Harald Esterbauer

Oxidative damage in multiple sclerosis lesions

Multiple sclerosis is a chronic inflammatory disease of the central nervous system, associated with demyelination and neurodegeneration. The mechanisms of tissue injury are currently poorly understood, but recent data suggest that mitochondrial injury may play an important role in this process. Since mitochondrial injury can be triggered by reactive oxygen and nitric oxide species, we analysed by immunocytochemistry the presence and cellular location of oxidized lipids and oxidized DNA in lesions and in normal-appearing white matter of 30 patients with multiple sclerosis and 24 control patients without neurological disease or brain lesions. As reported before in biochemical studies, oxidized lipids and DNA were highly enriched in active multiple sclerosis plaques, predominantly in areas that are defined as initial or ‘prephagocytic’ lesions. Oxidized DNA was mainly seen in oligodendrocyte nuclei, which in part showed signs of apoptosis. In addition, a small number of reactive astrocytes revealed nuclear expression of 8-hydroxy-d-guanosine. Similarly, lipid peroxidation-derived structures (malondialdehyde and oxidized phospholipid epitopes) were seen in the cytoplasm of oligodendrocytes and some astrocytes. In addition, oxidized phospholipids were massively accumulated in a fraction of axonal spheroids with disturbed fast axonal transport as well as in neurons within grey matter lesions. Neurons stained for oxidized phospholipids frequently revealed signs of degeneration with fragmentation of their dendritic processes. The extent of lipid and DNA oxidation correlated significantly with inflammation, determined by the number of CD3 positive T cells and human leucocyte antigen-D expressing macrophages and microglia in the lesions. Our data suggest profound oxidative injury of oligodendrocytes and neurons to be associated with active demyelination and axonal or neuronal injury in multiple sclerosis.

Targeted deletion of AIF decreases mitochondrial oxidative phosphorylation and protects from obesity and diabetes

Type-2 diabetes results from the development of insulin resistance and a concomitant impairment of insulin secretion. Recent studies place altered mitochondrial oxidative phosphorylation (OxPhos) as an underlying genetic element of insulin resistance. However, the causative or compensatory nature of these OxPhos changes has yet to be proven. Here, we show that muscle- and liver-specific AIF ablation in mice initiates a pattern of OxPhos deficiency closely mimicking that of human insulin resistance, and contrary to current expectations, results in increased glucose tolerance, reduced fat mass, and increased insulin sensitivity. These results are maintained upon high-fat feeding and in both genetic mosaic and ubiquitous OxPhos-deficient mutants. Importantly, the effects of AIF on glucose metabolism are acutely inducible and reversible. These findings establish that tissue-specific as well as global OxPhos defects in mice can counteract the development of insulin resistance, diabetes, and obesity.

A common polymorphism in the promoter of UCP2 is associated with decreased risk of obesity in middle-aged humans

Obesity is the most common nutritional disorder in Western society. Uncoupling protein-2 (UCP2) is a recently identified member of the mitochondrial transporter superfamily that is expressed in many tissues, including adipose tissue. Like its close relatives UCP1 and UCP3, UCP2 uncouples proton entry in the mitochondrial matrix from ATP synthesis and is therefore a candidate gene for obesity. We show here that a common G/A polymorphism in the UCP2 promoter region is associated with enhanced adipose tissue mRNA expression in vivo and results in increased transcription of a reporter gene in the human adipocyte cell line PAZ-6. In analyzing 340 obese and 256 never-obese middle-aged subjects, we found a modest but significant reduction in obesity prevalence associated with the less-common allele. We confirmed this association in a population-based sample of 791 middle-aged subjects from the same geographic area. Despite its modest effect, but because of its high frequency (∼63%), the more-common risk allele conferred a relatively large population-attributable risk accounting for 15% of the obesity in the population studied.

Drosophila Genome-wide Obesity Screen Reveals Hedgehog as a Determinant of Brown versus White Adipose Cell Fate

Over 1 billion people are estimated to be overweight, placing them at risk for diabetes, cardiovascular disease, and cancer. We performed a systems-level genetic dissection of adiposity regulation using genome-wide RNAi screening in adult Drosophila. As a follow-up, the resulting approximately 500 candidate obesity genes were functionally classified using muscle-, oenocyte-, fat-body-, and neuronal-specific knockdown in vivo and revealed hedgehog signaling as the top-scoring fat-body-specific pathway. To extrapolate these findings into mammals, we generated fat-specific hedgehog-activation mutant mice. Intriguingly, these mice displayed near total loss of white, but not brown, fat compartments. Mechanistically, activation of hedgehog signaling irreversibly blocked differentiation of white adipocytes through direct, coordinate modulation of early adipogenic factors. These findings identify a role for hedgehog signaling in white/brown adipocyte determination and link in vivo RNAi-based scanning of the Drosophila genome to regulation of adipocyte cell fate in mammals.

