Implication of satellite cell behaviors in capillary growth via VEGF expression-independent mechanism in response to mechanical loading in HeyL-null mice

Angiogenesis and muscle satellite cell (SC)-mediated myonuclear accretion are considered essential for the robust response of contraction-induced muscle hypertrophy. Moreover, both myonucleus and SCs are physically adjacent to capillaries and are the major sites for the expression of proangiogenic factors, such as VEGF, in the skeletal muscle. Thus, events involving the addition of new myonuclei via activation of SCs may play an important role in angiogenesis during muscle hypertrophy. However, the relevance among myonuclei number, capillary supply, and angiogenesis factor is not demonstrated. The Notch effector HeyL is specifically expressed in SCs in the skeletal muscle and is crucial for SC proliferation by inhibiting MyoD in overload-induced muscle hypertrophy. Here, we tested whether the addition of new myonuclei by SC in overloaded muscle is associated with angiogenic adaptation by reanalyzing skeletal muscle from HeyL-knockout (KO) mice, which show blunted responses of SC proliferation, myonucleus addition, and overload-induced muscle hypertrophy. Reanalysis confirmed blunted SC proliferation and myonuclear accretion in the plantaris muscle of HeyL-KO mice 9 wk after synergist ablation. Interestingly, the increase in capillary-to-fiber ratio observed in wild-type (WT) mice was impaired in HeyL-KO mice. In both WT and HeyL-KO mice, the expression of VEGFA and VEGFB was similarly increased in response to overload. In addition, the expression pattern of TSP-1, a negative regulator of angiogenesis, was also not changed between WT and HeyL-KO mice. Collectively, these results suggest that SCs activation-myonuclear accretion plays a crucial role in angiogenesis during overload-induced muscle hypertrophy via independent of angiogenesis regulators.

The Pathogenic Roles of IL-22 in Colitis: Its Transcription Regulation by Musculin in T Helper Subsets and Innate Lymphoid Cells

IL-22 plays a crucial role in promoting inflammation, antimicrobial immunity and tissue repair at barrier surfaces. The role of IL-22 in colitis is still controversial: while IL-22 has a protective effect on gut epithelium in acute injuries, it also enhances colitis in a context-dependent manner. Here, we summarize the Yin and Yang of IL-22 in colitis. Particularly, we emphasize the role of innate lymphoid cells (ILCs) in IL-22 production and regulation. A previously underappreciated transcription factor, Musculin (MSC), has been recently identified to be expressed in not only Th17 cells, but also RORγt+/Id2+ IL-22-producing group 3 ILCs in the gut of naïve mice. We hypothesize that the co-expression and interaction of MSC with the key transcription repressor Id2 in developing lymphoid cells (e.g., in LTi cells) and ILC precursors might fine tune the developmental programs or regulate the plasticity of adaptive Th subset and innate ILCs. The much-elevated expression of IL-22 in MSC-/- ILC3s suggests that MSC may function as: 1) a transcription suppressor for cytokines, particularly for IL-22, and/or 2) a gatekeeper for specific lineages of Th cells and innate ILCs as well. Amelioration of colitis symptoms in MSC-/- mice by IL-22-blocking agent IL-22BP-Fc suggests a counterintuitive pathogenic role of IL-22 in the absence of MSC as a checkpoint. The theory that exuberant production of IL-22 under pathological conditions (e.g., in human inflammatory bowel disease, IBD) may cause epithelial inflammation due to endoplasmic reticulum (ER) stress response is worth further investigation. Rheostatic regulation of IL-22 may be of therapeutic value to restore homeostatic balance and promote intestinal health in human colitis.

Maturation of Purkinje cell firing properties relies on neurogenesis of excitatory neurons

Preterm infants that suffer cerebellar insults often develop motor disorders and cognitive difficulty. Excitatory granule cells, the most numerous neuron type in the brain, are especially vulnerable and likely instigate disease by impairing the function of their targets, the Purkinje cells. Here, we use regional genetic manipulations and in vivo electrophysiology to test whether excitatory neurons establish the firing properties of Purkinje cells during postnatal mouse development. We generated mutant mice that lack the majority of excitatory cerebellar neurons and tracked the structural and functional consequences on Purkinje cells. We reveal that Purkinje cells fail to acquire their typical morphology and connectivity, and that the concomitant transformation of Purkinje cell firing activity does not occur either. We also show that our mutant pups have impaired motor behaviors and vocal skills. These data argue that excitatory cerebellar neurons define the maturation time-window for postnatal Purkinje cell functions and refine cerebellar-dependent behaviors.

The Aryl hydrocarbon receptor mediates reproductive toxicity of polychlorinated biphenyl congener 126 in rats

Polychlorinated biphenyls (PCBs) are endocrine disrupting chemicals with documented, though mechanistically ill-defined, reproductive toxicity. The toxicity of dioxin-like PCBs, such as PCB126, is mediated via the aryl hydrocarbon receptor (AHR) in non-ovarian tissues. The goal of this study was to examine the uterine and ovarian effects of PCB126 and test the hypothesis that the AHR is required for PCB126-induced reproductive toxicity. Female Holzman-Sprague Dawley wild type (n = 14; WT) and Ahr knock out (n = 11; AHR-/-) rats received a single intraperitoneal injection of either corn oil vehicle (5 ml/kg: WT_O and AHR-/-_O) or PCB126 (1.63 mg/kg in corn oil: WT_PCB and AHR-/-_PCB) at four weeks of age. The estrous cycle was synchronized and ovary and uterus were collected 28 days after exposure. In WT rats, PCB126 exposure reduced (P < 0.05) body and ovary weight, uterine gland number, uterine area, progesterone, 17β-estradiol and anti-Müllerian hormone level, secondary and antral follicle and corpora lutea number but follicle stimulating hormone level increased (P < 0.05). In AHR-/- rats, PCB126 exposure increased (P ≤ 0.05) circulating luteinizing hormone level. Ovarian or uterine mRNA abundance of biotransformation, and inflammation genes were altered (P < 0.05) in WT rats due to PCB126 exposure. In AHR-/- rats, the transcriptional effects of PCB126 were restricted to reductions (P < 0.05) in three inflammatory genes. These findings support a functional role for AHR in the female reproductive tract, illustrate AHR's requirement in PCB126-induced reprotoxicity, and highlight the potential risk of dioxin-like compounds on female reproduction.

HIF in the heart: development, metabolism, ischemia, and atherosclerosis

The heart forms early in development and delivers oxygenated blood to the rest of the embryo. After birth, the heart requires kilograms of ATP each day to support contractility for the circulation. Cardiac metabolism is omnivorous, utilizing multiple substrates and metabolic pathways to produce this energy. Cardiac development, metabolic tuning, and the response to ischemia are all regulated in part by the hypoxia-inducible factors (HIFs), central components of essential signaling pathways that respond to hypoxia. Here we review the actions of HIF1, HIF2, and HIF3 in the heart, from their roles in development and metabolism to their activity in regeneration and preconditioning strategies. We also discuss recent work on the role of HIFs in atherosclerosis, the precipitating cause of myocardial ischemia and the leading cause of death in the developed world.

PRC2 Regulated Atoh8 Is a Regulator of Intestinal Microfold Cell (M Cell) Differentiation

Intestinal microfold cells (M cells) are a dynamic lineage of epithelial cells that initiate mucosal immunity in the intestine. They are responsible for the uptake and transcytosis of microorganisms, pathogens, and other antigens in the gastrointestinal tract. A mature M cell expresses a receptor Gp2 which binds to pathogens and aids in the uptake. Due to the rarity of these cells in the intestine, their development and differentiation remain yet to be fully understood. We recently demonstrated that polycomb repressive complex 2 (PRC2) is an epigenetic regulator of M cell development, and 12 novel transcription factors including Atoh8 were revealed to be regulated by the PRC2. Here, we show that Atoh8 acts as a regulator of M cell differentiation; the absence of Atoh8 led to a significant increase in the number of Gp2+ mature M cells and other M cell-associated markers such as Spi-B and Sox8. In vitro organoid analysis of RankL treated organoid showed an increase of mature marker GP2 expression and other M cell-associated markers. Atoh8 null mice showed an increase in transcytosis capacity of luminal antigens. An increase in M cell population has been previously reported to be detrimental to mucosal immunity because some pathogens like orally acquired prions have been able to exploit the transcytosis capacity of M cells to infect the host; mice with an increased population of M cells are also susceptible to Salmonella infections. Our study here demonstrates that PRC2 regulated Atoh8 is one of the factors that regulate the population density of intestinal M cell in the Peyer's patch.

