SUMMARY Hepatic glucose release into the circulation is vital for brain function and survival during periods of fasting and is modulated by an array of hormones that precisely regulate plasma glucose levels. We have identified a fasting-induced protein hormone that modulates hepatic glucose release. It is the C-terminal cleavage product of profibrillin, and we name it Asprosin. Asprosin is secreted by white adipose, circulates at nanomolar levels, and is recruited to the liver, where it activates the G protein-cAMP-PKA pathway, resulting in rapid glucose release into the circulation. Humans and mice with insulin resistance show pathologically elevated plasma asprosin, and its loss of function via immunologic or genetic means has a profound glucose- and insulin-lowering effect secondary to reduced hepatic glucose release. Asprosin represents a glucogenic protein hormone, and therapeutically targeting it may be beneficial in type II diabetes and metabolic syndrome.

A full understanding of the microenvironmental factors that control the activities of skeletal stem cells (also known as mesenchymal stem cells [MSCs]) in the adult bone marrow holds great promise for developing new therapeutic strategies to mitigate age-related diseases of bone and cartilage degeneration. Bone loss is an understudied manifestation of Marfan syndrome, a multisystem disease associated with mutations in the extracellular matrix protein and TGFb modulator fibrillin-1. Here we demonstrate that progressive loss of cancellous bone in mice with limbs deficient for fibrillin-1 (Fbn1 Prx1-/-mice) is accounted for by premature depletion of MSCs and osteoprogenitor cells combined with constitutively enhanced bone resorption. Longitudinal analyses of Fbn1 Prx1-/-mice showed incremental bone loss and trabecular microarchitecture degeneration accompanied by a progressive decrease in the number and clonogenic potential of MSCs. Significant paucity of marrow fat cells in the long bones of Fbn1 Prx1-/-mice, together with reduced adipogenic potential of marrow stromal cell cultures, indicated an additional defect in MSC differentiation. This postulate was corroborated by showing that an Fbn1-silenced osteoprogenitor cell line cultured in the presence of insulin yielded fewer than normal adipocytes and exhibited relatively lower PPARg levels. Consonant with fibrillin-1 modulation of TGFb bioavailability, cultures of marrow stromal cells from Fbn1 Prx1-/-limb bones showed improper overactivation of latent TGFb. In line with this finding, systemic TGFb neutralization improved bone mass and trabecular microarchitecture along with normalizing the number of MSCs, osteoprogenitor cells, and marrow adipocytes. Collectively, our findings show that fibrillin-1 regulates MSC activity by modulating TGFb bioavailability within the microenvironment of marrow niches.

Loss-of-function experiments in mice have yielded invaluable mechanistic insights into the pathogenesis of Marfan syndrome (MFS) and implicitly, into the multiple roles fibrillin-1 microfibrils play in the developing and adult organism. Unfortunately, neonatal death from aortic complications of mice lacking fibrillin-1 (Fbn1−/− mice) has limited the scope of these studies. Here we report the creation of a conditional mutant allele (Fbn1fneo) that contains loxP sites bordering exon1 of Fbn1 and an frt-flanked neo expression cassette downstream of it. Fbn1fneo/+ mice were crossed with FLPeR mice and the resulting Fbn1Lox/+ progeny were crossed with Fbn1−;CMV-Cre mice to generate Fbn1CMV−/− mice, which were found to phenocopy the vascular abnormalities of Fbn1−/− mice. Furthermore, mating Fbn1Lox/+ mice with Prx1-Cre or Osx-Cre mice revealed an unappreciated role of fibrillin-1 microfibrils in restricting osteoprogenitor cell recruitment. Fbn1Lox/+ mice are therefore an informative genetic resource to further dissect MFS pathogenesis and the role of extracellular fibrillin-1 assemblies in organ development and homeostasis.

Synthesis of a novel, stable reagent (1,3-benzothiazol-2-ylsulfonyl)fluoroacetonitrile from readily available ethyl α-(1,3-benzothiazol-2-ylsulfanyl)-α-fluoroacetate is reported. Aldehydes undergo condensations with (1,3-benzothiazol-2-ylsulfonyl)fluoroacetonitrile in the presence of DBU leading to α-fluoro acrylonitriles in high yields and with good Z-stereoselectivity. Lowering of reaction temperature increases the Z selectivity.

We have recently demonstrated that fibrillin-1 assemblies regulate the fate of skeletal stem cells (aka, mesenchymal stem cells [MSCs]) by modulating TGFβ activity within the microenvironment of adult bone marrow niches. Since MSCs can also influence hematopoietic stem cell (HSC) activities, here we investigated adult hematopoiesis in mice with Cre-mediated inactivation of the fibrillin-1 (Fbn1) gene in the mesenchyme of the forming limbs (Fbn1Prx1−/− mice). Analyses of 3-month-old Fbn1Prx1−/− mice revealed a statistically significant increase of circulating red blood cells, which a differentiation assay correlated with augmented erythropoiesis. This finding, together with evidence of fibrillin-1 deposition in erythroblastic niches, supported the notion that this extracellular matrix protein normally restricts differentiation of erythroid progenitors. Whereas flow cytometry measurements identified a decreased HSC frequency in mutant relative to wild type mice, no appreciable differences were noted with regard to the relative abundance and differentiation potential of myeloid progenitor cells. Together these findings implied that fibrillin-1 normally promotes HSC expansion but does not influence cell lineage commitment. Since local TGFβ hyperactivity has been associated with abnormal osteogenesis in Fbn1Prx1−/− mice, 1-month-old mutant and wild type animals were systemically treated for 8 weeks with either a pan-TGF-β-neutralizing antibody or an antibody of the same IgG1 isotype. The distinct outcomes of these pharmacological interventions strongly suggest that fibrillin-1 differentially modulates TGFβ activity in HSC vs. erythroid niches.

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Nitriles P 0350Fluoro-Julia Olefination as a Mild, High-Yielding Route to α-Fluoro Acrylonitriles. -The (Z) isomers are predominantly formed. -(DEL SOLAR, M.; GHOSH, A. K.; ZAJC*, B.; J. Org. Chem. 73 (2008) 21, 8206-8211; Dep. Chem., City Coll., City Univ., New York, NY 10031, USA; Eng.) -Jannicke 11-064

IntroductionDissecting TAA in MFS is associated with elevated TGFβ activity secondary to structural or quantitative defects in FBN1. Perinatal lethality of mice with germ line inactivation of Fbn1 has underscored the importance of fibrillin microfibrils in aortic growth and homeostasis without identifying the main tissue compartment contributing to TAA.ObjectiveDetermine the contribution of fibrillin‐1 production by VSMCs and ECs in MFS vascular pathology.MethodA new conditional Fbn1 mouse model was created to allow for the selective study of fibrillin‐1 in unique tissues. Female mice with the conditional allele (Fbn1fl) were crossed with male transgenic mice harboring a germ line null allele (Fbn1mgN) and expressing Cre in either VSMCs (SM22α‐Cre) or ECs (Cdh5‐Cre). The germ line null allele was paired with the conditional allele to increase the probability of tissue specific Cre excision. Tissue specific Cre excision was monitored by crossing the tissue specific mice with RosaLacZ reporter mice.ResultsInactivation of fibrillin‐1 in VSMCs (Fbn1fl/mgN; SM22α‐Cre+), but not ECs, replicates the germ line null phenotype with elastic fiber fragmentation, aortic aneurysm, and death due to dissection by P16.ConclusionsLack of fibrillin‐1 production by VSMCs in the media of the ascending aorta is necessary and sufficient for the development of TAA.