The sedoheptulose kinase CARKL directs macrophage polarization through control of glucose metabolism.

Summary Immune cells are somewhat unique in that activation responses can alter quantitative phenotypes upwards of 100,000-fold. To date little is known about the metabolic adaptations necessary to mount such dramatic phenotypic shifts. Screening for novel regulators of macrophage activation, we found nonprotein kinases of glucose metabolism among the most enriched classes of candidate immune modulators. We find that one of these, the carbohydrate kinase-like protein CARKL, is rapidly downregulated in vitro and in vivo upon LPS stimulation in both mice and humans. Interestingly, CARKL catalyzes an orphan reaction in the pentose phosphate pathway, refocusing cellular metabolism to a high-redox state upon physiological or artificial downregulation. We find that CARKL-dependent metabolic reprogramming is required for proper M1- and M2-like macrophage polarization and uncover a rate-limiting requirement for appropriate glucose flux in macrophage polarization.

Activation of the BCL2 Promoter in Response to Hedgehog/GLI Signal Transduction Is Predominantly Mediated by GLI2

Aberrant activation of the Hedgehog (HH)/GLI signaling pathway has been implicated in the development of basal cell carcinoma (BCC). The zinc finger transcription factors GLI1 and GLI2 are considered mediators of the HH signal in epidermal cells, although their tumorigenic nature and their relative contribution to tumorigenesis are only poorly understood. To shed light on the respective role of these transcription factors in epidermal neoplasia, we screened for genes preferentially regulated either by GLI1 or GLI2 in human epidermal cells. We show here that expression of the key antiapoptotic factor BCL2 is predominantly activated by GLI2 compared with GLI1. Detailed promoter analysis and gel shift assays identified three GLI binding sites in the human BCL2 cis-regulatory region. We found that one of these binding sites is critical for conferring GLI2-specific activation of the human BCL2 promoter and that the selective induction of BCL2 expression depends on the zinc finger DNA binding domain of GLI2. In vivo, GLI2 and BCL2 were coexpressed in the outer root sheath of hair follicles and BCC and in plasma cells that infiltrated BCC tumor islands. On the basis of the latter observation, we analyzed plasma cell-derived tumors and found strong expression of GLI2 and BCL2 in neoplastic cells of plasmacytoma patients, implicating HH/GLI signaling in the development of plasma cell-derived malignancies. The results reveal a central role for GLI2 in activating the prosurvival factor BCL2, which may represent an important mechanism in the development or maintenance of cancers associated with inappropriate HH signaling.

Stat3 Is a Negative Regulator of Intestinal Tumor Progression in ApcMin Mice

BACKGROUND AND AIMS The transcription factor signal transducer and activator of transcription 3 (Stat3) has been considered to promote progression and metastasis of intestinal cancers. METHODS We investigated the role of Stat3 in intestinal tumors using mice with conditional ablation of Stat3 in intestinal epithelial cells (Stat3(DeltaIEC)). RESULTS In the Apc(Min) mouse model of intestinal cancer, genetic ablation of Stat3 reduced the multiplicity of early adenomas. However, loss of Stat3 promoted tumor progression at later stages, leading to formation of invasive carcinomas, which significantly shortened the lifespan of Stat3(DeltaIEC)Apc(Min/+) mice. Interestingly, loss of Stat3 in tumors of Apc(Min/+) mice had no significant impact on cell survival and angiogenesis, but promoted cell proliferation. A genome-wide expression analysis of Stat3-deficient tumors suggested that Stat3 might negatively regulate intestinal cancer progression via the cell adhesion molecule CEACAM1. CONCLUSIONS Our data suggest that Stat3 impairs invasiveness of intestinal tumors. Therefore, therapeutic targeting of the Stat3 signaling pathway in intestinal cancer should be evaluated for adverse effects on tumor progression.