Transcription factor Ascl2 promotes germinal center B cell responses by directly regulating AID transcription

During germinal center (GC) reactions, activated B cells undergo clonal expansion and functional maturation to produce high-affinity antibodies and differentiate into plasma and memory cells, accompanied with class-switching recombination (CSR) and somatic hypermutation (SHM). Activation-induced cytidine deaminase (AID) is responsible for both CSR and SHM in GC B cells. Transcriptional mechanisms underlying AID regulation and GC B cell reactions are still not well understood. Here, we show that expression of Ascl2 transcription factor is upregulated in GC B cells. Ectopic expression of Ascl2 promotes GC B cell development and enhances antibody production and affinity maturation. Conversely, deletion of Ascl2 in B cells impairs the GC response. Genome-wide analysis reveals that Ascl2 directly regulates GC B cell-related genes, including AID; ectopic expression of AID in Ascl2-deficient B cells rescues their antibody defects. Thus, Ascl2 regulates AID transcription and promotes GC B cell responses.

Mosaic CRISPR-stop enables rapid phenotyping of nonsense mutations in essential genes

CRISPR-stop converts protein-coding sequences into stop codons, which, in the appropriate location, results in a null allele. CRISPR-stop induction in one-cell-stage zygotes generates Founder 0 (F0) mice that are homozygous mutants; this avoids mouse breeding and serves as a rapid screening approach for nonlethal genes. However, loss of function of 25% of mammalian genes causes early lethality. Here, we induced CRISPR-stop in one of the two blastomeres of the zygote, a method we name mosaic CRISPR-stop, to produce mosaic Atoh1 and Sox10 F0 mice; these mice not only survived longer than regular Atoh1/Sox10 knockout mice but also displayed their recognized cochlear phenotypes. Moreover, by using mosaic CRISPR-stop, we uncovered a previously unknown role of another lethal gene, Rbm24, in the survival of cochlear outer hair cells (OHCs), and we further validated the importance of Rbm24 in OHCs by using our Rbm24 conditional knockout model. Together, our results demonstrated that mosaic CRISPR-stop is reliable and rapid, and we believe this method will facilitate rapid genetic screening of developmentally lethal genes in the mouse inner ear and also in other organs.

Regulation of branched-chain amino acid metabolism by hypoxia-inducible factor in glioblastoma

Hypoxia-inducible factors (HIFs) mediate metabolic reprogramming in response to hypoxia. However, the role of HIFs in branched-chain amino acid (BCAA) metabolism remains unknown. Here we show that hypoxia upregulates mRNA and protein levels of the BCAA transporter LAT1 and the BCAA metabolic enzyme BCAT1, but not their paralogs LAT2-4 and BCAT2, in human glioblastoma (GBM) cell lines as well as primary GBM cells. Hypoxia-induced LAT1 protein upregulation is mediated by both HIF-1 and HIF-2 in GBM cells. Although both HIF-1α and HIF-2α directly bind to the hypoxia response element at the first intron of the human BCAT1 gene, HIF-1α is exclusively responsible for hypoxia-induced BCAT1 expression in GBM cells. Knockout of HIF-1α and HIF-2α significantly reduces glutamate labeling from BCAAs in GBM cells under hypoxia, which provides functional evidence for HIF-mediated reprogramming of BCAA metabolism. Genetic or pharmacological inhibition of BCAT1 inhibits GBM cell growth under hypoxia. Together, these findings uncover a previously unrecognized HIF-dependent metabolic pathway that increases GBM cell growth under conditions of hypoxic stress.

Decreased lymphatic HIF-2α accentuates lymphatic remodeling in lymphedema

Pathologic lymphatic remodeling in lymphedema evolves during periods of tissue inflammation and hypoxia through poorly defined processes. In human and mouse lymphedema, there is a significant increase of hypoxia inducible factor 1 α (HIF-1α), but a reduction of HIF-2α protein expression in lymphatic endothelial cells (LECs). We questioned whether dysregulated expression of these transcription factors contributes to disease pathogenesis and found that LEC-specific deletion of Hif2α exacerbated lymphedema pathology. Even without lymphatic vascular injury, the loss of LEC-specific Hif2α caused anatomic pathology and a functional decline in fetal and adult mice. These findings suggest that HIF-2α is an important mediator of lymphatic health. HIF-2α promoted protective phosphorylated TIE2 (p-TIE2) signaling in LECs, a process also replicated by upregulating TIE2 signaling through adenovirus-mediated angiopoietin-1 (Angpt1) gene therapy. Our study suggests that HIF-2α normally promotes healthy lymphatic homeostasis and raises the exciting possibility that restoring HIF-2α pathways in lymphedema could mitigate long-term pathology and disability.

The transcription factor E2A drives neural differentiation in pluripotent cells

The intrinsic mechanisms that link extracellular signalling to the onset of neural differentiation are not well understood. In pluripotent mouse cells, BMP blocks entry into the neural lineage via transcriptional upregulation of inhibitor of differentiation (Id) factors. We have previously identified the major binding partner of Id proteins in pluripotent cells as the basic helix-loop-helix (bHLH) transcription factor (TF) E2A. Id1 can prevent E2A from forming heterodimers with bHLH TFs or from forming homodimers. Here, we show that overexpression of a forced E2A homodimer is sufficient to drive robust neural commitment in pluripotent cells, even under non-permissive conditions. Conversely, we find that E2A null cells display a defect in their neural differentiation capacity. E2A acts as an upstream activator of neural lineage genes, including Sox1 and Foxd4, and as a repressor of Nodal signalling. Our results suggest a crucial role for E2A in establishing neural lineage commitment in pluripotent cells.

Dec1 Deficiency Suppresses Cardiac Perivascular Fibrosis Induced by Transverse Aortic Constriction

Cardiac fibrosis is a major cause of cardiac dysfunction in hypertrophic hearts. Differentiated embryonic chondrocyte gene 1 (Dec1), a basic helix–loop–helix transcription factor, has circadian expression in the heart; however, its role in cardiac diseases remains unknown. Therefore, using Dec1 knock-out (Dec1KO) and wild-type (WT) mice, we evaluated cardiac function and morphology at one and four weeks after transverse aortic constriction (TAC) or sham surgery. We found that Dec1KO mice retained cardiac function until four weeks after TAC. Dec1KO mice also revealed more severely hypertrophic hearts than WT mice at four weeks after TAC, whereas no significant change was observed at one week. An increase in Dec1 expression was found in myocardial and stromal cells of TAC-treated WT mice. In addition, Dec1 circadian expression was disrupted in the heart of TAC-treated WT mice. Cardiac perivascular fibrosis was suppressed in TAC-treated Dec1KO mice, with positive immunostaining of S100 calcium binding protein A4 (S100A4), alpha smooth muscle actin (αSMA), transforming growth factor beta 1 (TGFβ1), phosphorylation of Smad family member 3 (pSmad3), tumor necrosis factor alpha (TNFα), and cyclin-interacting protein 1 (p21). Furthermore, Dec1 expression was increased in myocardial hypertrophy and myocardial infarction of autopsy cases. Taken together, our results indicate that Dec1 deficiency suppresses cardiac fibrosis, preserving cardiac function in hypertrophic hearts. We suggest that Dec1 could be a new therapeutic target in cardiac fibrosis.

Atoh8 acts as a regulator of chondrocyte proliferation and differentiation in endochondral bones

Atonal homolog 8 (Atoh8) is a transcription factor of the basic helix-loop-helix (bHLH) protein family, which is expressed in the cartilaginous elements of endochondral bones. To analyze its function during chondrogenesis we deleted Atoh8 in mice using a chondrocyte- (Atoh8flox/flox;Col2a1-Cre) and a germline- (Atoh8flox/flox;Prx1-Crefemale) specific Cre allele. In both strains, Atoh8 deletion leads to a reduced skeletal size of the axial and appendicular bones, but the stages of phenotypic manifestations differ. While we observed obviously shortened bones in Atoh8flox/flox;Col2a1-Cre mice only postnatally, the bones of Atoh8flox/flox;Prx1-Crefemale mice are characterized by a reduced bone length already at prenatal stages. Detailed histological and molecular investigations revealed reduced zones of proliferating and hypertrophic chondrocytes. In addition, Atoh8 deletion identified Atoh8 as a positive regulator of chondrocyte proliferation. As increased Atoh8 expression is found in the region of prehypertrophic chondrocytes where the expression of Ihh, a main regulator of chondrocyte proliferation and differentiation, is induced, we investigated a potential interaction of Atoh8 function and Ihh signaling. By activating Ihh signaling with Purmorphamine we demonstrate that Atoh8 regulates chondrocyte proliferation in parallel or downstream of Ihh signaling while it acts on the onset of hypertrophy upstream of Ihh likely by modulating Ihh expression levels.

Effects of Aryl Hydrocarbon Receptor Deficiency on PCB-77-Induced Impairment of Glucose Homeostasis during Weight Loss in Male and Female Obese Mice

BACKGROUND

Lipophilic polychlorinated biphenyls (PCBs) accumulate with obesity, but during weight loss, liberated PCBs act as ligands of the aryl hydrocarbon receptor (AhR) to negatively influence health. Previous studies demonstrated that PCB-77 administration to obese male mice impaired glucose tolerance during weight loss. Recent studies indicate higher toxic equivalencies of dioxin-like PCBs in exposed females than males.

