without concomitant HDL endocytosis.

CONCLUSION: HDL endocytosis occurs via clathrin-coated pits, tubular endosomes and multivesicular bodies in human endothelial cells. Mouse endothelial cells showed a similar HDL uptake pattern in vivo indicating that the endothelium is one major site of HDL endocytosis and transcytosis.

Endoplasmic reticulum stress impairs cholesterol efflux and synthesis in hepatic cells

Metabolic disorders such as type 2 diabetes cause hepatic endoplasmic reticulum (ER) stress, which affects neutral lipid metabolism. However, the role of ER stress in cholesterol metabolism is incompletely understood. Here, we show that induction of acute ER stress in human hepatic HepG2 cells reduced ABCA1 expression and caused ABCA1 redistribution to tubular perinuclear compartments. Consequently, cholesterol efflux to apoA-I, a key step in nascent HDL formation, was diminished by 80%. Besides ABCA1, endogenous apoA-I expression was reduced upon ER stress induction, which contributed to reduced cholesterol efflux. Liver X receptor, a key regulator of ABCA1 in peripheral cells, was not involved in this process. Despite reduced cholesterol efflux, cellular cholesterol levels remained unchanged during ER stress. This was due to impaired de novo cholesterol synthesis by reduction of HMG-CoA reductase activity by 70%, although sterol response element-binding protein-2 activity was induced. In mice, ER stress induction led to a marked reduction of hepatic ABCA1 expression. However, HDL cholesterol levels were unaltered, presumably because of scavenger receptor class B, type I downregulation under ER stress. Taken together, our data suggest that ER stress in metabolic disorders reduces HDL biogenesis due to impaired hepatic ABCA1 function.

Metabolic control of adult neural stem cell activity by Fasn-dependent lipogenesis

Mechanisms controlling the proliferative activity of neural stem and progenitor cells (NSPCs) have a pivotal role to ensure life-long neurogenesis in the mammalian brain. How metabolic programs are coupled with NSPC activity remains unknown. Here we show that fatty acid synthase (Fasn), the key enzyme of de novo lipogenesis, is highly active in adult NSPCs and that conditional deletion of Fasn in mouse NSPCs impairs adult neurogenesis. The rate of de novo lipid synthesis and subsequent proliferation of NSPCs is regulated by Spot14, a gene previously implicated in lipid metabolism, that we found to be selectively expressed in low proliferating adult NSPCs. Spot14 reduces the availability of malonyl-CoA, which is an essential substrate for Fasn to fuel lipogenesis. Thus, we identify here a functional coupling between the regulation of lipid metabolism and adult NSPC proliferation.

Peroxisome deficiency-induced ER stress and SREBP-2 pathway activation in the liver of newborn PEX2 knock-out mice

Disruption of the Pex2 gene leads to peroxisome deficiency and widespread metabolic dysfunction. We previously demonstrated that peroxisomes are critical for maintaining cholesterol homeostasis, using peroxisome-deficient Pex2(-/-) mice on a hybrid Swiss Webster×129S6/SvEv (SW/129) genetic background. Peroxisome deficiency activates hepatic endoplasmic reticulum (ER) stress pathways, leading to dysregulation of the endogenous sterol response mechanism. Herein, we demonstrate a more profound dysregulation of cholesterol homeostasis in newborn Pex2(-/-) mice congenic on a 129S6/SvEv (129) genetic background, and substantial differences between newborn versus postnatal Pex2(-/-) mice in factors that activate ER stress. These differences extend to relationships between activation of genes regulated by SREBP-2 versus PPARα. The SREBP-2 pathway is induced in neonatal Pex2(-/-) livers from 129 and SW/129 strains, despite normal hepatic cholesterol levels. ER stress markers are increased in newborn 129 Pex2(-/-) livers, which occurs in the absence of hepatic steatosis or accumulation of peroxins in the ER. Moreover, the induction of SREBP-2 and ER stress pathways is independent of PPARα activation in livers of newborn 129 and SW/129 Pex2(-/-) mice. Two-week-old wild-type mice treated with the peroxisome proliferator WY-14,643 show strong induction of PPARα-regulated genes and decreased expression of SREBP-2 and its target genes, further demonstrating that SREBP-2 pathway induction is not dependent on PPARα activation. Lastly, there is no activation of either SREBP-2 or ER stress pathways in kidney and lung of newborn Pex2(-/-) mice, suggesting a parallel induction of these pathways in peroxisome-deficient mice. These findings establish novel associations between SREBP-2, ER stress and PPARα pathway inductions.

