The FGF23 coreceptor αKlotho (αKL) is expressed as a membrane-bound protein (mKL) that forms heteromeric complexes with FGF receptors (FGFRs) to initiate intracellular signaling. It also circulates as an endoproteolytic cleavage product of mKL (cKL). Previously, a patient with increased plasma cKL as the result of a translocation [t(9;13)] in the αKLOTHO (KL) gene presented with rickets and a complex endocrine profile, including paradoxically elevated plasma FGF23, despite hypophosphatemia. The goal of this study was to test whether cKL regulates phosphate handling through control of FGF23 expression. To increase cKL levels, mice were treated with an adeno-associated virus producing cKL. The treated groups exhibited dose-dependent hypophosphatemia and hypocalcemia, with markedly elevated FGF23 (38 to 456 fold). The animals also manifested fractures, reduced bone mineral content, expanded growth plates, and severe osteomalacia, with highly increased bone Fgf23 mRNA (>150 fold). cKL activity in vitro was specific for interactions with FGF23 and was FGFR dependent. These results demonstrate that cKL potently stimulates FGF23 production in vivo, which phenocopies the KL translocation patient and metabolic bone syndromes associated with elevated FGF23. These findings have important implications for the regulation of αKL and FGF23 in disorders of phosphate handling and biomineralization.
Rosamund C. Smith, Linda M. O’Bryan, Emily G. Farrow, Lelia J. Summers, Erica L. Clinkenbeard, Jessica L. Roberts, Taryn A. Cass, Joy Saha, Carol Broderick, Y. Linda Ma, Qing Qiang Zeng, Alexei Kharitonenkov, Jonathan M. Wilson, Qianxu Guo, Haijun Sun, Matthew R. Allen, David B. Burr, Matthew D. Breyer, Kenneth E. White
Src homology 2 B adapter protein 1 (SH2B1) modulates signaling by a variety of ligands that bind to receptor tyrosine kinases or JAK-associated cytokine receptors, including leptin, insulin, growth hormone (GH), and nerve growth factor (NGF). Targeted deletion of Sh2b1 in mice results in increased food intake, obesity, and insulin resistance, with an intermediate phenotype seen in heterozygous null mice on a high-fat diet. We identified SH2B1 loss-of-function mutations in a large cohort of patients with severe early-onset obesity. Mutation carriers exhibited hyperphagia, childhood-onset obesity, disproportionate insulin resistance, and reduced final height as adults. Unexpectedly, mutation carriers exhibited a spectrum of behavioral abnormalities that were not reported in controls, including social isolation and aggression. We conclude that SH2B1 plays a critical role in the control of human food intake and body weight and is implicated in maladaptive human behavior.
Michael E. Doche, Elena G. Bochukova, Hsiao-Wen Su, Laura R. Pearce, Julia M. Keogh, Elana Henning, Joel M. Cline, Anne Dale, Tim Cheetham, Inês Barroso, Lawrence S. Argetsinger, Stephen O’Rahilly, Liangyou Rui, Christin Carter-Su, I. Sadaf Farooqi
The endothelium regulates vascular homeostasis, and endothelial dysfunction is a proximate event in the pathogenesis of atherothrombosis. Stimulation of the endothelium with proinflammatory cytokines or exposure to hemodynamic-induced disturbed flow leads to a proadhesive and prothrombotic phenotype that promotes atherothrombosis. In contrast, exposure to arterial laminar flow induces a gene program that confers a largely antiadhesive, antithrombotic effect. The molecular basis for this differential effect on endothelial function remains poorly understood. While recent insights implicate Kruppel-like factors (KLFs) as important regulators of vascular homeostasis, the in vivo role of these factors in endothelial biology remains unproven. Here, we show that endothelial KLF4 is an essential determinant of atherogenesis and thrombosis. Using in vivo EC-specific KLF4 overexpression and knockdown murine models, we found that KLF4 induced an antiadhesive, antithrombotic state. Mechanistically, we demonstrated that KLF4 differentially regulated pertinent endothelial targets via competition for the coactivator p300. These observations provide cogent evidence implicating endothelial KLFs as essential in vivo regulators of vascular function in the adult animal.