OBJECTIVES

We compared effects of PCB-77 on weight gain or loss and glucose homeostasis in male vs. female mice. We defined effects of AhR deficiency during weight gain or loss in male and female mice exposed to PCB-77.

METHODS

Study design was vehicle (VEH) or PCB-77 administration while fed a high-fat (HF) diet for 12 wk, followed by weight loss for 4 wk. The following groups were examined: male and female C57BL/6 mice administered VEH or PCB-77, female [Formula: see text] and [Formula: see text] mice administered VEH or PCB-77, and male [Formula: see text] and [Formula: see text] mice administered PCB-77. Glucose tolerance was quantified during weight gain (week 11) and loss (week 15); liver and adipose AhR and IRS2 (insulin receptor substrate 2) mRNA abundance, and PCB-77 concentrations were quantified at week 16.

RESULTS

PCB-77 attenuated development of obesity in females but not males. During weight loss, PCB-77 impaired glucose tolerance of males. AhR-deficient females (VEH) were resistant to diet-induced obesity. Compared with VEH-treated mice, HF-fed [Formula: see text] females treated with PCB-77 has less weight gain, and [Formula: see text] females had greater weight gain. During weight loss, [Formula: see text] females but not [Formula: see text] males treated with PCB-77 exhibited impaired glucose tolerance. In [Formula: see text] females administered PCB-77, IRS2 mRNA abundance was lower in adipose tissue compared with VEH-treated mice.

CONCLUSION

Male and female mice responded differently to PCB-77 and AhR deficiency in body weight (BW) regulation and glucose homeostasis. AhR deficiency reversed PCB-77-induced glucose impairment of obese males losing weight but augmented glucose intolerance of females. These results demonstrate sex differences in PCB-77-induced regulation of glucose homeostasis of mice. https://doi.org/10.1289/EHP4133.

Zebrin II Is Ectopically Expressed in Microglia in the Cerebellum of Neurogenin 2 Null Mice

Zebrin II/aldolase C expression in the normal cerebellum is restricted to a Purkinje cell subset and is the canonical marker for stripes and zones. This spatial restriction has been confirmed in over 30 species of mammals, birds, fish, etc. In a transgenic mouse model in which the Neurogenin 2 gene has been disrupted (Neurog2^-/-), the cerebellum is smaller than normal and Purkinje cell dendrites are disordered, but the basic zone and stripe architecture is preserved. Here, we show that in the Neurog2^-/- mouse, in addition to the normal Purkinje cell expression, zebrin II is also expressed in a population of cells with a morphology characteristic of microglia. This identity was confirmed by double immunohistochemistry for zebrin II and the microglial marker, Iba1. The expression of zebrin II in cerebellar microglia is not restricted by zone or stripe or lamina. A second zone and stripe marker, PLCβ4, does not show the same ectopic expression. When microglia are compared in control vs. Neurog2^-/- mice, no difference is seen in apparent number or distribution, suggesting that the ectopic zebrin II immunoreactivity in Neurog2^-/- cerebellum reflects an ectopic expression rather than the invasion of a new population of microglia from the periphery. This ectopic expression of zebrin II in microglia is unique as it is not seen in numerous other models of cerebellar disruption, such as in Acp2^-/- mice and in human pontocerebellar hypoplasia. The upregulation of zebrin II in microglia is thus specific to the disruption of Neurog2 downstream pathways, rather than a generic response to a cerebellar disruption.

The Tcf21 lineage constitutes the lung lipofibroblast population

Transcription factor 21 (Tcf21) is a basic helix-loop-helix transcription factor required for mesenchymal development in several organs. Others have demonstrated that Tcf21 is expressed in embryonic lung mesenchyme and that loss of Tcf21 results in a pulmonary hypoplasia phenotype. Although recent single-cell transcriptome analysis has described multiple mesenchymal cell types in the lung, few have characterized the Tcf21 expressing population. To explore the Tcf21 mesenchymal lineage, we traced Tcf21-expressing cells during embryogenesis and in the adult. Our results showed that Tcf21 progenitor cells at embryonic day (E)11.5 generated a subpopulation of fibroblasts and lipofibroblasts and a limited number of smooth muscle cells. After E15.5, Tcf21 progenitor cells exclusively become lipofibroblasts and interstitial fibroblasts. Lipid metabolism genes were highly expressed in perinatal and adult Tcf21 lineage cells. Overexpression of Tcf21 in primary neonatal lung fibroblasts led to increases in intracellular neutral lipids, suggesting a regulatory role for Tcf21 in lipofibroblast function. Collectively, our results reveal that Tcf21 expression after E15.5 delineates the lipofibroblast and a population of interstitial fibroblasts. The Tcf21 inducible Cre mouse line provides a novel method for identifying and manipulating the lipofibroblast.

TGFβ1 signaling sustains aryl hydrocarbon receptor (AHR) expression and restrains the pathogenic potential of TH17 cells by an AHR-independent mechanism

The aryl hydrocarbon receptor (AHR) is a transcription factor activated by ligand highly expressed on TH17 cells, and AHR-deficient CD4+ T cells have impaired production of IL-17A and IL-22. Although AHR activation can exacerbate in vivo TH17 cell-mediated autoimmunity, accumulating data indicate that AHR is a nonpathogenic TH17 marker. Thus it remains unclear how AHR activation is regulated and impacts on the generation of TH17 subsets. Here we demonstrated that AHR pathway is activated during in vitro pathogenic TH17 polarization, but it is quickly downregulated. Under these conditions, additional AHR activation promoted IL-22 but not IL-17A. Interestingly, AHR high sustained expression and IL-17A promotion were only achieved when TGFβ1 was present in the culture. In addition to the effect on AHR regulation, TGFβ1 presented a dual role by simultaneously suppressing the TH17 pathogenic phenotype acquisition. This latter effect was independent of AHR stimulation, since its activation did not confer a TH17 anti-inflammatory profile and Ahr-/- cells did not upregulate any TH17 pathogenic marker. Through the use of EAE model, we demonstrated that AHR is still functional in encephalitogenic CD4+ T cells and the adoptive transfer of Ahr-/- TH17 cells to recipient mice resulted in milder EAE development when compared to their WT counterparts. Altogether, our data demonstrated that although AHR is highly expressed on in vitro-generated nonpathogenic TH17 cells, its ligation does not shift TH17 cells to an anti-inflammatory phenotype. Further studies investigating the role of AHR beyond TH17 differentiation may provide a useful understanding of the physiopathology of autoimmune diseases.

Conditional deletion of Ahr alters gene expression profiles in hematopoietic stem cells

The aryl hydrocarbon receptor (AHR) is a ligand activated bHLH transcription factor that belongs to the Per-Arnt-Sim (PAS) superfamily of proteins involved in mediating responses to cellular environment regulating normal physiological and developmental pathways. The AHR binds a broad range of naturally derived and synthetic compounds, and plays a major role in mediating effects of certain environmental chemicals. Although our understanding of the physiological roles of the AHR in the immune system is evolving, there is little known about its role in hematopoiesis and hematopoietic diseases. Prior studies demonstrated that AHR null (AHR-KO) mice have impaired hematopoietic stem cell (HSC) function; they develop myeloproliferative changes in peripheral blood cells, and alterations in hematopoietic stem and progenitor cell populations in the bone marrow. We hypothesized mice lacking AHR expression only within hematopoietic cells (AHRVav1 mice) would develop similar changes. However, we did not observe a complete phenocopy of AHR-KO and AHRVav1 animals at 2 or 18 months of age. To illuminate the signaling mechanisms underlying the alterations in hematopoiesis observed in these mice, we sorted a population of cells highly enriched for HSC function (LSK cells: CD34-CD48-CD150+) and performed microarray analyses. Ingenuity Pathway and Gene Set Enrichment Analyses revealed that that loss of AHR within HSCs alters several gene and signaling networks important for HSC function. Differences in gene expression networks among HSCs from AHR-KO and AHRVav1 mice suggest that AHR in bone marrow stromal cells also contributes to HSC function. In addition, numerous studies have suggested a role for AHR in both regulation of hematopoietic cells, and in the development of blood diseases. More work is needed to define what these signals are, and how they act upon HSCs.

Loss of Atoh1 from neurons regulating hypoxic and hypercapnic chemoresponses causes neonatal respiratory failure in mice

Atoh1-null mice die at birth from respiratory failure, but the precise cause has remained elusive. Loss of Atoh1 from various components of the respiratory circuitry (e.g. the retrotrapezoid nucleus (RTN)) has so far produced at most 50% neonatal lethality. To identify other Atoh1-lineage neurons that contribute to postnatal survival, we examined parabrachial complex neurons derived from the rostral rhombic lip (rRL) and found that they are activated during respiratory chemochallenges. Atoh1-deletion from the rRL does not affect survival, but causes apneas and respiratory depression during hypoxia, likely due to loss of projections to the preBötzinger Complex and RTN. Atoh1 thus promotes the development of the neural circuits governing hypoxic (rRL) and hypercapnic (RTN) chemoresponses, and combined loss of Atoh1 from these regions causes fully penetrant neonatal lethality. This work underscores the importance of modulating respiratory rhythms in response to chemosensory information during early postnatal life.