Peroxisome deficiency causes a complex phenotype because of hepatic SREBP/Insig dysregulation associated with endoplasmic reticulum stress

Regulation of hepatic cholesterol biosynthesis, lipogenesis, and insulin signaling intersect at the transcriptional level by control of SREBP and Insig genes. We previously demonstrated that peroxisome-deficient PEX2-/- mice activate SREBP-2 pathways but are unable to maintain normal cholesterol homeostasis. In this study, we demonstrate that oral bile acid treatment normalized hepatic and plasma cholesterol levels and hepatic cholesterol synthesis in early postnatal PEX2 mutants, but SREBP-2 and its target gene expressions remained increased. SREBP-2 pathway induction was also observed in neonatal and longer surviving PEX2 mutants, where hepatic cholesterol levels were normal. Abnormal expression patterns for SREBP-1c and Insig-2a, and novel regulation of Insig-2b, further demonstrate that peroxisome deficiency widely affects the regulation of related metabolic pathways. We have provided the first demonstration that peroxisome deficiency activates hepatic endoplasmic reticulum (ER) stress pathways, especially the integrated stress response mediated by PERK and ATF4 signaling. Our studies suggest a mechanism whereby ER stress leads to dysregulation of the endogenous sterol response mechanism and concordantly activates oxidative stress pathways. Several metabolic derangements in peroxisome-deficient PEX2-/- liver are likely to trigger ER stress, including perturbed flux of mevalonate metabolites, altered bile acid homeostasis, changes in fatty acid levels and composition, and oxidative stress.

Differential expression of peroxisomal matrix and membrane proteins during postnatal development of mouse brain

In peroxisomal biogenesis disorders, serious neurological abnormalities can be observed in the patients and the respective knockout mouse models. As a prerequisite for a better understanding of the relationship between the absence of peroxisomes and the observed neuropathology, knowledge of the regional and cell-type specific distribution of peroxisomal proteins in mouse brain is necessary. Therefore, we investigated the expression of distinct peroxins, peroxisomal membrane and matrix proteins (e.g. Pex5p, Pex14p, Pex13p, PMP70, catalase, peroxisomal thiolase, Acox1, "SKL"-PTS1 proteins) by indirect immunofluorescence 1) in primary cultures of the medial neocortex, hippocampus, and cerebellum of newborn mice and 2) in paraffin sections of mouse brain of different ages (newborn-adult). Quantitative analysis revealed a comparable abundance (number/microm(2)) of peroxisomes in cultured neurons and astrocytes of all three brain regions. In contrast, catalase immunoreactivity was higher in cultured astrocytes than in neurons. In mouse brain tissue, the abundance of peroxisomes decreased by half during postnatal development, also exhibiting prominent differences between distinct brain regions and cell types. Catalase protein levels in neuronal peroxisomes, however, decreased much more strongly in the neocortex, CA1-3 areas of the hippocampus, dentate gyrus, cerebellar nuclei, and cerebellar cortex but remained high in Bergmann glia and other astrocytes, epithelial cells of the choroid plexus, and ependyma. Similar age-dependent changes were found for thiolase and Acox1 protein levels. Developmental changes were confirmed by Western blot analysis using enriched peroxisomal and cytosolic fractions of the brain tissue as well as by measurement of catalase activity.

Localization of the pre-squalene segment of the isoprenoid biosynthetic pathway in mammalian peroxisomes

Previous studies have indicated that the early steps in the isoprenoid/cholesterol biosynthetic pathway occur in peroxisomes. However, the role of peroxisomes in cholesterol biosynthesis has recently been questioned in several reports concluding that three of the peroxisomal cholesterol biosynthetic enzymes, namely mevalonate kinase, phosphomevalonate kinase, and mevalonate diphosphate decarboxylase, do not localize to peroxisomes in human cells even though they contain consensus peroxisomal targeting signals. We re-investigated the subcellular localization of the cholesterol biosynthetic enzymes of the pre-squalene segment in human cells by using new stable isotopic techniques and data computations with isotopomer spectral analysis, in combination with immunofluorescence and cell permeabilization techniques. Our present findings clearly show and confirm previous studies that the pre-squalene segment of the cholesterol biosynthetic pathway is localized to peroxisomes. In addition, our data are consistent with the hypothesis that acetyl-CoA derived from peroxisomal beta-oxidation of very long-chain fatty acids and medium-chain dicarboxylic acids is preferentially channeled to cholesterol synthesis inside the peroxisomes without mixing with the cytosolic acetyl-CoA pool.