Guangjin Zhou, Anne Hamik, Lalitha Nayak, Hongmei Tian, Hong Shi, Yuan Lu, Nikunj Sharma, Xudong Liao, Andrew Hale, Lauren Boerboom, Ryan E. Feaver, Huiyun Gao, Amar Desai, Alvin Schmaier, Stanton L. Gerson, Yunmei Wang, G. Brandon Atkins, Brett R. Blackman, Daniel I. Simon, Mukesh K. Jain
Congenital diarrheal disorders (CDDs) are a collection of rare, heterogeneous enteropathies with early onset and often severe outcomes. Here, we report a family of Ashkenazi Jewish descent, with 2 out of 3 children affected by CDD. Both affected children presented 3 days after birth with severe, intractable diarrhea. One child died from complications at age 17 months. The second child showed marked improvement, with resolution of most symptoms at 10 to 12 months of age. Using exome sequencing, we identified a rare splice site mutation in the DGAT1 gene and found that both affected children were homozygous carriers. Molecular analysis of the mutant allele indicated a total loss of function, with no detectable DGAT1 protein or activity produced. The precise cause of diarrhea is unknown, but we speculate that it relates to abnormal fat absorption and buildup of DGAT substrates in the intestinal mucosa. Our results identify DGAT1 loss-of-function mutations as a rare cause of CDDs. These findings prompt concern for DGAT1 inhibition in humans, which is being assessed for treating metabolic and other diseases.
Joel T. Haas, Harland S. Winter, Elaine Lim, Andrew Kirby, Brendan Blumenstiel, Matthew DeFelice, Stacey Gabriel, David Branski, Carrie A. Grueter, Mauro S. Toporovski, Tobias C. Walther, Mark J. Daly, Robert V. Farese Jr.
Cardiac natriuretic peptides (NP) are major activators of human fat cell lipolysis and have recently been shown to control brown fat thermogenesis. Here, we investigated the physiological role of NP on the oxidative metabolism of human skeletal muscle. NP receptor type A (NPRA) gene expression was positively correlated to mRNA levels of PPARγ coactivator-1α (PGC1A) and several oxidative phosphorylation (OXPHOS) genes in human skeletal muscle. Further, the expression of NPRA, PGC1A, and OXPHOS genes was coordinately upregulated in response to aerobic exercise training in human skeletal muscle. In human myotubes, NP induced PGC-1α and mitochondrial OXPHOS gene expression in a cyclic GMP–dependent manner. NP treatment increased OXPHOS protein expression, fat oxidation, and maximal respiration independent of substantial changes in mitochondrial proliferation and mass. Treatment of myotubes with NP recapitulated the effect of exercise training on muscle fat oxidative capacity in vivo. Collectively, these data show that activation of NP signaling in human skeletal muscle enhances mitochondrial oxidative metabolism and fat oxidation. We propose that NP could contribute to exercise training–induced improvement in skeletal muscle fat oxidative capacity in humans.
Stefan Engeli, Andreas L. Birkenfeld, Pierre-Marie Badin, Virginie Bourlier, Katie Louche, Nathalie Viguerie, Claire Thalamas, Emilie Montastier, Dominique Larrouy, Isabelle Harant, Isabelle de Glisezinski, Stefanie Lieske, Julia Reinke, Bibiana Beckmann, Dominique Langin, Jens Jordan, Cedric Moro
Current therapies directed at controlling vascular abnormalities in cancers and neovascular eye diseases target VEGF and can slow the progression of these diseases. While the critical role of VEGF in development has been well described, the function of locally synthesized VEGF in the adult eye is incompletely understood. Here, we show that conditionally knocking out Vegfa in adult mouse retinal pigmented epithelial (RPE) cells, which regulate retinal homeostasis, rapidly leads to vision loss and ablation of the choriocapillaris, the major blood supply for the outer retina and photoreceptor cells. This deletion also caused rapid dysfunction of cone photoreceptors, the cells responsible for fine visual acuity and color vision. Furthermore, Vegfa deletion showed significant downregulation of multiple angiogenic genes in both physiological and pathological states, whereas the deletion of the upstream regulatory transcriptional factors HIFs did not affect the physiological expressions of angiogenic genes. These results suggest that endogenous VEGF provides critical trophic support necessary for retinal function. Targeting factors upstream of VEGF, such as HIFs, may be therapeutically advantageous compared with more potent and selective VEGF antagonists, which may have more off-target inhibitory trophic effects.
