Bi-allelic JAM2 Variants Lead to Early-Onset Recessive Primary Familial Brain Calcification.

Primary familial brain calcification (PFBC) is a rare neurodegenerative disorder characterized by a combination of neurological, psychiatric, and cognitive decline associated with calcium deposition on brain imaging. To date, mutations in five genes have been linked to PFBC. However, more than 50% of individuals affected by PFBC have no molecular diagnosis. We report four unrelated families presenting with initial learning difficulties and seizures and later psychiatric symptoms, cerebellar ataxia, extrapyramidal signs, and extensive calcifications on brain imaging. Through a combination of homozygosity mapping and exome sequencing, we mapped this phenotype to chromosome 21q21.3 and identified bi-allelic variants in JAM2. JAM2 encodes for the junctional-adhesion-molecule-2, a key tight-junction protein in blood-brain-barrier permeability. We show that JAM2 variants lead to reduction of JAM2 mRNA expression and absence of JAM2 protein in patient's fibroblasts, consistent with a loss-of-function mechanism. We show that the human phenotype is replicated in the jam2 complete knockout mouse (jam2 KO). Furthermore, neuropathology of jam2 KO mouse showed prominent vacuolation in the cerebral cortex, thalamus, and cerebellum and particularly widespread vacuolation in the midbrain with reactive astrogliosis and neuronal density reduction. The regions of the human brain affected on neuroimaging are similar to the affected brain areas in the myorg PFBC null mouse. Along with JAM3 and OCLN, JAM2 is the third tight-junction gene in which bi-allelic variants are associated with brain calcification, suggesting that defective cell-to-cell adhesion and dysfunction of the movement of solutes through the paracellular spaces in the neurovascular unit is a key mechanism in CNS calcification

Targeting Vascular NADPH Oxidase 1 Blocks Tumor Angiogenesis through a PPARα Mediated Mechanism

Reactive oxygen species, ROS, are regulators of endothelial cell migration, proliferation and survival, events critically involved in angiogenesis. Different isoforms of ROS-generating NOX enzymes are expressed in the vasculature and provide distinct signaling cues through differential localization and activation. We show that mice deficient in NOX1, but not NOX2 or NOX4, have impaired angiogenesis. NOX1 expression and activity is increased in primary mouse and human endothelial cells upon angiogenic stimulation. NOX1 silencing decreases endothelial cell migration and tube-like structure formation, through the inhibition of PPARα, a regulator of NF-κB. Administration of a novel NOX-specific inhibitor reduced angiogenesis and tumor growth in vivo in a PPARα dependent manner. In conclusion, vascular NOX1 is a critical mediator of angiogenesis and an attractive target for anti-angiogenic therapies

Antibody against junctional adhesion molecule-C inhibits angiogenesis and tumor growth

The junctional adhesion molecule-C (JAM-C) was recently described as an adhesion molecule localized at interendothelial contacts and involved in leukocyte transendothelial migration. The protein JAM-C interacts with polarity complex molecules and regulates the activity of the small GTPase Cdc42. The angiogenesis process involves rearrangement of endothelial junctions and implicates modulation of cell polarity. We tested whether JAM-C plays a role in angiogenesis using tumor grafts and hypoxia-induced retinal neovascularization. Treatment with a monoclonal antibody directed against JAM-C reduces tumor growth and infiltration of macrophages into tumors. The antibody decreases angiogenesis in the model of hypoxia-induced retinal neovascularization in vivo and vessel outgrowth from aortic rings in vitro. Importantly, the antibody does not induce pathologic side effects in vivo. These findings show for the first time a role for JAM-C in angiogenesis and define JAM-C as a valuable target for antitumor therapies

Spermatid differentiation requires the assembly of a cell polarity complex downstream of junctional adhesion molecule-C

During spermatogenesis in the mammalian testis, stem cells (spermatogonia) differentiate into spermatocytes, which subsequently undergo two consecutive meiotic divisions to give rise to haploid spermatids. These cells are initially round but progressively elongate, condense their nuclei, acquire flagellar and acrosomal structures, and shed a significant amount of their cytoplasm to form spermatozoa (the sperm cells) in a developmental cascade termed spermiogenesis. Defects in these processes will lead to a lack of mature sperm cells (azoospermia), which is a major cause of male infertility in the human population. Here we report that a cell-surface protein of the immunoglobulin superfamily, junctional adhesion molecule-C (JAM-C), is critically required for the differentiation of round spermatids into spermatozoa in mice. We found that Jam-C is essential for the polarization of round spermatids, a function that we attribute to its role in the assembly of a cell polarity complex