The hypolipidemic compound cetaben induces changes in Golgi morphology and vesicle movement

The human hepatoma cell line HepG2 was used to study the effect of cetaben, a non-fibrate hypolipidemic drug, on cell morphology and vesicle distribution. Cetaben treatment correlated with a fragmentation and/or condensation of Golgi cisternae and the appearance of large electron-lucent vesicles. The Golgi apparatus, demonstrated, for example, by fluorescence-lectin histochemistry, was fragmented after cetaben treatment. The lectin-positive remnants were dispersed throughout the cytoplasm, but with a preference for being transported to tips of cells. However, microtubules and the intermediate filaments as well as the actin microfilaments were unchanged after cetaben treatment indicating that changes in Golgi morphology are not caused by alterations in the cytoskeleton. Cetaben decreases the cholesterol content due to inhibition of cholesterol biosynthesis. Changes in the intracellular cholesterol content are known to influence the intracellular vesicle distribution and are most likely responsible for cetaben-induced Golgi alterations, as depletion of cellular cholesterol by starvation or lovastatin and/or cyclodextrin treatment resulted in a similar redistribution of Golgi-derived wheat germ agglutinin vesicles. These lectin-stained vesicles colocalized with lysosomal marker proteins such as Limp-1 and Lamp-2, but not with the early endosomal markers Rab5 and EEA1. Upon removal of cetaben the lectin- and Limp-1/Lamp-2-costained vesicles dissociated and were transported back to the perinuclear region. Thus, cetaben-induced changes such as fragmentation of the Golgi apparatus and the dispersion of lysosomes away from their juxtanuclear location were reversible.

Disturbed cholesterol homeostasis in a peroxisome-deficient PEX2 knockout mouse model

We evaluated the major pathways of cholesterol regulation in the peroxisome-deficient PEX2(-/-) mouse, a model for Zellweger syndrome. Zellweger syndrome is a lethal inherited disorder characterized by severe defects in peroxisome biogenesis and peroxisomal protein import. Compared with wild-type mice, PEX2(-/-) mice have decreased total and high-density lipoprotein cholesterol levels in plasma. Hepatic expression of the SREBP-2 gene is increased 2.5-fold in PEX2(-/-) mice and is associated with increased activities and increased protein and expression levels of SREBP-2-regulated cholesterol biosynthetic enzymes. However, the upregulated cholesterogenic enzymes appear to function with altered efficiency, associated with the loss of peroxisomal compartmentalization. The rate of cholesterol biosynthesis in 7- to 9-day-old PEX2(-/-) mice is markedly increased in most tissues, except in the brain and kidneys, where it is reduced. While the cholesterol content of most tissues is normal in PEX2(-/-) mice, in the knockout mouse liver it is decreased by 40% relative to that in control mice. The classic pathway of bile acid biosynthesis is downregulated in PEX2(-/-) mice. However, expression of CYP27A1, the rate-determining enzyme in the alternate pathway of bile acid synthesis, is upregulated threefold in the PEX2(-/-) mouse liver. The expression of hepatic ATP-binding cassette (ABC) transporters (ABCA1 and ABCG1) involved in cholesterol efflux is not affected in PEX2(-/-) mice. These data illustrate the diversity in cholesterol regulatory responses among different organs in postnatal peroxisome-deficient mice and demonstrate that peroxisomes are critical for maintaining cholesterol homeostasis in the neonatal mouse.

Central role of peroxisomes in isoprenoid biosynthesis

Peroxisomes contain enzymes catalyzing a number of indispensable metabolic functions mainly related to lipid metabolism. The importance of peroxisomes in man is stressed by the existence of genetic disorders in which the biogenesis of the organelle is defective, leading to complex developmental and metabolic phenotypes. The purpose of this review is to emphasize some of the recent findings related to the localization of cholesterol biosynthetic enzymes in peroxisomes and to discuss the impairment of cholesterol biosynthesis in peroxisomal deficiency diseases.

Effects of androgens on T and B lymphocyte development

The sexually dimorphic nature of normal immune responses and the remarkably higher incidence of autoimmune diseases in females have suggested a role for gonadal steroid hormones as modulators of immune system function. We have investigated the effects of androgens on the development of lymphocytes in the thymus and bone marrow. Expression of the androgen receptor, the ligand-activated transcription factor that mediates hormone actions, has been documented in lymphoid and nonlymphoid cells of thymus and bone marrow, but not in mature peripheral lymphocytes. This expression pattern suggests that the major impact of androgens must be on the developmental maturation of T and B lymphocytes rather than on the mature effector cells. Recent experiments have explored whether developing lymphoid precursors are the direct targets of androgen action or whether supporting cells, such as thymic epithelial cells and bone marrow stromal cells, are required for the receptor-mediated effects of androgens on lymphoid cell development. Bone marrow transplantation techniques using an androgen-resistant mouse strain permit the creation of chimeric mice with androgen receptor-defective lymphoid or epithelial/stromal cellular compartments. Hormonal manipulation experiments in these chimeric animals have suggested that thymic epithelial cells and bone marrow stromal cells are mediators of androgenic effects on immature lymphocytes. The long-range goal of these studies is to understand the basis for the disproportionate occurrence of autoimmune diseases in females.

