Evidence that TGF beta may directly modulate POMC mRNA expression in the female rat arcuate nucleus

Developmental genes controlling neural circuit formation are expressed in the early postnatal hypothalamus and cellular lining of the third ventricle

The arcuate nucleus of the hypothalamus is central in the regulation of body weight homeostasis through its ability to sense peripheral metabolic signals and relay them, through neural circuits, to other brain areas, ultimately affecting physiological and behavioural changes. The early postnatal development of these neural circuits is critical for normal body weight homeostasis, such that perturbations during this critical period can lead to obesity. The role for peripheral regulators of body weight homeostasis, including leptin, insulin and ghrelin, in this postnatal development is well described, yet some of the fundamental processes underpinning axonal and dendritic growth remain unclear. Here, we hypothesised that molecules known to regulate axonal and dendritic growth processes in other areas of the developing brain would be expressed in the postnatal arcuate nucleus and/or target nuclei where they would function to mediate the development of this circuitry. Using state-of-the-art RNAscope^® technology, we have revealed the expression patterns of genes encoding Dcc/Netrin-1, Robo1/Slit1 and Fzd5/Wnt5a receptor/ligand pairs in the early postnatal mouse hypothalamus. We found that individual genes had unique expression patterns across developmental time in the arcuate nucleus, paraventricular nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, dorsomedial nucleus of the hypothalamus, median eminence and, somewhat unexpectedly, the third ventricle epithelium. These observations indicate a number of new molecular players in the development of neural circuits regulating body weight homeostasis, as well as novel molecular markers of tanycyte heterogeneity.

Obesity-associated extracellular mtDNA activates central TGFβ pathway to cause blood pressure increase

Hypothalamic inflammation was recently found to mediate obesity-related hypertension, but the responsible upstream mediators remain unexplored. In this study, we show that dietary obesity is associated with extracellular release of mitochondrial DNA (mtDNA) into the cerebrospinal fluid and that central delivery of mtDNA mimics transforming growth factor-β (TGFβ) excess to activate downstream signaling pathways. Physiological study reveals that central administration of mtDNA or TGFβ is sufficient to cause hypertension in mice. Knockout of the TGFβ receptor in proopiomelanocortin neurons counteracts the hypertensive effect of not only TGFβ but also mtDNA excess, while the hypertensive action of central mtDNA can be blocked pharmacologically by a TGFβ receptor antagonist or genetically by TGFβ receptor knockout. Finally, we confirm that obesity-induced hypertension can be reversed through central treatment with TGFβ receptor antagonist. In conclusion, circulating mtDNA in the brain employs neural TGFβ pathway to mediate a central inflammatory mechanism of obesity-related hypertension.

Variable proopiomelanocortin expression in tanycytes of the adult rat hypothalamus and pituitary stalk

It is generally believed that proopiomelanocortin (POMC) is expressed exclusively by neurons in the adult rodent brain. Unbeknownst to most researchers, however, Pomc in situ hybridization studies in the rat show specific labeling in the ventral wall of the hypothalamic third ventricle, which is formed by specialized ependymal cells, called tanycytes. Here we characterized this non-neuronal POMC expression in detail using in situ hybridization and immunohistochemical techniques, and report two unique characteristics. First, POMC mRNA and precursor protein expression in non-neuronal cells varies to a great degree as to the extent and abundance of expression. In brains with low-level expression, POMC mRNA and protein was largely confined to a population of tanycytes within the infundibular stalk/caudal median eminence, termed here γ tanycytes, and a subset of closely located β and α2 tanycytes. In brains with high-level expression, POMC mRNA and protein was observed in the vast majority of α2, β, and γ tanycytes. This variability was observed in both adult males and females; of 41 rats between 8 and 15 weeks of age, 17 had low-, 9 intermediate-, and 15 high-level POMC expression in tanycytes. Second, unlike other known POMC-expressing cells, tanycytes rarely contained detectable levels of adrenocorticotropin or α-melanocyte-stimulating hormone. The results indicate either a dynamic spatiotemporal pattern whereby low and high POMC syntheses in tanycytes occur periodically in each brain, or marked interindividual differences that may persist throughout adulthood. Future studies are required to examine these possibilities and elucidate the physiologic importance of POMC in tanycytes. J. Comp. Neurol. 525:411-441, 2017. © 2016 Wiley Periodicals, Inc.