Toshihide Kurihara, Peter D. Westenskow, Stephen Bravo, Edith Aguilar, Martin Friedlander
Although endoplasmic reticulum (ER) stress is a pathologic mechanism in a variety of chronic diseases, it is unclear what role it plays in chronic hypertension (HTN). Dysregulation of brain mechanisms controlling arterial pressure is strongly implicated in HTN, particularly in models involving angiotensin II (Ang II). We tested the hypothesis that ER stress in the brain is causally linked to Ang II–dependent HTN. Chronic systemic infusion of low-dose Ang II in C57BL/6 mice induced slowly developing HTN, which was abolished by co-infusion of the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) into the lateral cerebroventricle. Investigations of the brain regions involved revealed robust increases in ER stress biomarkers and profound ER morphological abnormalities in the circumventricular subfornical organ (SFO), a region outside the blood-brain barrier and replete with Ang II receptors. Ang II–induced HTN could be prevented in this model by selective genetic supplementation of the ER chaperone 78-kDa glucose-regulated protein (GRP78) in the SFO. These data demonstrate that Ang II–dependent HTN is mediated by ER stress in the brain, particularly the SFO. To our knowledge, this is the first report that ER stress, notably brain ER stress, plays a key role in chronic HTN. Taken together, these findings may have broad implications for the pathophysiology of this disease.
Colin N. Young, Xian Cao, Mallikarjuna R. Guruju, Joseph P. Pierce, Donald A. Morgan, Gang Wang, Costantino Iadecola, Allyn L. Mark, Robin L. Davisson
Progranulin (PGRN) is a widely expressed secreted protein that is linked to inflammation. In humans, PGRN haploinsufficiency is a major inherited cause of frontotemporal dementia (FTD), but how PGRN deficiency causes neurodegeneration is unknown. Here we show that loss of PGRN results in increased neuron loss in response to injury in the CNS. When exposed acutely to 1-methyl-4-(2′-methylphenyl)-1,2,3,6-tetrahydrophine (MPTP), mice lacking PGRN (Grn–/–) showed more neuron loss and increased microgliosis compared with wild-type mice. The exacerbated neuron loss was due not to selective vulnerability of Grn–/– neurons to MPTP, but rather to an increased microglial inflammatory response. Consistent with this, conditional mutants lacking PGRN in microglia exhibited MPTP-induced phenotypes similar to Grn–/– mice. Selective depletion of PGRN from microglia in mixed cortical cultures resulted in increased death of wild-type neurons in the absence of injury. Furthermore, Grn–/– microglia treated with LPS/IFN-γ exhibited an amplified inflammatory response, and conditioned media from these microglia promoted death of cultured neurons. Our results indicate that PGRN deficiency leads to dysregulated microglial activation and thereby contributes to increased neuron loss with injury. These findings suggest that PGRN deficiency may cause increased neuron loss in other forms of CNS injury accompanied by neuroinflammation.
Lauren Herl Martens, Jiasheng Zhang, Sami J. Barmada, Ping Zhou, Sherry Kamiya, Binggui Sun, Sang-Won Min, Li Gan, Steven Finkbeiner, Eric J. Huang, Robert V. Farese Jr.
Intrahepatic cholangiocarcinoma (ICC) is the second most common primary malignancy in the liver. ICC has been classified as a malignant tumor arising from cholangiocytes; however, the co-occurrence of ICC and viral hepatitis suggests that ICC originates in hepatocytes. In order to determine the cellular origin of ICC, we used a mouse model of ICC in which hepatocytes and cholangiocytes were labeled with heritable, cell type–specific reporters. Our studies reveal that ICC is generated by biliary lineage cells derived from hepatocytes, rather than cholangiocytes. Additionally, we found that Notch activation is critical for hepatocyte conversion into biliary lineage cells during the onset of ICC and its subsequent malignancy and progression. These findings will help to elucidate the pathogenic mechanism of ICC and to develop therapeutic strategies for this refractory disease.
Sayaka Sekiya, Atsushi Suzuki
Hyperprolactinemia is the most common cause of hypogonadotropic anovulation and is one of the leading causes of infertility in women aged 25–34. Hyperprolactinemia has been proposed to block ovulation through inhibition of GnRH release. Kisspeptin neurons, which express prolactin receptors, were recently identified as major regulators of GnRH neurons. To mimic the human pathology of anovulation, we continuously infused female mice with prolactin. Our studies demonstrated that hyperprolactinemia in mice induced anovulation, reduced GnRH and gonadotropin secretion, and diminished kisspeptin expression. Kisspeptin administration restored gonadotropin secretion and ovarian cyclicity, suggesting that kisspeptin neurons play a major role in hyperprolactinemic anovulation. Our studies indicate that administration of kisspeptin may serve as an alternative therapeutic approach to restore the fertility of hyperprolactinemic women who are resistant or intolerant to dopamine agonists.
Charlotte Sonigo, Justine Bouilly, Nadège Carré, Virginie Tolle, Alain Caraty, Javier Tello, Fabian-Jesus Simony-Conesa, Robert Millar, Jacques Young, Nadine Binart
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