Bone marrow stromal cells mediate androgenic suppression of B lymphocyte development

Castration of normal male mice induces expansion of the bone marrow B cell population, an effect that can be reversed by androgen replacement. We employed in vitro cultures and two in vivo models to investigate whether androgens exert these effects directly on marrow lymphoid precursors or whether actions on marrow stromal elements are required. Immature B cells from normal mouse bone marrow were not responsive to the suppressive effect of androgens unless they were cocultured with marrow stromal cells or with supernatants from androgen-treated stromal cells, suggesting that the androgen effects are exerted through marrow stromal elements by production of a diffusible mediator. Further experiments revealed that bone marrow stromal cells produced TGF-beta in response to dihydrotestosterone (DHT), and neutralization of TGF-beta in the DHT-treated stromal cells reversed the suppressive effects. The stromal cell requirement for androgen-mediated effects was confirmed in vivo by experiments using chimeric animals created by bone marrow transplantation in which androgen receptor expression was restricted to either the stromal or lymphoid cells of the bone marrow. Androgens only affected B cell development in chimeric mice with androgen-sensitive stromal cells. These experiments suggest that effects of androgens on developing B cells are mediated through androgen receptors in bone marrow stromal cells. TGF-beta is a candidate mediator for these hormonal effects.

Purification of brain peroxisomes and localization of 3-hydroxy-3-methylglutaryl coenzyme A reductase

At least three different subcellular compartments, including peroxisomes, are involved in cholesterol biosynthesis. Because proper CNS development depends on de novo cholesterol biosynthesis, peroxisomes must play a critical functional role in this process. Surprisingly, no information is available on the peroxisomal isoprenoid/cholesterol biosynthesis pathway in normal brain tissue or on the compartmentalization of isoprene metabolism in the CNS. This has been due mainly to the lack of a well-defined isolation procedure for brain tissue, and also to the presence of myelin in brain tissue, which results in significant contamination of subcellular fractions. As a first step in characterizing the peroxisomal isoprenoid pathway in the CNS, we have established a purification procedure to isolate peroxisomes and other cellular organelles from the brain stem, cerebellum and spinal cord of the mouse brain. We demonstrate by use of marker enzymes and immunoblotting with antibodies against organelle specific proteins that the isolated peroxisomes are highly purified and well separated from the ER and mitochondria, and are free of myelin contamination. The isolated peroxisomal fraction was purified at least 40-fold over the original homogenate. In addition, we show by analytical subcellular fractionation and immunoelectron microscopy that HMG-CoA reductase protein and activity are localized both in the ER and peroxisomes in the CNS.

Alterations in the regulation of androgen-sensitive Cyp 4a monooxygenases cause hypertension

Hypertension is a leading cause of cardiovascular, cerebral, and renal disease morbidity and mortality. Here we show that disruption of the Cyp 4a14 gene causes hypertension, which is, like most human hypertension, more severe in males. Male Cyp 4a14 (-/-) mice show increases in plasma androgens, kidney Cyp 4a12 expression, and the formation of prohypertensive 20-hydroxyarachidonate. Castration normalizes the blood pressure of Cyp 4a14 (-/-) mice and minimizes Cyp 4a12 expression and arachidonate omega-hydroxylation. Androgen replacement restores hypertensive phenotype, Cyp 4a12 expression, and 20-hydroxy-arachidonate formation. We conclude that the androgen-mediated regulation of Cyp 4a arachidonate monooxygenases is an important component of the renal mechanisms that control systemic blood pressures. These results provide direct evidence for a role of Cyp 4a isoforms in cardiovascular physiology, establish Cyp 4a14 (-/-) mice as a monogenic model for the study of cause/effect relationships between blood pressure, sex hormones, and P450 omega-hydroxylases, and suggest the human CYP 4A homologues as candidate genes for the analysis of the genetic and molecular basis of human hypertension.