Obesity- and aging-induced excess of central transforming growth factor-β potentiates diabetic development via an RNA stress response

The brain, in particular the hypothalamus, plays a role in regulating glucose homeostasis; however, it remains unclear whether this organ is causally and etiologically involved in the development of diabetes. Here, we found that hypothalamic transforming growth factor-β (TGF-β) production is excessive under conditions of not only obesity but also aging, which are two general etiological factors of type 2 diabetes. Pharmacological and genetic approaches revealed that central TGF-β excess caused hyperglycemia and glucose intolerance independent of a change in body weight. Further, using cell-specific genetic analyses in vivo, we found that astrocytes and proopiomelanocortin neurons are responsible for the production and prodiabetic effect of central TGF-β, respectively. Mechanistically, TGF-β excess induced a hypothalamic RNA stress response, resulting in accelerated mRNA decay of IκBα, an inhibitor of proinflammatory nuclear factor-κB. These results reveal an atypical, mRNA metabolism-driven hypothalamic nuclear factor-κB activation, a mechanism that links obesity as well as aging to hypothalamic inflammation and ultimately to type 2 diabetes.

Strong exercise stress exacerbates dermatitis in atopic model mice, NC/Nga mice, while proper exercise reduces it

Atopic dermatitis is well known to exacerbate by stress. How the influence of exercise stress on the skin symptoms in patients with atopic dermatitis has not been clarified. The purpose of our research is to investigate how different strength of exercise stress acts on atopic dermatitis. Specific pathogen-free (SPF) and conventional NC/Nga male mice were used for the experiments. Conventional mice but not SPF group spontaneously develop dermal symptom similar to that of patients with atopic dermatitis at their age of 7 weeks. They were given two types of stress, mild (20 m/min for 60 min) or strong exercise (25 m/min for 90 min), using a treadmill four times per day. The dermal symptom of the conventional group was strongly exacerbated by strong exercise but ameliorated by mild exercise. Under the standard experimental conditions, plasma concentrations of α-melanocyte-stimulating hormone (α-MSH), transforming growth factor-β (TGF-β) and substance P in conventional mice increased markedly with concomitant exacerbation of the symptom. The plasma concentrations of these proteins elevated after strong exercise but decreased after mild exercise. Under the conventional conditions, plasma levels of β-endorphin increased with time by some mechanisms enhanced by the mild exercise. These observations suggested that exercise-induced stress significantly affect the symptom of atopic dermatitis in a pivotal manner depending on the plasma levels of TGF-β, α-MSH, substance P and β-endorphin.

BAMBI (bone morphogenetic protein and activin membrane-bound inhibitor) reveals the involvement of the transforming growth factor-beta family in pain modulation

Transforming growth factors-beta (TGF-betas) signal through type I and type II serine-threonine kinase receptor complexes. During ligand binding, type II receptors recruit and phosphorylate type I receptors, triggering downstream signaling. BAMBI [bone morphogenetic protein (BMP) and activin membrane-bound inhibitor] is a transmembrane pseudoreceptor structurally similar to type I receptors but lacks the intracellular kinase domain. BAMBI modulates negatively pan-TGF-beta family signaling; therefore, it can be used as an instrument for unraveling the roles of these cytokines in the adult CNS. BAMBI is expressed in regions of the CNS involved in pain transmission and modulation. The lack of BAMBI in mutant mice resulted in increased levels of TGF-beta signaling activity, which was associated with attenuation of acute pain behaviors, regardless of the modality of the stimuli (thermal, mechanical, chemical/inflammatory). The nociceptive hyposensitivity exhibited by BAMBI(-/-) mice was reversed by the opioid antagonist naloxone. Moreover, in a model of chronic neuropathic pain, the allodynic responses of BAMBI(-/-) mice also appeared attenuated through a mechanism involving delta-opioid receptor signaling. Basal mRNA and protein levels of precursor proteins of the endogenous opioid peptides proopiomelanocortin (POMC) and proenkephalin (PENK) appeared increased in the spinal cords of BAMBI(-/-). Transcript levels of TGF-betas and their intracellular effectors correlated directly with genes encoding opioid peptides, whereas BAMBI correlated inversely. Furthermore, incubation of spinal cord explants with activin A or BMP-7 increased POMC and/or PENK mRNA levels. Our findings identify TGF-beta family members as modulators of acute and chronic pain perception through the transcriptional regulation of genes encoding the endogenous opioids.