Pulmonary neuroendocrine cells amplify allergic asthma responses

Pulmonary neuroendocrine cells (PNECs) are rare airway epithelial cells whose function is poorly understood. Here we show that Ascl1-mutant mice that have no PNECs exhibit severely blunted mucosal type 2 response in models of allergic asthma. PNECs reside in close proximity to group 2 innate lymphoid cells (ILC2s) near airway branch points. PNECs act through calcitonin gene-related peptide (CGRP) to stimulate ILC2s and elicit downstream immune responses. In addition, PNECs act through the neurotransmitter γ-aminobutyric acid (GABA) to induce goblet cell hyperplasia. The instillation of a mixture of CGRP and GABA in Ascl1-mutant airways restores both immune and goblet cell responses. In accordance, lungs from human asthmatics show increased PNECs. These findings demonstrate that the PNEC-ILC2 neuroimmunological modules function at airway branch points to amplify allergic asthma responses.

The Retinal Circadian Clock and Photoreceptor Viability

Circadian rhythms are present in most living organisms, and these rhythms are not just a consequence of the day/night fluctuation, but rather they are generated by endogenous biological clocks with a periodicity of about 24 h. In mammals, the master pacemaker of circadian rhythms is localized in the suprachiasmatic nuclei (SCN) of the hypothalamus. The SCN controls circadian rhythms in peripheral organs. The retina also contains circadian clocks which regulate many aspects of retinal physiology, independently of the SCN. Emerging experimental evidence indicates that the retinal circadian clocks also affect ocular health, and a few studies have now demonstrated that disruption of retinal clocks may contribute to the development of retinal diseases. Our study indicates that in mice lacking the clock gene Bmal1, photoreceptor viability during aging is significantly reduced. Bmal1 knockout mice at 8-9 months of age have 20-30% less nuclei in the outer nuclear layer. No differences were observed in the other retinal layers. Our study suggests that the retinal circadian clock is an important modulator of photoreceptor health.

Editor's Highlight: Ah Receptor Activation Potentiates Neutrophil Chemoattractant (C-X-C Motif) Ligand 5 Expression in Keratinocytes and Skin

Chemokines are components of the skin microenvironment, which enable immune cell chemotaxis. Traditionally, transcription factors involved in inflammatory signaling (eg, NFκB) are important mediators of chemokine expression. To what extent xenobiotics and their associated receptors control chemokine expression is poorly understood. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor known to mediate physiological responses in the skin through the regulation of genes involved in xenobiotic metabolism, epidermal differentiation, and immunity. Here, we demonstrate that AHR activation within primary mouse keratinocytes regulates the expression of a neutrophil directing chemokine (C-X-C motif) ligand 5 (Cxcl5). AHR-mediated regulation of Cxcl5 is because of direct transcriptional activity upon treatment with AHR agonists such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Additionally, AHR mediates enhanced induction of Cxcl5 upon exposure to an agonist and the inflammatory cytokine interleukin 1 beta. This synergy is confined primarily to keratinocytes, as dermal fibroblasts did not achieve the same level of combinatorial induction. AHR-specific antagonists were able to reduce basal and induced levels of Cxcl5, demonstrating the potential for pharmacological intervention. Exposure of C57BL/6 J mice to ultraviolet (UV) light followed by topical treatment with the AHR agonist formylindolo(3,2-b)carbazole (FICZ) significantly induced Cxcl5 expression in skin compared with UV alone, and this response was absent in Ahr-/- mice. These results establish AHR as an important mediator of Cxcl5, with implications for the treatment of inflammatory skin diseases.

Hepatic hypoxia-inducible factors inhibit PPARα expression to exacerbate acetaminophen induced oxidative stress and hepatotoxicity

Oxidative stress has a critical role in the pathogenesis of acetaminophen (APAP) induced hepatocellular necrosis, and the identification of novel approaches to attenuate oxidative stress is essential to prevent/revert the disease. This study investigated the role of both HIF-1 and HIF-2 in the pathogenesis of APAP-induced oxidative stress, as well as the underlying mechanisms. In the present study, we initially found that knockout of HIF-1α or HIF-2α reduced APAP toxicity, and double knockout afforded the best protection. APAP treatment led to stabilization of both HIF-1α and HIF-2α in mouse livers. Moreover, the protective effects of HIF deficiency were related to the attenuated oxidative stress. Further experiments proved that PPARα, a master regulator in cellular metabolism accounted for the HIF deficiency-caused protective impact on APAP toxicity. Inactivation of HIFs promoted the expression of peroxisome proliferator-activated receptor α (PPARα) in the liver, which in turn activated nuclear factor erythroid 2-related factor 2 (Nrf2). Knockdown of PPARα or Nrf2 negated the hepatoprotection afforded by HIF deficiency. At last，examination of the PPARα promoter identified a HIF-binding site and HIF-dependent repression of PPARα in hepatocytes by luciferase reporter and EMSA study. Taken together， Our results demonstrate that HIFs are key suppressors of PPARα in the liver, thereby compromising the adaptive defense mechanisms against oxidative stress when confronted with APAP. These findings are important to the etiology and therapeutics of APAP hepatotoxicity. The functional link between HIFs and PPARα may have more implications in liver physiology and other pathologic conditions than APAP injury.

Spiral Ganglion Neuron Projection Development to the Hindbrain in Mice Lacking Peripheral and/or Central Target Differentiation

We investigate the importance of the degree of peripheral or central target differentiation for mouse auditory afferent navigation to the organ of Corti and auditory nuclei in three different mouse models: first, a mouse in which the differentiation of hair cells, but not central auditory nuclei neurons is compromised (Atoh1-cre; Atoh1f/f ); second, a mouse in which hair cell defects are combined with a delayed defect in central auditory nuclei neurons (Pax2-cre; Atoh1f/f ), and third, a mouse in which both hair cells and central auditory nuclei are absent (Atoh1-/-). Our results show that neither differentiated peripheral nor the central target cells of inner ear afferents are needed (hair cells, cochlear nucleus neurons) for segregation of vestibular and cochlear afferents within the hindbrain and some degree of base to apex segregation of cochlear afferents. These data suggest that inner ear spiral ganglion neuron processes may predominantly rely on temporally and spatially distinct molecular cues in the region of the targets rather than interaction with differentiated target cells for a crude topological organization. These developmental data imply that auditory neuron navigation properties may have evolved before auditory nuclei.

Hypogonadotropic Hypogonadism and Short Stature in Patients with Diabetes Due to Neurogenin 3 Deficiency

CONTEXT

Biallelic mutations in NEUROG3 are known to cause early-onset malabsorptive diarrhea due to congenital anendocrinosis and diabetes mellitus at a variable age. No other endocrine disorders have been described so far. We report four patients with homozygous NEUROG3 mutations who presented with short stature and failed to show any signs of pubertal development.

CASE DESCRIPTION

Four patients (two males, two females) were diagnosed with homozygous mutations in NEUROG3 on the basis of congenital malabsorptive diarrhea and diabetes. All four had severe short stature and failed to develop secondary sexual characteristics at an appropriate age, despite some having normal body mass index. The absence of gonadal function persisted into the third decade in one patient. Upon testing, both basal and stimulated LH and FSH levels were low, with the remaining pituitary hormones within the normal range. Magnetic resonance imaging scans of the hypothalamic-pituitary axis did not reveal structural abnormalities. A diagnosis of hypogonadotropic hypogonadism was made, and replacement therapy with sex hormones was started.

CONCLUSIONS

The high reproducibility of this novel phenotype suggests that central hypogonadism and short stature are common findings in patients with mutations in NEUROG3. Growth rate needs to be carefully monitored in these patients, who also should be routinely screened for hypogonadism when they reach the appropriate age. NEUROG3 mutations expand on the growing number of genetic causes of acquired hypogonadotropic hypogonadism.

The hyaloid vasculature facilitates basement membrane breakdown during choroid fissure closure in the zebrafish eye

A critical aspect of vertebrate eye development is closure of the choroid fissure (CF). Defects in CF closure result in colobomas, which are a significant cause of childhood blindness worldwide. Despite the growing number of mutated loci associated with colobomas, we have a limited understanding of the cell biological underpinnings of CF closure. Here, we utilize the zebrafish embryo to identify key phases of CF closure and regulators of the process. Utilizing Laminin-111 as a marker for the basement membrane (BM) lining the CF, we determine the spatial and temporal patterns of BM breakdown in the CF, a prerequisite for CF closure. Similarly, utilizing a combination of in vivo time-lapse imaging, β-catenin immunohistochemistry and F-actin staining, we determine that tissue fusion, which serves to close the fissure, follows BM breakdown closely. Periocular mesenchyme (POM)-derived endothelial cells, which migrate through the CF to give rise to the hyaloid vasculature, possess distinct actin foci that correlate with regions of BM breakdown. Disruption of talin1, which encodes a regulator of the actin cytoskeleton, results in colobomas and these correlate with structural defects in the hyaloid vasculature and defects in BM breakdown. cloche mutants, which entirely lack a hyaloid vasculature, also possess defects in BM breakdown in the CF. Taken together, these data support a model in which the hyaloid vasculature and/or the POM-derived endothelial cells that give rise to the hyaloid vasculature contribute to BM breakdown during CF closure.