Androgen receptors in thymic epithelium modulate thymus size and thymocyte development

Castration of normal male rodents results in significant enlargement of the thymus, and androgen replacement reverses these changes. Androgen-resistant testicular feminization (Tfm) mice also show significant thymus enlargement, which suggests that these changes are mediated by the androgen receptor (AR). The cellular targets of androgen action in the thymus are not known, but may include the lymphoid cells (thymocytes) as well as nonlymphoid epithelial cells, both of which have been believed to express AR. In the present study immunohistochemical analysis and hormone binding assays were used to demonstrate the presence of AR in thymic epithelial cells. The physiological significance of this epithelial cell AR expression was defined by further studies performed in vivo using chimeric mice, produced by bone marrow transplantation, in which AR expression was limited to either lymphoid or epithelial components of the thymus. Chimeric C57 mice engrafted with Tfm bone marrow cells (AR(+) epithelium and AR(-) thymocytes) had thymuses of normal size and showed the normal involutional response to androgens, whereas chimeric Tfm mice engrafted with C57 bone marrow cells (AR(-) epithelium and AR(+) thymocytes) showed thymus enlargement and androgen insensitivity. Furthermore, phenotypic analyses of lymphocytes in mice with AR(-) thymic epithelium showed abrogation of the normal responses to androgens. These data suggest that AR expressed by thymic epithelium are important modulators of thymocyte development.

Function of a truncated glucocorticoid receptor form at a negative glucocorticoid response element in the proopiomelanocortin gene

ACTH-producing tumors of nonpituitary origin characteristically exhibit insensitivity to the negative feedback effects of glucocorticoids. In the DMS-79 cell line derived from an ACTH-producing small cell lung cancer we have previously identified an aberrantly spliced glucocorticoid receptor (GRDelta) that lacks a ligand-binding domain. We examined the interactions of this truncated form of GR with the proximal human proopiomelanocortin (POMC) promoter. In electrophoretic mobility shift assays GRDelta bound to the negative glucocorticoid response element (nGRE) at position -78 to -50 in the human POMC promoter. Nur77, an orphan nuclear receptor that exerts positive regulatory effects on the POMC gene is also known to bind to this DNA element. The functional properties of GR and GRDelta binding to this DNA element were examined in transient transfection experiments in murine AtT-20 corticotroph tumor cells. Reporter gene expression under the control of proximal POMC promoter elements was stimulated by addition of forskolin to the culture medium or by transfection with expression constructs for human Nak1, the human homologue of Nur77. Treatment of transfected cells with dexamethasone resulted in suppression of forskolin- or Nak1-stimulated POMC-reporter gene expression in the presence of co-transfected GR but not with GRDelta. The experiments indicate that in the human POMC promoter GRDelta is capable of binding to the nGRE but cannot effect trans-repression of POMC-reporter gene expression.

Expression of 11beta-hydroxysteroid dehydrogenase type 2 in an ACTH-producing small cell lung cancer

Non-pituitary tumors that produce adrenocorticotropic hormone (ACTH) exhibit resistance to the normal feedback effects of glucocorticoids on proopiomelanocortin (POMC) gene expression. This glucocorticoid resistance is typically complete, although some tumors show only relative glucocorticoid resistance in the clinical setting. The molecular mechanisms responsible for these clinical pathophysiologic observations are unknown, but might include glucocorticoid receptor defects or aberrant expression of enzymes or transporters that exclude glucocorticoids from access to their intracellular receptors. We examined whether ACTH-producing non-pituitary tumor cells might express 11beta-hydroxysteroid dehydrogenase (11beta-HSD), the principal 'gatekeeper' enzyme known to metabolize glucocorticoids. 11Beta-HSD mRNA and enzyme activity were assessed in DMS-79 cells, a line derived from an ACTH-producing small cell lung cancer. RT-PCR studies showed expression of mRNA encoding 11beta-HSD2 but not 11beta-HSD1 in DMS-79 cells. Control human fibroblasts expressed predominantly 11beta-HSD1 but also had detectable 11beta-HSD2 mRNA, while HepG2 hepatoma cells also expressed only 11beta-HSD2 mRNA. Whole cell assays in DMS-79 cells revealed 11beta-HSD activity with a Km for cortisol of 26.1 +/- 9.0 nM and Vmax of 57.0 +/- 5.9 pmol/h/mg protein. HepG2 cells expressed a similar high affinity enzyme activity, while control fibroblasts expressed 11beta-HSD activity with a Km for cortisol of 652 nM. Conversion of cortisol to cortisone in DMS-79 cells was inhibited to 7% of baseline by addition of 10 microM glycyrrhetinic acid. Dexamethasone (20 nM) was converted to a single product in DMS-79 cells at a rate of 17.2 pmol/h/mg protein; this activity was also inhibited by glycyrrhetinic acid. We conclude that DMS-79 cells express 11beta-HSD2. While DMS-79 cells harbor additional defects in glucocorticoid signaling, these data suggest that expression of 11beta-HSD2 might contribute to the development of the glucocorticoid-resistant phenotype of some ACTH-producing tumors.