Induction of transforming growth factor-β1 by basic fibroblast growth factor in rat C6 glioma cells and astrocytes is mediated by MEK/ERK signaling and AP-1 activation

Basic fibroblast growth factor (bFGF) and transforming growth factor-beta1 (TGF-beta1) play an important role in proliferation, differentiation, and survival of malignant gliomas and in normal glial cell biology. Because of these critical roles, potential interactions between these key growth factors were investigated. We previously demonstrated that bFGF potently stimulates TGF-beta1 release from rat glioma cells. The purpose of the present study was to elucidate the mechanism(s) of this regulatory effect, establish its functional importance, and examine whether it extends to nontransformed rat hypothalamic astrocytes (RHA). The results revealed that RHA express the high-affinity FGF(1-4) receptors, and similarly to glioma cells, bFGF stimulated TGF-beta1 release in an isoform-specific manner. A mediatory role for ERK signaling in bFGF-induced TGF-beta release was suggested by the fact that MEK1 inhibition prevented this effect. Additionally, bFGF enhanced MEK1/2 phosphorylation and ERK activation/nuclear translocation, which culminated in increased activity of AP-1-mediated gene transcription. bFGF markedly induced TGF-beta1 mRNA levels in an isoform-specific manner, an effect that was dependent on MEK/ERK/AP-1 signaling. Functionally, bFGF-induced proliferation of glioma cells was attenuated by MEK/ERK inhibition or immunoneutralization of TGF-beta1, suggesting that this pathway may have important implications for brain tumor progression.

Expression of the transcriptional coactivator CITED1 in the adult and developing murine brain

The transcription coactivator CITED1 is an important mediator of transcriptional events regulated by estrogen or TGF-beta. We used in situ hybridization to delineate the distribution of CITED1 mRNA in the adult and developing murine brain and found robust CITED1 expression in ventral hypothalamus and midbrain raphe. The distribution of CITED1 in these regions overlapped the reported expression of estrogen receptors alpha and beta. Less intense expression of CITED1 was also evident in medial preoptic area, subfornical organ, thalamus and cerebral cortex. CITED1 mRNA in the arcuate nucleus (an area of active transcriptional modulation by TGF-beta) was evident in postmigratory neurons as early as embryonic day 16. Expression of CITED1 in arcuate continued throughout postnatal development. CITED1 in developing cerebellum was first evident in external granule cells and was transiently expressed in the Purkinje cell/granule cell layer in a temporal pattern similar to estrogen receptor-beta. The spatial and temporal distribution of CITED1 mRNA reported here is consistent with a role for CITED1 in the modulation of transcriptional events mediated by steroid hormone and cytokine signaling pathways.

Bone morphogenic protein (Smad)-mediated repression of proopiomelanocortin transcription by interference with Pitx/Tpit activity

The signaling molecules bone morphogenic protein (BMP) 4 and 2 have been implicated in early organogenesis and cell differentiation of the pituitary. However, the use of different experimental paradigms has led to conflicting interpretations with regard to the action of these factors on differentiation of corticotroph cells and on expression of the proopiomelanocortin (POMC) gene. We have now directly assessed the action of BMP signaling on POMC expression and found that BMP4 represses POMC mRNA levels and promoter activity. This repression appears to be dependent on the classical BMP signaling pathway that involves the activin-like kinase 3/6 receptors and the Smad1/4 transcription factors. The repression is reversed by overexpression of the inhibitory Smads, Smad6 or Smad7. Collectively, the evidence suggests that autocrine BMP signaling may be acting upon AtT-20 cells to set the level of POMC expression. Upon BMP4 stimulation, activated phospho-Smad1 is recruited to the POMC promoter, where it apparently acts through interactions with the Pitx and Tpit transcription factors. It is postulated that these interactions interfere with the transcriptional activity of Pitx and/or Tpit, thus resulting in transcriptional repression.