Resolving early mesoderm diversification through single-cell expression profiling

In mammals, specification of the three major germ layers occurs during gastrulation, when cells ingressing through the primitive streak differentiate into the precursor cells of major organ systems. However, the molecular mechanisms underlying this process remain unclear, as numbers of gastrulating cells are very limited. In the mouse embryo at embryonic day 6.5, cells located at the junction between the extra-embryonic region and the epiblast on the posterior side of the embryo undergo an epithelial-to-mesenchymal transition and ingress through the primitive streak. Subsequently, cells migrate, either surrounding the prospective ectoderm contributing to the embryo proper, or into the extra-embryonic region to form the yolk sac, umbilical cord and placenta. Fate mapping has shown that mature tissues such as blood and heart originate from specific regions of the pre-gastrula epiblast, but the plasticity of cells within the embryo and the function of key cell-type-specific transcription factors remain unclear. Here we analyse 1,205 cells from the epiblast and nascent Flk1(+) mesoderm of gastrulating mouse embryos using single-cell RNA sequencing, representing the first transcriptome-wide in vivo view of early mesoderm formation during mammalian gastrulation. Additionally, using knockout mice, we study the function of Tal1, a key haematopoietic transcription factor, and demonstrate, contrary to previous studies performed using retrospective assays, that Tal1 knockout does not immediately bias precursor cells towards a cardiac fate.

Loss of Hif-2α Rescues the Hif-1α Deletion Phenotype of Neonatal Respiratory Distress In Mice

Hypoxia is a state of decreased oxygen reaching the tissues of the body. During prenatal development, the fetus experiences localized occurrences of hypoxia that are essential for proper organogenesis and survival. The response to decreased oxygen availability is primarily regulated by hypoxia-inducible factors (HIFs), a family of transcription factors that modulate the expression of key genes involved in glycolysis, angiogenesis, and erythropoiesis. HIF-1α and HIF-2α, two key isoforms, are important in embryonic development, and likely are involved in lung morphogenesis. We have recently shown that the inducible loss of Hif-1α in lung epithelium starting at E4.5 leads to death within an hour of parturition, with symptoms similar to neonatal respiratory distress syndrome (RDS). In addition to Hif-1α, Hif-2α is also expressed in the developing lung, although the overlapping roles of Hif-1α and Hif-2α in this context are not fully understood. To further investigate the independent role of Hif-2α in lung epithelium and its ability to alter Hif-1α-mediated lung maturation, we generated two additional lung-specific inducible Hif-α knockout models (Hif-2α and Hif-1α+Hif-2α). The intrauterine loss of Hif-2α in the lungs does not lead to decreased viability or observable phenotypic changes in the lung. More interestingly, survivability observed after the loss of both Hif-1α and Hif-2α suggests that the loss of Hif-2α is capable of rescuing the neonatal RDS phenotype seen in Hif-1α-deficient pups. Microarray analyses of lung tissue from these three genotypes identified several factors, such as Scd1, Retlnγ, and Il-1r2, which are differentially regulated by the two HIF-α isoforms. Moreover, network analysis suggests that modulation of hormone-mediated, NF-κB, C/EBPα, and c-MYC signaling are central to HIF-mediated changes in lung development.

Porcupine inhibitor suppresses paracrine Wnt-driven growth of Rnf43;Znrf3-mutant neoplasia

Rnf43 (RING finger protein 43) and Znrf3 (zinc/RING finger protein 3) (RZ) are two closely related transmembrane E3 ligases, encoded by Wnt target genes, that remove surface Wnt (wingless-int) receptors. The two genes are mutated in various human cancers. Such tumors are predicted to be hypersensitive to, yet still depend on, secreted Wnts. We previously showed that mutation of RZ in the intestine yields rapidly growing adenomas containing LGR5(+) (leucine-rich repeat-containing G-protein coupled receptor 5) stem cells and Wnt3-producing Paneth cells. We now show that removal of Paneth cells by Math1 mutation inhibits RZ(-/-) tumor formation. Similarly, deletion of Wnt3 inhibits tumorigenesis. Treatment of mice carrying RZ(-/-) intestinal neoplasia with a small molecule Wnt secretion inhibitor (porcupine inhibitor C59) strongly inhibited growth, whereas adjacent normal crypts remained intact. These results establish that paracrine Wnt secretion is an essential driver of RZ(-/-) tumor growth and imply that a therapeutic window exists for the use of porcupine inhibitors for RZ-mutant cancers.

Effects of postweaning administration of conjugated linoleic acid on development of obesity in nescient basic helix-loop-helix 2 knockout mice

Conjugated linoleic acid (CLA) has been reported to prevent body weight gain and fat accumulation in part by improving physical activity in mice. However, the effects of postweaning administration of CLA on the development of obesity later in life have not yet been demonstrated. The current study investigated the role of postweaning CLA treatment on skeletal muscle energy metabolism in genetically induced inactive adult-onset obese model, nescient basic helix-loop-helix 2 knockout (N2KO) mice. Four-week-old male N2KO and wild type mice were fed either control or a CLA-containing diet (0.5%) for 4 weeks, and then CLA was withdrawn and control diet provided to all mice for the following 8 weeks. Postweaning CLA supplementation in wild type animals, but not N2KO mice, may activate AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-δ (PPARδ) as well as promote desensitization of phosphatase and tensin homologue (PTEN) and sensitization of protein kinase B (AKT) at threonine 308 in gastrocnemius skeletal muscle, improving voluntary activity and glucose homeostasis. We suggest that postweaning administration of CLA may in part stimulate the underlying molecular targets involved in muscle energy metabolism to reduce weight gain in normal animals, but not in the genetically induced inactive adult-onset animal model.

[Nuclear protein 1 knockdown inhibits proliferation and migration of HepG2 cells]

OBJECTIVE

To observe the expression of nuclear protein 1 (Nupr1), a stress-related nuclear protein, in a panel of human hepatocellular carcinoma cell lines, and its effects on the proliferation and migration of hepatocellular carcinoma cells by RNA interference-mediated knockdown.

METHODS

Real-time quantitative PCR was employed to detect Nupr1 mRNA levels in hepatocellular carcinoma cell lines, including BEL-7402, QSG-7703, SMMC-7721 and HepG2. After Nupr1 expression was knocked down by RNA interference, cell proliferation was monitored by MTT assay and colony formation in plate. Cell cycle was analyzed by flow cytometry and cell migration was assayed by TranswellTM assay.

RESULTS

Higher expression of Nupr1 was detected in HepG2 as compared with the other cell lines. Nupr1 expression in HepG2 cells were efficiently knocked down by two short hairpin RNAs (shRNAs), with inhibitory rates being 72.25% and 84.25%, respectively. HepG2 cells with Nupr1 knockdown displayed lower rate of proliferation, G1 arrest, and significantly decreased abilities of cell migration and colony formation. Western blotting showed that Nupr1 knockdown increased the expressions of p21 and p27, two negative regulators of cell cycle.

CONCLUSION

Knockdown of Nupr1 inhibited the proliferation and migration of HepG2 hepatocellular carcinoma cells.

The Group 3 Innate Lymphoid Cell Defect in Aryl Hydrocarbon Receptor Deficient Mice Is Associated with T Cell Hyperactivation during Intestinal Infection

Intestinal infection with the intracellular parasite Toxoplasma gondii results in the translocation of commensal bacteria to peripheral organs and the development of a T cell response specific to the microbiota. In naïve mice, the recently described RORγt+ group 3 innate lymphoid cell (ILC) population plays a critical role in promoting intestinal barrier function and limiting responses to gut-resident commensal bacteria. Given this role for group 3 ILCs, studies were performed to evaluate whether these cells might influence the immune response to mucosal infection with T. gondii. Phenotypic characterization of RORγt+ ILCs in T. gondii infected mice revealed that this population decreased following challenge but the population that remained expressed costimulatory molecules and IL-22. One factor that influences the maintenance of RORγt+ ILCs is the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, and Ahr-/- mice have a marked defect in the lamina propria group 3 ILC population. When Ahr-/- mice were challenged with T. gondii, they lost more weight than wild type controls. This disease course in Ahr-/- animals was associated with increased T cell responses to Toxoplasma antigen and crude commensal antigen preparations. Together, these data suggest that group 3 ILCs have a role in limiting T cell activation during intestinal infection.