An ACTH-producing small cell lung cancer expresses aberrant glucocorticoid receptor transcripts from a normal gene

ACTH production by non-pituitary tumors is generally not suppressible by exogenous glucocorticoid administration. We had postulated that defects in the glucocorticoid receptor (GR) signaling system might be responsible for this apparent glucocorticoid resistance and had previously demonstrated that DMS-79 cells, derived from an ectopic ACTH-producing tumor, express an abnormal GR mRNA. In this DMS-79 cell GR the sequence normally derived from exons 8 and 9 is replaced by sequence unmatched in the DNA databases. The protein encoded by this mRNA lacks the steroid-binding domain and does not function as a ligand-activated transcription factor. In the present work, we sought to identify the origin of the novel GR mRNA sequence. Southern blot analysis of DMS-79 genomic DNA showed no major structural alteration of the GR gene. Southern blotting of cosmid clones of the normal GR gene revealed that the novel DMS-79 GR mRNA sequence is derived from intron G, between exons 7 and 8. No splice site mutations were found in PCR-amplified DMS-79 DNA fragments surrounding the downstream splice junctions. Further sequencing indicated that the aberrant GR transcript appears to be generated by use of a consensus cleavage/polyadenylation signal found 3650 base pairs into the normal intron G. We conclude that abnormal GR pre-mRNA processing rather than a GR gene mutation confers glucocorticoid resistance on DMS-79 cells.

Androgens accelerate thymocyte apoptosis

Mechanisms of androgen-induced thymic involution are largely undefined. We have found that significant decreases in thymic size occur 2-4 h after a dose of testosterone is administered to castrated male mice. This rapid rate of change suggests a role for androgen-induced apoptosis in modulating the size and composition of the thymus. Using thymic organ cultures to define these effects of androgens, we found that dihydrotestosterone treatment of thymus tissues from females or from castrated males results in enhancement of thymocyte apoptosis. Intact (androgen-replete) or testicular feminization, Tfm/Y (androgen-resistant) mice failed to show apoptotic change with androgen treatment, although the apoptotic response to glucocorticoids was present, suggesting a requirement for a functional androgen receptor. Acceleration of thymocyte apoptosis by androgens may mediate processes of thymocyte selection, with the potential to impart gender-specific characteristics on the peripheral T cell repertoire.

Androgens alter B cell development in normal male mice

Castration of normal male mice leads to splenic enlargement and expansion of the B cell population. Since the spleen does not express receptors for androgens, these changes are most likely mediated by effects of androgens on other target organs. Two potential sites of androgen-mediated effects on B cells are evaluated in these studies: thymus and bone marrow. We first confirmed other findings indicating that castration of normal male mice results in expansion in the numbers of bone marrow B cells and then extended these observations by showing that these changes were reversible following androgen replacement. B cell expansion in castrate marrow and spleen was not altered by prior thymectomy, suggesting that thymic androgen receptors are not involved in the observed effects. Androgen receptors were found to be present in both immature B cells and marrow stromal cells by immunoblotting and ligand binding assays. The results suggest a direct modulatory role for androgens on B cells within the bone marrow compartment.

Schistosoma mansoni: susceptibility differences between male and female mice can be mediated by testosterone during early infection

In murine Schistosoma mansoni infections, fewer adult worms develop in male than in female mice infected with the same number of cercariae. To evaluate a potential role for testosterone in this phenomenon, testosterone levels were manipulated in groups of CBA/J mice that were then infected and monitored for survival rates, worm burdens, organomegaly, and egg production. By 16 weeks of infection, more than 80% of mice in groups with low levels of testosterone (untreated females, castrated males, or carrier-treated castrates) were dead, while less than 40% of those in groups with high levels of testosterone (sham-castrated males, testosterone-treated castrates, or testosterone-treated female mice) succumbed to infection. The mean number of worms recovered from mice in the low testosterone level groups was comparable among groups, and significantly greater than that from those in high-testosterone-level groups. The degree of organomegaly observed correlated strongly with worm burden, but the number of hepatic eggs per female worm did not differ significantly between groups. When male mice were castrated or sham-castrated 5 weeks after S. mansoni infection, no significant differences in host survival occurred. Furthermore, female mice treated with testosterone demonstrated reduced worm burdens if the testosterone was given 10 days prior to infection but not if the testosterone was given 10 days or 5 weeks after infection. Thus, the host sex bias observed in parallel-infected male and female mice appears to be related to the presence of male gonadal tissue or testosterone early in infection, during the development of immature schistosomules.

Case report: testosterone treatment of systemic lupus erythematosus in a patient with Klinefelter's syndrome

Systemic lupus erythematosus occurs with much greater frequency in females than in males, and in some reports, researchers suggested that treatment with androgenic hormones might have therapeutic effects in this disease. The authors report a case of systemic lupus erythematosus in a hypogonadal male with Klinefelter's syndrome who was treated with testosterone in doses sufficient to normalize the serum level of this hormone to the adult male range. Hematologic and serologic abnormalities, including elevated levels of anti-DNA antibodies and depressed complement levels, returned to normal within 9 months of increasing the testosterone dose. The findings in this patient indicate that androgenic steroids can exert significant effects on immune parameters, and suggest that effects of androgens on the immune system may contribute to the sexual dimorphism of autoimmune disease.

