PPARβ interprets a chromatin signature of pluripotency to promote embryonic differentiation at gastrulation

Peroxisome Proliferator-Activated Receptor α Agonist and Its Target Nanog Cooperate to Induce Pluripotency

The pharmaceutical compounds that modulate pluripotent stem cell (PSC) identity and function are increasingly adopted to generate qualified PSCs and their derivatives, which have promising potential in regenerative medicine, in pursuit of more accuracy and safety and less cost. Here, we demonstrate the peroxisome proliferator-activated receptor α (PPARα) agonist as a novel enhancer of pluripotency acquisition and induced pluripotent stem cell (iPSC) generation. We found that PPARα agonist, examined and selected Food and Drug Administration (FDA) -approved compound libraries, increase the expression of pluripotency-associated genes, such as Nanog, Nr5A2, Oct4, and Rex1, during the reprogramming process and facilitate iPSC generation by enhancing their reprogramming efficiency. A reprogramming-promoting effect of PPARα occurred via the upregulation of Nanog, which is essential for the induction and maintenance of pluripotency. Through bioinformatic analysis, we identified putative peroxisome proliferator responsive elements (PPREs) located within the promoter region of the Nanog gene. We also determined that PPARα can activate Nanog transcription by specific binding to putative PPREs. Taken together, our findings suggest that PPARα is an important regulator of PSC pluripotency and reprogramming, and PPARα agonists can be used to improve PSC technology and regenerative medicine.

Dynamics of nuclear receptor gene expression during Pacific oyster development

BACKGROUND

Nuclear receptors are a highly conserved set of ligand binding transcription factors, with essential roles regulating aspects of vertebrate and invertebrate biology alike. Current understanding of nuclear receptor regulated gene expression in invertebrates remains sparse, limiting our ability to elucidate gene function and the conservation of developmental processes across phyla. Here, we studied nuclear receptor expression in the early life stages of the Pacific oyster, Crassostrea gigas, to identify at which specific key stages nuclear receptors are expressed RESULTS: We used quantitative RT-PCR to determine the expression profiles of 34 nuclear receptors, revealing three developmental key stages, during which nuclear receptor expression is dynamically regulated: embryogenesis, mid development from gastrulation to trochophore larva, and late larval development prior to metamorphosis. Clustering of nuclear receptor expression patterns demonstrated that transcriptional regulation was not directly related to gene phylogeny, suggesting closely related genes may have distinct functions. Expression of gene homologs of vertebrate retinoid receptors suggests participation in organogenesis and shell-formation, as they are highly expressed at the gastrulation and trochophore larval initial shell formation stages. The ecdysone receptor homolog showed high expression just before larval settlement, suggesting a potential role in metamorphosis.

CONCLUSION

Throughout early oyster development nuclear receptors exhibited highly dynamic expression profiles, which were not confined by gene phylogeny. These results provide fundamental information on the presence of nuclear receptors during key developmental stages, which aids elucidation of their function in the developmental process. This understanding is essential as ligand sensing nuclear receptors can be disrupted by xenobiotics, a mode of action through which anthropogenic environmental pollutants have been found to mediate effects.

Inactivation of PPARβ/δ adversely affects satellite cells and reduces postnatal myogenesis

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a ubiquitously expressed gene with higher levels observed in skeletal muscle. Recently, our laboratory showed (Bonala S, Lokireddy S, Arigela H, Teng S, Wahli W, Sharma M, McFarlane C, Kambadur R. J Biol Chem 287: 12935-12951, 2012) that PPARβ/δ modulates myostatin activity to induce myogenesis in skeletal muscle. In the present study, we show that PPARβ/δ-null mice display reduced body weight, skeletal muscle weight, and myofiber atrophy during postnatal development. In addition, a significant reduction in satellite cell number was observed in PPARβ/δ-null mice, suggesting a role for PPARβ/δ in muscle regeneration. To investigate this, tibialis anterior muscles were injured with notexin, and muscle regeneration was monitored on days 3, 5, 7, and 28 postinjury. Immunohistochemical analysis revealed an increased inflammatory response and reduced myoblast proliferation in regenerating muscle from PPARβ/δ-null mice. Histological analysis confirmed that the regenerated muscle fibers of PPARβ/δ-null mice maintained an atrophy phenotype with reduced numbers of centrally placed nuclei. Even though satellite cell numbers were reduced before injury, satellite cell self-renewal was found to be unaffected in PPARβ/δ-null mice after regeneration. Previously, our laboratory had showed (Bonala S, Lokireddy S, Arigela H, Teng S, Wahli W, Sharma M, McFarlane C, Kambadur R. J Biol Chem 287: 12935-12951, 2012) that inactivation of PPARβ/δ increases myostatin signaling and inhibits myogenesis. Our results here indeed confirm that inactivation of myostatin signaling rescues the atrophy phenotype and improves muscle fiber cross-sectional area in both uninjured and regenerated tibialis anterior muscle from PPARβ/δ-null mice. Taken together, these data suggest that absence of PPARβ/δ leads to loss of satellite cells, impaired skeletal muscle regeneration, and postnatal myogenesis. Furthermore, our results also demonstrate that functional antagonism of myostatin has utility in rescuing these effects.

Epigenetic basis of opiate suppression of Bdnf gene expression in the ventral tegmental area

Brain-derived neurotrophic factor (BDNF) plays a crucial role in modulating neural and behavioral plasticity to drugs of abuse. Here, we demonstrate a persistent down-regulation of exon-specific Bdnf expression in the ventral tegmental area (VTA) in response to chronic opiate exposure, which is mediated by specific epigenetic modifications at the corresponding Bdnf gene promoters. Exposure to chronic morphine increases stalling of RNA polymerase II at these Bdnf promoters in VTA and alters permissive and repressive histone modifications and occupancy of their regulatory proteins at the specific promoters. Furthermore, we show that morphine suppresses binding of phospho-CREB (cAMP response element binding protein) to Bdnf promoters in VTA, which results from enrichment of trimethylated H3K27 at the promoters, and that decreased NURR1 (nuclear receptor related-1) expression also contributes to Bdnf repression and associated behavioral plasticity to morphine. These studies reveal novel epigenetic mechanisms of morphine-induced molecular and behavioral neuroadaptations.