👤 Michael Fritz

Stroke patients show some degree of spontaneous functional recovery, but this is not sufficient to prevent long-term disability. One promising approach is to characterize the dynamics of stroke recovery genes in the lesion and distant areas. We induced sensorimotor cortex lesions in adult C57BL/6J mice using photothrombosis and performed qPCR on selected brain areas at 14, 28, and 56 days post-stroke (P14-56). Based on the grid walk and rotating beam test, the mice were classified into two groups. The expression of cAMP pathway genes Show less

In the absence of ligands, the nuclear receptor PPARβ/δ recruits the NCOR and SMRT corepressors, which form complexes with HDAC3, to canonical target genes. Agonistic ligands cause dissociation of corepressors and enable enhanced transcription. Vice versa, synthetic inverse agonists augment corepressor recruitment and repression. Both basal repression of the target gene ANGPTL4 and reinforced repression elicited by inverse agonists are partially insensitive to HDAC inhibition. This raises the question how PPARβ/δ represses transcription mechanistically. We show that the PPARβ/δ inverse agonist PT-S264 impairs transcription initiation by decreasing recruitment of activating Mediator subunits, RNA polymerase II, and TFIIB, but not of TFIIA, to the ANGPTL4 promoter. Mass spectrometry identifies NCOR as the main PT-S264-dependent interactor of PPARβ/δ. Reconstitution of knockout cells with PPARβ/δ mutants deficient in basal repression results in diminished recruitment of NCOR, SMRT, and HDAC3 to PPAR target genes, while occupancy by RNA polymerase II is increased. PT-S264 restores binding of NCOR, SMRT, and HDAC3 to the mutants, resulting in reduced polymerase II occupancy. Our findings corroborate deacetylase-dependent and -independent repressive functions of HDAC3-containing complexes, which act in parallel to downregulate transcription. Show less

It is critical for survival to assign positive or negative valence to salient stimuli in a correct manner. Accordingly, harmful stimuli and internal states characterized by perturbed homeostasis are accompanied by discomfort, unease, and aversion. Aversive signaling causes extensive suffering during chronic diseases, including inflammatory conditions, cancer, and depression. Here, we investigated the role of melanocortin 4 receptors (MC4Rs) in aversive processing using genetically modified mice and a behavioral test in which mice avoid an environment that they have learned to associate with aversive stimuli. In normal mice, robust aversions were induced by systemic inflammation, nausea, pain, and κ opioid receptor-induced dysphoria. In sharp contrast, mice lacking MC4Rs displayed preference or indifference toward the aversive stimuli. The unusual flip from aversion to reward in mice lacking MC4Rs was dopamine dependent and associated with a change from decreased to increased activity of the dopamine system. The responses to aversive stimuli were normalized when MC4Rs were reexpressed on dopamine D1 receptor-expressing cells or in the striatum of mice otherwise lacking MC4Rs. Furthermore, activation of arcuate nucleus proopiomelanocortin neurons projecting to the ventral striatum increased the activity of striatal neurons in an MC4R-dependent manner and elicited aversion. Our findings demonstrate that melanocortin signaling through striatal MC4Rs is critical for assigning negative motivational valence to harmful stimuli. Show less

In human atherosclerotic lesions, degranulated mast cells are found in the vicinity of macrophage foam cells. Mast cell granules contain tryptase, a tetrameric serine protease requiring glycosaminoglycans for stabilization. No endogenous inhibitors have been described for tryptase, and the physiological functions of the enzyme are poorly understood. Here, we investigated the effects of human tryptase on the integrity of high density lipoprotein (HDL)3 and on its ability to release cholesterol from cultured mouse macrophage foam cells. Incubation of HDL3 with tryptase led to degradation of its apolipoproteins. Tryptase predominantly degraded a quantitatively minor subfraction of HDL3 that is lipid poor, exhibits electrophoretic pre-beta mobility, and contains either apolipoprotein A-I or apolipoprotein A-IV as its sole apolipoprotein. Moreover, tryptase caused functional changes in HDL3 by destroying its ability to promote high-affinity efflux of cholesterol from macrophage foam cells, ie, the pre-beta-HDL-dependent component of the process. Human aortic proteoglycans increased the ability of tryptase to proteolyze HDL3, suggesting that the proteoglycan-rich extracellular matrix of the arterial intima provides an appropriate environment for the extracellular actions of tryptase. By depleting pre-beta-HDL, mast cell tryptase may impair the initial step of reverse cholesterol transport and will then favor cellular accumulation of cholesterol during atherogenesis. Show less