Glucocorticoid receptor structure and function in an adrenocorticotropin-secreting small cell lung cancer

ACTH secretion by tumors of nonpituitary origin is characteristically resistant to negative feedback regulation by glucocorticoids. One possible mechanism for the phenomenon could be a structural defect in the intracellular glucocorticoid receptor (GR). We studied the GR in DMS-79 cells derived from a human ACTH-secreting small cell lung cancer. Compared with control cells, DMS-79 cells were found to have greatly diminished GR ligand-binding activity and immunoreactive 94-kilodalton (kDa) GR content. Northern blot analysis revealed expression of GR transcripts that appeared to be slightly larger than those in control cells. A DMS-79 cell GR cDNA was cloned by reverse transcription/polymerase chain reaction amplification of mRNA using primers specific for full-length normal GR. The derived sequence of this full-length GR differed from the reported sequence by a single altered codon (G to A; Asn to Ser at codon 363) outside the steroid-binding domain. This N363S DMS-79 GR functioned normally to activate a target gene [mouse mammary tumor virus-chloramphenicol acetyl transferase (MMTV-CAT)] in transient transfection experiments in COS cells. Evidence for expression of a second type of GR mRNA was obtained by screening a DMS-79 cell cDNA library. This GR cDNA contained normal GR sequence up to nucleotide 2155, corresponding exactly to the end of exon 7 in the normal GR gene. The sequence appended to the GR sequences was not matched by any known sequence in DNA databases and included an in-frame termination codon after only 6 bases. The predicted truncated GR protein product (GR delta) has a mol wt of 73,740 and lacks most of the ligand-binding domain. Transient transfection of the GR delta form into COS cells did not reveal any dominant negative effect on the function of a cotransfected normal GR.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunochemical and flow cytometric analysis of androgen receptor expression in thymocytes

A variety of evidence suggests that the cells of the immune system are targets for the actions of gonadal steroids. Experiments in both normal animals and in autoimmune disease models have established that androgens exert immunomodulatory effects at the level of the thymus. We have attempted to define precisely the potential target cells for androgen action in the thymus using recently developed antibodies to the androgen receptor. We report here that these antibodies reveal AR expression in all classes of thymocytes defined by surface markers CD4 and CD8. The highest levels of AR expression were observed in the CD4-CD8+ and CD4-CD8- subsets that include the most immature cells. These experiments establish that thymocytes are potential targets for direct actions of androgens. The data further suggest AR expression in thymocytes may be developmentally regulated in these cells, and that androgen effects early in the process of thymocyte selection may contribute to the sexual dimorphism of immune responsiveness.

Castration alters peripheral immune function in normal male mice

While it is generally recognized that females show enhanced cell-mediated and antibody responses to antigenic stimulation, the physiological basis for this observed sexual dimorphism of the immune response is not well understood. We report here studies on the effects of androgen deficiency on the peripheral immune system. Intact male mice were compared to animals castrated 3-4 months previously. Phenotypic characterization of thymocyte and lymphocyte subpopulations was carried out using dual-colour flow cytometry. In vitro production by spleen cells of interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma), and levels of total immunoglobulin and autoreactive antibodies was measured by specific immunoassays. In addition to thymic hypertrophy, castrated animals showed significant splenic enlargement, which was largely owing to expansion of the B-cell population. The castrated spleens contained relatively fewer mature T cells than intact controls (P < or = 0.001), but culture supernatants from these spleen cells contained higher levels of IL-2 and IFN-gamma than control cultures (P < 0.04). Levels of in vitro antibody synthesis (IgM, IgG, IgA) were not higher in castrated animals compared to controls, but the castrate spleen cell cultures showed increased levels of production of two autoreactive antibodies, anti-IgG (rheumatoid factor) and anti-thyroglobulin. These data suggest that androgen deprivation results in a relative decrease in the number of mature peripheral T cells, but those which reach the spleen have functional characteristics suggestive of enhanced activation. Dysregulation in the B-cell compartment may be the result of altered effects of T-cell-mediated control.