Effects of Npas4 deficiency on anxiety, depression-like, cognition and sociability behaviour

The transcription factor neuronal PAS domain-containing protein 4 (Npas4), which regulates the formation of inhibitory synapses on excitatory neurons, has been suggested as a candidate gene for neurological and psychiatric conditions such as bipolar depression, autism spectrum and cognitive disorders. A mouse model of Npas4 deficiency has been developed to investigate any role in these disorders. Behavioural characterisation of Npas4(-/-), Npas4(+/-) and Npas4(+/+) mice has been conducted using the open field, elevated zero maze (EZM), Y-maze, sociability test and forced swim test (FST) to investigate a range of behaviours. Npas4(-/-) mice spent more time in the open arm of the EZM than other genotypes, suggesting decreased anxiety-like behaviour. Npas4(+/-) mice, however, were more immobile in the FST than other genotypes, suggesting increased depression-like behaviour, and also showed impaired spatial recognition memory in the Y-maze. There were no differences between genotype in social behaviour. These results suggest that differential levels of Npas4 expression in the brain may regulate anxiety, depression and cognition related disorders.

Mice lacking the circadian modulators SHARP1 and SHARP2 display altered sleep and mixed state endophenotypes of psychiatric disorders

Increasing evidence suggests that clock genes may be implicated in a spectrum of psychiatric diseases, including sleep and mood related disorders as well as schizophrenia. The bHLH transcription factors SHARP1/DEC2/BHLHE41 and SHARP2/DEC1/BHLHE40 are modulators of the circadian system and SHARP1/DEC2/BHLHE40 has been shown to regulate homeostatic sleep drive in humans. In this study, we characterized Sharp1 and Sharp2 double mutant mice (S1/2-/-) using online EEG recordings in living animals, behavioral assays and global gene expression profiling. EEG recordings revealed attenuated sleep/wake amplitudes and alterations of theta oscillations. Increased sleep in the dark phase is paralleled by reduced voluntary activity and cortical gene expression signatures reveal associations with psychiatric diseases. S1/2-/- mice display alterations in novelty induced activity, anxiety and curiosity. Moreover, mutant mice exhibit impaired working memory and deficits in prepulse inhibition resembling symptoms of psychiatric diseases. Network modeling indicates a connection between neural plasticity and clock genes, particularly for SHARP1 and PER1. Our findings support the hypothesis that abnormal sleep and certain (endo)phenotypes of psychiatric diseases may be caused by common mechanisms involving components of the molecular clock including SHARP1 and SHARP2.

The aryl hydrocarbon receptor: differential contribution to T helper 17 and T cytotoxic 17 cell development

The aryl hydrocarbon receptor (AhR) has been shown to be required for optimal Thelper (Th) 17 cell activation. Th17 cells provide immunity against extracellular pathogens and are implicated in autoimmune diseases. Herein, the role of the AhR in cytokine production by Th17, and by the analogous population of T cytotoxic (Tc)17 cells, has been examined. Lymph node Tc (CD8(+)) and Th (CD4(+)) cells were isolated by negative selection from naive AhR(+/-) and AhR(-/-) mice and polarised to Tc1/Th1 or Tc17/Th17 phenotypes with appropriate cytokines. Cell differentiation was assessed as a function of mRNA and protein (ELISA and flow cytometry) expression for interferon (IFN)-γ and for key Th17 cytokines. In AhR(+/-) mice, Th17 cells displayed an exclusive IL-17 profile, which was markedly inhibited by a selective AhR antagonist to levels observed in AhR knockout mice. Addition of the natural AhR agonist 6-formylindolo[3,2-b]carbazole (FICZ) markedly enhanced Th17 cell activity in the heterozygotes. In contrast, Tc17 cells polarised into 3 distinct subsets: producing either IL-17 or IFN-γ alone, or both cytokines. Blocking AhR was also detrimental to Tc17 development, with reduced responses recorded in AhR(-/-) mice and antagonist-mediated reduction of IL-17 expression in the heterozygotes. However, Tc17 cells were largely refractory to exogenous FICZ, presumably because Tc17 cells express baseline AhR mRNA, but unlike Th17 cells, there is no marked up-regulation during polarisation. Thus, Th17 cell development is more dependent upon AhR activation than is Tc17 cell development, suggesting that endogenous AhR ligands play a much greater role in driving Th17 cell responses.

Transplant restoration of spinal cord inhibitory controls ameliorates neuropathic itch

The transmission of pruritoceptive (itch) messages involves specific neural circuits within the spinal cord that are distinct from those that transmit pain messages. These itch-specific circuits are tonically regulated by inhibitory interneurons in the dorsal horn. Consistent with these findings, it has previously been reported that loss of GABAergic interneurons in mice harboring a deletion of the transcription factor Bhlhb5 generates a severe, nonremitting condition of chronic itch. Here, we tested the hypothesis that the neuropathic itch in BHLHB5-deficient animals can be treated by restoring inhibitory controls through spinal cord transplantation and integration of precursors of cortical inhibitory interneurons derived from the embryonic medial ganglionic eminence. We specifically targeted the transplants to segments of the spinal cord innervated by areas of the body that were most severely affected. BHLHB5-deficient mice that received transplants demonstrated a substantial reduction of excessive scratching and dramatic resolution of skin lesions. In contrast, the scratching persisted and skin lesions worsened over time in sham-treated mice. Together, these results indicate that cell-mediated restoration of inhibitory controls has potential as a powerful, cell-based therapy for neuropathic itch that not only ameliorates symptoms of chronic itch, but also may modify disease.

Endothelial HIF-2 mediates protection and recovery from ischemic kidney injury

The hypoxia-inducible transcription factors HIF-1 and HIF-2 mediate key cellular adaptions to hypoxia and contribute to renal homeostasis and pathophysiology; however, little is known about the cell type-specific functions of HIF-1 and HIF-2 in response to ischemic kidney injury. Here, we used a genetic approach to specifically dissect the roles of endothelial HIF-1 and HIF-2 in murine models of hypoxic kidney injury induced by ischemia reperfusion or ureteral obstruction. In both models, inactivation of endothelial HIF increased injury-associated renal inflammation and fibrosis. Specifically, inactivation of endothelial HIF-2α, but not endothelial HIF-1α, resulted in increased expression of renal injury markers and inflammatory cell infiltration in the postischemic kidney, which was reversed by blockade of vascular cell adhesion molecule-1 (VCAM1) and very late antigen-4 (VLA4) using monoclonal antibodies. In contrast, pharmacologic or genetic activation of HIF via HIF prolyl-hydroxylase inhibition protected wild-type animals from ischemic kidney injury and inflammation; however, these same protective effects were not observed in HIF prolyl-hydroxylase inhibitor-treated animals lacking endothelial HIF-2. Taken together, our data indicate that endothelial HIF-2 protects from hypoxia-induced renal damage and represents a potential therapeutic target for renoprotection and prevention of fibrosis following acute ischemic injury.

An optimized and simplified system of mouse embryonic stem cell cardiac differentiation for the assessment of differentiation modifiers

Generating cardiomyocytes from embryonic stem cells is an important technique for understanding cardiovascular development, the origins of cardiovascular diseases and also for providing potential reagents for cardiac repair. Numerous methods have been published but often are technically challenging, complex, and are not easily adapted to assessment of specific gene contributions to cardiac myocyte differentiation. Here we report the development of an optimized protocol to induce the differentiation of mouse embryonic stem cells to cardiac myocytes that is simplified and easily adapted for genetic studies. Specifically, we made four critical findings that distinguish our protocol: 1) mouse embryonic stem cells cultured in media containing CHIR99021 and PD0325901 to maintain pluripotency will efficiently form embryoid bodies containing precardiac mesoderm when cultured in these factors at a reduced dosage, 2) low serum conditions promote cardiomyocyte differentiation and can be used in place of commercially prepared StemPro nutrient supplement, 3) the Wnt inhibitor Dkk-1 is dispensable for efficient cardiac differentiation and 4) tracking differentiation efficiency may be done with surface expression of PDGFRα alone. In addition, cardiac mesodermal precursors generated by this system can undergo lentiviral infection to manipulate the expression of specific target molecules to assess effects on cardiac myocyte differentiation and maturation. Using this approach, we assessed the effects of CHF1/Hey2 on cardiac myocyte differentiation, using both gain and loss of function. Overexpression of CHF1/Hey2 at the cardiac mesoderm stage had no apparent effect on cardiac differentiation, while knockdown of CHF1/Hey2 resulted in increased expression of atrial natriuretic factor and connexin 43, suggesting an alteration in the phenotype of the cardiomyocytes. In summary we have generated a detailed and simplified protocol for generating cardiomyocytes from mES cells that is optimized for investigating factors that affect cardiac differentiation.