The novel gaseous vasorelaxant hydrogen sulfide inhibits angiotensin-converting enzyme activity of endothelial cells

Objective Beside NO (nitric monoxide) and CO (carbon monoxide), H2S (hydrogen sulfide) has been identified recently as the third gasotransmitter. By acting directly on KATP-channels on smooth muscle cells (SMC) H2S possesses vasorelaxing properties. It has the potential to react with metal ions (i.e. Cu, Fe, Zn) in metalloproteins. Angiotensin-converting enzyme (ACE), responsible for vasoconstriction, is a zinc (Zn2+) containing enzyme. We therefore hypothesized that H2S may interact with the Zn2+ in the active center of ACE, modulating (inhibiting) enzyme activity. Methods ACE activity was measured on the surface of human endothelial cells (HUVECs) monolayers in culture, ex-vivo in umbilical veins and in HUVEC protein extracts. Quantitative real-time polymerase chain reaction (PCR) was used to study the effect of H2S on ACE mRNA expression in HUVECs. Results H2S inhibited the activity of ACE in HUVEC protein extracts in a dose-dependent manner, and only Zn2+ but not Cd2+, Ca2+ or Mg2+ could counteract the inhibitory effect. Cell-surface ACE activity was inhibited by H2S on HUVEC monolayers and in ex-vivo umbilical veins. No influence of H2S on ACE mRNA expression was observed. Conclusion H2S exhibits direct inhibitory action on ACE activity in HUVECs, obviously by interfering with the Zn2+ in the active center of the enzyme. Thus, beside the known influence of H2S on SMC KATP-channels, the observed direct ACE inhibitory effect may add to the vasorelaxant effect of H2S in the vasculature by reducing angiotensin II production and inhibiting bradykinin degradation.

Peroxisome Proliferator-activated Receptor (PPAR) γ Coactivator-1 Recruitment Regulates PPAR Subtype Specificity

The peroxisome proliferator-activated receptors (PPAR) α and γ play key roles in the transcriptional control of contrasting metabolic pathways such as adipogenesis and fatty acid β-oxidation. Both ligand-activated nuclear receptors bind to common target gene response elements and interact with distinct domains of the transcriptional coactivator PGC-1 to attain their full transcriptional potency. Thus, PPAR subtype specificity may be determined by ligand availability and transcription factor or coactivator expression levels. To identify other, perhaps more precise mechanisms contributing to PPAR subtype specificity, we studied PGC-1 recruitment by PPARs using a previously described hormone response element in the humanUCP1 promoter and a human brown adipocyte cell line as our model system. As in rodents, PGC-1 is involved in the transcriptional regulation of the UCP1 gene in humans and mediates the effects of PPARα and PPARγ agonists and retinoic acid. Interestingly, a previously postulated PGC-1 repressor selectively affects the PPARα-mediated activation of UCP1 gene expression. Furthermore, inhibition of p38 MAPK signaling, known to regulate the PGC-1/repressor interaction, decreases the stimulatory effect of PPARα agonist treatment without reducing the response to thiazolidinedione or retinoic acid. These data support a model whereby PPAR subtype specificity is regulated by recruitment of PGC-1.

Identification of mTOR as a novel bifunctional target in chronic myeloid leukemia: dissection of growth-inhibitory and VEGF-suppressive effects of rapamycin in leukemic cells

The mammalian target of rapamycin (mTOR) has recently been described to be constitutively activated in Bcr‐Abl‐transformed cells and to mediate rapamycin‐induced inhibition of growth in respective cell lines. We have recently shown that rapamycin down‐regulates expression of vascular endothelial growth factor (VEGF), a mediator of leukemia‐associated angiogenesis, in primary CML cells. In the present study, we analyzed growth‐inhibitory in vitro and in vivo effects of rapamycin on primary CML cells and asked whether rapamycin‐induced suppression of VEGF in leukemic cells is related to growth inhibition. Rapamycin dose dependently inhibited growth of primary CML cells obtained from patients with imatinib‐responsive or imatinib‐resistant disease as well as growth of Bcr‐Abl‐transformed imatinib‐resistant cell lines. Moreover, we observed potent cytoreductive effects of rapamycin in a patient with imatinib‐resistant Bcr‐Abl+ leukemia. The growth‐inhibitory effects of rapamycin on CML cells were found to be associated with G1 cell cycle arrest and with induction of apoptosis. In all cell types tested, rapamycin was found to down‐regulate expression of VEGF. However, exogenously added VEGF did not counteract the rapamycin‐induced decrease in proliferation. In conclusion, rapamycin inhibits growth of CML cells in vitro and in vivo and, in addition, down‐regulates expression of VEGF. Both effects may contribute to the antileukemic activity of the drug in CML.