Induction of immature thymocyte proliferation after castration of normal male mice

The physiological basis and immunological significance of thymic enlargement in castrate male animals is not known. We used normal male C57 Bl/6 mice to examine the contribution of in situ thymocyte proliferation to castration-induced enlargement of the thymus. Animals castrated at 8-10 weeks of age were compared to normal intact males. Thymocytes were examined 4-120 days after castration using flow cytometry to determine DNA content and thus the number of cells in active phases of the cell cycle. These properties were examined in unseparated thymocytes and in phenotypic subpopulations defined by expression of CD3, CD4, and CD8. For thymocytes obtained from intact control glands, a mean of 11.0 +/- 1.0% were in active phases of the cell cycle. The percentage of cycling thymocytes was increased to a mean of 22.5 +/- 1.9% in the week after castration (P < 0.001). This change occurred in the absence of significant thymic enlargement. At 8-10 days after castration, thymic weight increased abruptly to a new steady state which was double that of intact controls (78.0 +/- 4.1 vs. 39.1 +/- 2.6 mg; P < 0.001). In these enlarged glands, only 9.9 +/- 0.8% of cells were cycling, which was not significantly different than controls (P > 0.3). Proliferating cells identified in fixed thymus tissue sections after in vivo administration of bromodeoxyuridine were located in the subcapsular cortex and medulla. Analyses of thymocyte subpopulations indicated that most cycling cells had immature phenotypes (CD4+CD8+, CD4-CD8+, and CD3lo or CD3-). Castrate glands studied in the steady state period 8-120 days after surgery contained significantly fewer CD3+ cells than intact controls (P < or = 0.045). The findings suggest an intrathymic role for androgens in affecting generation of the mature T cell repertoire.

Determination of the lethal dose of dexamethasone for early passage in vitro human glioblastoma cell cultures

Previous investigators have supported the idea that glucocorticoids may be oncolytic. In this study, the percentage of cell death in two human glioblastoma cell cultures was related to the concentration of dexamethasone that was administered. It was determined that for Cell line 1, the median lethal dose was approximately 500-800 micrograms/ml and the completely lethal dose was about 900-1000 micrograms/ml; the 3H-thymidine uptake to approximate the mitotic rate was 16,607 cpm, and the dexamethasone receptor activity was 228 fmol/mg protein. The median lethal dose and completely lethal dose for Cell line 2 was approximately 500-600 micrograms/ml and 700-1000 micrograms/ml, respectively; the 3H-thymidine uptake was 8402 cpm, and the dexamethasone receptor activity was 137 fmol/mg protein. These lethal concentrations of dexamethasone are probably higher than can be tolerated by systemic delivery. However, it remains to be seen whether the interstitial administration of dexamethasone could achieve local concentrations resulting in the oncolysis of malignant gliomas. The clinical significance of these findings will depend on the local tolerance of normal brain parenchyma to very high doses of dexamethasone. A review of some of the literature is included.

Testosterone induces expression of transforming growth factor-beta 1 in the murine thymus

Castration of adult male mice results in enlargement of the thymus and diminution of peripheral suppressor T cell function. Replacement therapy with physiologic doses of androgens reverses these phenomena. Although the mediators involved are unknown, these effects of androgens on the thymus and peripheral immune system are reminiscent of those reported for transforming growth factor-beta (TGF-beta 1). We examined expression of TGF-beta 1 mRNA and bioactive protein in thymuses from castrate and androgen-replaced animals. Steady-state levels of thymic TGF-beta 1 mRNA fell slightly after castration, but rose 2.3-fold after testosterone replacement. Bioactive TGF-beta 1 production by cultured thymic explants also fell following castration to approx. 50% of the levels observed in intact animals. Following 1 week of testosterone replacement in castrate animals, TGF-beta 1 bioactivity produced in culture was restored to levels indistinguishable from those observed with explants from intact animals. Reverse transcription/polymerase chain reaction amplification of RNA revealed that thymocytes are a source of the androgen-modulated TGF-beta 1. These results suggest that TGF-beta 1 may mediate effects of androgens on the immune system.

An androgenic affinity ligand covalently binds to cytosolic aldehyde dehydrogenase from human genital skin fibroblasts

A 56 kDa protein expressed in human genital skin fibroblasts was first identified by independent laboratories on the basis of its specific expression in androgen target cells and its ability to covalently bind androgenic affinity ligands. Recently, immunoscreening of a cDNA library with antisera directed against this protein resulted in the isolation of a partial cDNA clone identical to human cytosolic aldehyde dehydrogenase (ALDH1). We report here the preparation of a full-length cDNA encoding ALDH1 from human genital fibroblasts. Translation of the encoded protein in a cell-free system yields a 56 kDa product that can be covalently radiolabeled with [3H]dihydrotestosterone 17 beta-bromoacetate (DHT-BA). Expression of the full-length clone in mammalian cells also results in expression of a 56 kDa DHT-BA binding protein. The covalent binding of DHT-BA by ALDH1 is an intrinsic property of the enzyme and is not dependent on androgen receptor expression.