Hypoxia inducible factor-2α regulates the development of retinal astrocytic network by maintaining adequate supply of astrocyte progenitors

Here we investigate the role of hypoxia inducible factor (HIF)-2α in coordinating the development of retinal astrocytic and vascular networks. Three Cre mouse lines were used to disrupt floxed Hif-2α, including Rosa26^CreERT2, Tie2^Cre, and GFAP^Cre. Global Hif-2α disruption by Rosa26^CreERT2 led to reduced astrocytic and vascular development in neonatal retinas, whereas endothelial disruption by Tie2^Cre had no apparent effects. Hif-2α deletion in astrocyte progenitors by GFAP^Cre significantly interfered with the development of astrocytic networks, which failed to reach the retinal periphery and were incapable of supporting vascular development. Perplexingly, the abundance of strongly GFAP⁺ mature astrocytes transiently increased at P0 before they began to lag behind the normal controls by P3. Pax2⁺ and PDGFRα⁺ astrocytic progenitors and immature astrocytes were dramatically diminished at all stages examined. Despite decreased number of astrocyte progenitors, their proliferation index or apoptosis was not altered. The above data can be reconciled by proposing that HIF-2α is required for maintaining the supply of astrocyte progenitors by slowing down their differentiation into non-proliferative mature astrocytes. HIF-2α deficiency in astrocyte progenitors may accelerate their differentiation into astrocytes, a change which greatly interferes with the replenishment of astrocyte progenitors due to insufficient time for proliferation. Rapidly declining progenitor supply may lead to premature cessation of astrocyte development. Given that HIF-2α protein undergoes oxygen dependent degradation, an interesting possibility is that retinal blood vessels may regulate astrocyte differentiation through their oxygen delivery function. While our findings support the consensus that retinal astrocytic template guides vascular development, they also raise the possibility that astrocytic and vascular networks may mutually regulate each other's development, mediated at least in part by HIF-2α.

Birth of cone bipolar cells, but not rod bipolar cells, is associated with existing RGCs

Retinal ganglion cells (RGCs) play important roles in retinogenesis. They are required for normal retinal histogenesis and retinal cell number balance. Developmental RGC loss is typically characterized by initial retinal neuronal number imbalance and subsequent loss of retinal neurons. However, it is not clear whether loss of a specific non-RGC cell type in the RGC-depleted retina is due to reduced cell production or subsequent degeneration. Taking advantage of three knockout mice with varying degrees of RGC depletion, we re-examined bipolar cell production in these retinas from various aspects. Results show that generation of the cone bipolar cells is correlated with the existing number of RGCs. However, generation of the rod bipolar cells is unaffected by RGC shortage. Results report the first observation that RGCs selectively influence the genesis of subsequent retinal cell types.

Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration

Brain aging is associated with diminished circadian clock output and decreased expression of the core clock proteins, which regulate many aspects of cellular biochemistry and metabolism. The genes encoding clock proteins are expressed throughout the brain, though it is unknown whether these proteins modulate brain homeostasis. We observed that deletion of circadian clock transcriptional activators aryl hydrocarbon receptor nuclear translocator-like (Bmal1) alone, or circadian locomotor output cycles kaput (Clock) in combination with neuronal PAS domain protein 2 (Npas2), induced severe age-dependent astrogliosis in the cortex and hippocampus. Mice lacking the clock gene repressors period circadian clock 1 (Per1) and period circadian clock 2 (Per2) had no observed astrogliosis. Bmal1 deletion caused the degeneration of synaptic terminals and impaired cortical functional connectivity, as well as neuronal oxidative damage and impaired expression of several redox defense genes. Targeted deletion of Bmal1 in neurons and glia caused similar neuropathology, despite the retention of intact circadian behavioral and sleep-wake rhythms. Reduction of Bmal1 expression promoted neuronal death in primary cultures and in mice treated with a chemical inducer of oxidative injury and striatal neurodegeneration. Our findings indicate that BMAL1 in a complex with CLOCK or NPAS2 regulates cerebral redox homeostasis and connects impaired clock gene function to neurodegeneration.

Paraventricular nucleus Sim1 neuron ablation mediated obesity is resistant to high fat diet

Single minded 1 (SIM1) is a transcription factor involved in brain patterning and control of energy balance. In humans, haploinsufficiency of SIM1 causes early-onset obesity. Mice deficient in the homologous gene, SIM1, also exhibit early onset obesity and increased sensitivity to a high fat diet. SIM1 is expressed in several areas of the brain implicated in control of energy balance including the paraventricular nucleus (PVN), the supraoptic nucleus (SON), the medial amygdala and nucleus of the lateral olfactory tract. We have previously shown that mice with global Sim1 neuron ablation exhibit obesity with hyperphagia as the primary defect. The PVN has a critical role in feeding and in high-fat appetite, thus, we sought to determine the effect of Sim1 neuron ablation limited to the PVN. We achieved PVN-SIM1 limited ablation through stereotactic injection of diphtheria toxin into the PVN of Sim1Cre-iDTR mice. The specificity of this ablation was confirmed by immunohistochemistry and quantitative real time PCR of the PVN, supraoptic nucleus and the amygdala. Mice with PVN Sim1 neuron ablation, similar to mice with global Sim1 neuron ablation, exhibit early onset obesity with hyperphagia as the primary defect. However, PVN-Sim1 neuron ablated mice have a decreased response to fasting-induced hyperphagia. Consistent with this decrement, PVN-Sim1 neuron ablated mice have a decreased hyperphagic response to PVN injection of agouti-related peptide (AgRP). When PVN-Sim1 neuron ablated mice are placed on a high fat diet, surprisingly, their intake decreases and they actually lose weight. When allowed ad lib access to high fat diet and normal chow simultaneously, PVN-Sim1 neuron ablated mice exhibit overall decreased intake. That is, in PVN-Sim1 neuron ablated mice, access to fat suppresses overall appetite.

Differential influences of the aryl hydrocarbon receptor on Th17 mediated responses in vitro and in vivo

The aryl hydrocarbon receptor (AhR) has been attributed with anti-inflammatory effects in the development of pathological immune responses leading to experimental autoimmune encephalomyelitis (EAE) via the induction of regulatory T cells. In agreement with previously published findings, we find that TCDD administration confers protection from EAE, however, this immuno-modulatory effect was not the consequence of de novo Treg generation, but the inhibition of Th17 cell differentiation. Systemic application of FICZ at the time of immunization also reduced EAE pathology albeit to a lesser degree than TCDD. In vitro Th17 differentiation in the presence of AhR agonists, including TCDD, promoted IL-17 and IL-22 expression, but did not induce Treg differentiation. AhR affinity influenced the amounts of IL-17 and IL-22 protein that was secreted by Th17 cells, but did not seem to affect susceptibility to EAE in vivo. Making use of conditional AhR-deficient mice, we show that the anti-inflammatory effect of TCDD depends on AhR activation in both T cells and dendritic cells, further emphasising the ability of TCDD to interfere with T effector cell differentiation in vivo. The dichotomy between the in vivo and in vitro effects of AhR reveals the complexity of the AhR pathway, which has the capacity of affecting different AhR-expressing cell types involved in mounting immune responses, thus participating in defining their outcome.

Tryptophan catabolites from microbiota engage aryl hydrocarbon receptor and balance mucosal reactivity via interleukin-22

Endogenous tryptophan (Trp) metabolites have an important role in mammalian gut immune homeostasis, yet the potential contribution of Trp metabolites from resident microbiota has never been addressed experimentally. Here, we describe a metabolic pathway whereby Trp metabolites from the microbiota balance mucosal reactivity in mice. Switching from sugar to Trp as an energy source (e.g., under conditions of unrestricted Trp availability), highly adaptive lactobacilli are expanded and produce an aryl hydrocarbon receptor (AhR) ligand-indole-3-aldehyde-that contributes to AhR-dependent Il22 transcription. The resulting IL-22-dependent balanced mucosal response allows for survival of mixed microbial communities yet provides colonization resistance to the fungus Candida albicans and mucosal protection from inflammation. Thus, the microbiota-AhR axis might represent an important strategy pursued by coevolutive commensalism for fine tuning host mucosal reactivity contingent on Trp catabolism.

Ectopic Runx1 expression rescues Tal-1-deficiency in the generation of primitive and definitive hematopoiesis

The transcription factors SCL/Tal-1 and AML1/Runx1 control the generation of pluripotent hematopoietic stem cells (pHSC) and, thereby, primitive and definitive hematopoiesis, during embryonic development of the mouse from mesoderm. Thus, Runx1-deficient mice generate primitive, but not definitive hematopoiesis, while Tal-1-deficient mice are completely defective. Primitive as well as definitive hematopoiesis can be developed "in vitro" from embryonic stem cells (ESC). We show that wild type, as well as Tal-1(-/-) and Runx1(-/-) ESCs, induced to differentiation, all expand within 5 days to comparable numbers of Flk1(+) mesodermal cells. While wild type ESCs further differentiate to primitive and definitive erythrocytes, to c-fms(+)Gr1(+)Mac1(+) myeloid cells, and to B220(+)CD19(+) B- and CD4(+)/CD8(+) T-lymphoid cells, Runx1(-/-) ESCs, as expected, only develop primitive erythrocytes, and Tal-1(-/-) ESCs do not generate any hematopoietic cells. Retroviral transduction with Runx1 of Runx1(-/-) ESCs, differentiated for 4 days to mesoderm, rescues definitive erythropoiesis, myelopoiesis and lymphopoiesis, though only with 1-10% of the efficiencies of wild type ESC hematopoiesis. Surprisingly, Tal-1(-/-) ESCs can also be rescued at comparably low efficiencies to primitive and definitive erythropoiesis, and to myelopoiesis and lymphopoiesis by retroviral transduction with Runx1. These results suggest that Tal-1 expression is needed to express Runx1 in mesoderm, and that ectopic expression of Runx1 in mesoderm is sufficient to induce primitive as well as definitive hematopoiesis in the absence of Tal-1. Retroviral transduction of "in vitro" differentiating Tal-1(-/-) and Runx1(-/-) ESCs should be a useful experimental tool to probe selected genes for activities in the generation of hematopoietic progenitors "in vitro", and to assess the potential transforming activities in hematopoiesis of mutant forms of Tal-1 and Runx1 from acute myeloid leukemia and related tumors.

Myeloid cell HIF-1α regulates asthma airway resistance and eosinophil function

Hypoxia-inducible factor (HIF)-1α is a master regulator of inflammatory activities of myeloid cells, including neutrophils and macrophages. These studies examine the role of myeloid cell HIF-1α in regulating asthma induction and pathogenesis, and for the first time, evaluate the roles of HIF-1α and HIF-2α in the chemotactic properties of eosinophils, the myeloid cells most associated with asthma. Wild-type (WT) and myeloid cell-specific HIF-1α knockout (KO) C57BL/6 mice were studied in an ovalbumin (OVA) model of asthma. Administration of the pharmacological HIF-1α antagonist YC-1 was used to corroborate findings from the genetic model. WT, HIF-1α, and HIF-2α KO eosinophils underwent in vitro chemotaxis assays. We found that deletion of HIF-1α in myeloid cells and systemic treatment with YC-1 during asthma induction decreased airway hyperresponsiveness (AHR). Deletion of HIF-1α in myeloid cells in OVA-induced asthma also reduced eosinophil infiltration, goblet cell hyperplasia, and levels of cytokines IL-4, IL-5, and IL-13 in the lung. HIF-1α inhibition with YC-1 during asthma induction decreased eosinophilia in bronchoalveolar lavage, lung parenchyma, and blood, as well as decreased total lung inflammation, IL-5, and serum OVA-specific IgE levels. Deletion of HIF-1α in eosinophils decreased their chemotaxis, while deletion of the isoform HIF-2α led to increased chemotaxis. This work demonstrates that HIF-1α in myeloid cells plays a role in asthma pathogenesis, particularly in AHR development. Additionally, treatment with HIF-1α inhibitors during asthma induction decreases AHR and eosinophilia. Finally, we show that HIF-1α and HIF-2α regulate eosinophil migration in opposing ways.

Requirement and functional redundancy of Ib subgroup bHLH proteins for iron deficiency responses and uptake in Arabidopsis thaliana

The Ib subgroup of the bHLH gene family in Arabidopsis contains four members (AtbHLH38, AtbHLH39, AtbHLH100, and AtbHLH101). AtbHLH38 and AtbHLH39 were previously confirmed to interact with FER-like iron deficiency induced transcription factor (FIT), directly functioning in activation of the expression of ferric-chelate reductase FRO2 and high-affinity ferrous iron transporter IRT1. In this work, we characterized the functions of AtbHLH100 and AtbHLH101 in the regulation of the iron-deficiency responses and uptake. Yeast two-hybrid analysis and bimolecular fluorescence complementation assay demonstrated that both AtbHLH100 and AtbHLH101 could interact with FIT. Dual expression of either AtbHLH100 or AtbHLH101 with FIT in yeast cells activated the GUS expression driven by promoters of FRO2 and IRT1. The plants overexpressing FIT together with AtbHLH101 showed constitutive expression of FRO2 and IRT1 in roots, and accumulated more iron in shoots. Further, the single, double, and triple knockout mutants of AtbHLH38, AtbHLH39, AtbHLH100, and AtbHLH101 were generated and characterized. The FRO2 and IRT1 expression in roots and the iron content in shoots were more drastically decreased in the triple knockout mutant of AtbHLH39, AtbHLH100, and AtbHLH101 than that of the other available double and triple mutants of the four genes. Comparison of the physiological responses as well as the expression of FRO2 and IRT1 in the multiple knockout mutants under iron deficiency revealed that AtbHLH100, AtbHLH38, AtbHLH101, and AtbHLH39 played the gradually increased important role in the iron-deficiency responses and uptake. Taken all together, we conclude that the four Ib subgroup bHLH proteins are required and possess redundant functions with differential significance for activation of iron-deficiency responses and uptake in Arabidopsis.

Apoptosis regulates ipRGC spacing necessary for rods and cones to drive circadian photoentrainment

The retina consists of ordered arrays of individual types of neurons for processing vision. Here, we show that such order is necessary for intrinsically photosensitive retinal ganglion cells (ipRGCs) to function as irradiance detectors. We found that during development, ipRGCs undergo proximity-dependent Bax-mediated apoptosis. Bax mutant mice exhibit disrupted ipRGC spacing and dendritic stratification with an increase in abnormally localized synapses. ipRGCs are the sole conduit for light input to circadian photoentrainment, and either their melanopsin-based photosensitivity or ability to relay rod/cone input is sufficient for circadian photoentrainment. Remarkably, the disrupted ipRGC spacing does not affect melanopsin-based circadian photoentrainment but severely impairs rod/cone-driven photoentrainment. We demonstrate reduced rod/cone-driven cFos activation and electrophysiological responses in ipRGCs, suggesting that impaired synaptic input to ipRGCs underlies the photoentrainment deficits. Thus, for irradiance detection, developmental apoptosis is necessary for the spacing and connectivity of ipRGCs that underlie their functioning within a neural network.

Expression at the imprinted dlk1-gtl2 locus is regulated by proneural genes in the developing telencephalon

Imprinting is an epigenetic mechanism that restrains the expression of about 100 genes to one allele depending on its parental origin. Several imprinted genes are implicated in neurodevelopmental brain disorders, such as autism, Angelman, and Prader-Willi syndromes. However, how expression of these imprinted genes is regulated during neural development is poorly understood. Here, using single and double KO animals for the transcription factors Neurogenin2 (Ngn2) and Achaete-scute homolog 1 (Ascl1), we found that the expression of a specific subset of imprinted genes is controlled by these proneural genes. Using in situ hybridization and quantitative PCR, we determined that five imprinted transcripts situated at the Dlk1-Gtl2 locus (Dlk1, Gtl2, Mirg, Rian, Rtl1) are upregulated in the dorsal telencephalon of Ngn2 KO mice. This suggests that Ngn2 influences the expression of the entire Dlk1-Gtl2 locus, independently of the parental origin of the transcripts. Interestingly 14 other imprinted genes situated at other imprinted loci were not affected by the loss of Ngn2. Finally, using Ngn2/Ascl1 double KO mice, we show that the upregulation of genes at the Dlk1-Gtl2 locus in Ngn2 KO animals requires a functional copy of Ascl1. Our data suggest a complex interplay between proneural genes in the developing forebrain that control the level of expression at the imprinted Dlk1-Gtl2 locus (but not of other imprinted genes). This raises the possibility that the transcripts of this selective locus participate in the biological effects of proneural genes in the developing telencephalon.

The bHLH transcription factor Tcf21 is required for lineage-specific EMT of cardiac fibroblast progenitors

The basic helix-loop-helix (bHLH) family of transcription factors orchestrates cell-fate specification, commitment and differentiation in multiple cell lineages during development. Here, we describe the role of a bHLH transcription factor, Tcf21 (epicardin/Pod1/capsulin), in specification of the cardiac fibroblast lineage. In the developing heart, the epicardium constitutes the primary source of progenitor cells that form two cell lineages: coronary vascular smooth muscle cells (cVSMCs) and cardiac fibroblasts. Currently, there is a debate regarding whether the specification of these lineages occurs early in the formation of the epicardium or later after the cells have entered the myocardium. Lineage tracing using a tamoxifen-inducible Cre expressed from the Tcf21 locus demonstrated that the majority of Tcf21-expressing epicardial cells are committed to the cardiac fibroblast lineage prior to initiation of epicardial epithelial-to-mesenchymal transition (EMT). Furthermore, Tcf21 null hearts fail to form cardiac fibroblasts, and lineage tracing of the null cells showed their inability to undergo EMT. This is the first report of a transcription factor essential for the development of cardiac fibroblasts. We demonstrate a unique role for Tcf21 in multipotent epicardial progenitors, prior to the process of EMT that is essential for cardiac fibroblast development.