Poly(ADP-ribose) polymerase-1 (PARP-1) controls lung cell proliferation and repair after hyperoxia-induced lung damage

Oxygen-based therapies expose lung to elevated levels of ROS and induce lung cell damage and inflammation. Injured cells are replaced through increased proliferation and differentiation of epithelial cells and fibroblasts. Failure to modulate these processes leads to excessive cell proliferation, collagen deposition, fibrosis, and chronic lung disease. Poly(ADP-ribose) polymerase-1 (PARP-1) is activated in response to DNA damage and participates in DNA repair, genomic integrity, and cell death. In this study, we evaluated the role of PARP-1 in lung repair during recovery after acute hyperoxia exposure. We exposed PARP-1 -/- and wild-type mice for 64 h to 100% hyperoxia and let them recover in air for 5-21 days. PARP-1-deficient mice exhibited significantly higher lung cell hyperplasia and proliferation than PARP-1 +/+ animals after 5 and 10 days of recovery. This was accompanied by an increased inflammatory response in PARP-1 -/- compared with wild-type animals, characterized by neutrophil infiltration and increased IL-6 levels in bronchoalveolar lavages. These lesions were reversible, since the extent of the hyperplastic regions was reduced after 21 days of recovery and did not result in fibrosis. In vitro, lung primary fibroblasts derived from PARP-1 -/- mice showed a higher proliferative response than PARP-1 +/+ cells during air recovery after hyperoxia-induced growth arrest. Altogether, these results reveal an essential role of PARP-1 in the control of cell repair and tissue remodeling after hyperoxia-induced lung injury

Altered cellular proliferation and mesoderm patterning in Polycomb-M33-deficient mice

International audienceIn Drosophila, the trithorax-group and the Polycomb-group genes are necessary to maintain the expression of the homeobox genes in the appropriate segments. Loss-of-function mutations in those groups of genes lead to misexpression of the homeotic genes resulting in segmental homeotic transformations. Recently, mouse homologues of the Polycomb-group genes were identified including M33, the murine counterpart of Polycomb. In this report, M33 was targeted in mice by homologous recombination in embryonic stem (ES) cells to assess its function during development. Homozygous M33 (−/−) mice show greatly retarded growth, homeotic transformations of the axial skeleton, sternal and limb malformations and a failure to expand in vitro of several cell types including lymphocytes and fibroblasts. In addition, M33 null mutant mice show an aggravation of the skeletal malformations when treated to RA at embryonic day 7.5, leading to the hypothesis that, during development, the M33 gene might play a role in defining access to retinoic acid response elements localised in the regulatory regions of several Hox genes

Altered cellular proliferation and mesoderm patterning in Polycomb-M33-deficient mice

International audienceIn Drosophila, the trithorax-group and the Polycomb-group genes are necessary to maintain the expression of the homeobox genes in the appropriate segments. Loss-of-function mutations in those groups of genes lead to misexpression of the homeotic genes resulting in segmental homeotic transformations. Recently, mouse homologues of the Polycomb-group genes were identified including M33, the murine counterpart of Polycomb. In this report, M33 was targeted in mice by homologous recombination in embryonic stem (ES) cells to assess its function during development. Homozygous M33 (−/−) mice show greatly retarded growth, homeotic transformations of the axial skeleton, sternal and limb malformations and a failure to expand in vitro of several cell types including lymphocytes and fibroblasts. In addition, M33 null mutant mice show an aggravation of the skeletal malformations when treated to RA at embryonic day 7.5, leading to the hypothesis that, during development, the M33 gene might play a role in defining access to retinoic acid response elements localised in the regulatory regions of several Hox genes

Junctional adhesion molecule C (JAM-C) distinguishes CD27+ germinal center B lymphocytes from non-germinal center cells and constitutes a new diagnostic tool for B-cell malignancies

Differentiation of naive B cells into plasma cells or memory cells occurs in the germinal centers (GCs) of lymph follicles or alternatively via a GC- and T-cell-independent pathway. It is currently assumed that B-cell lymphomas correlate to normal B-cell differentiation stages, but the precise correlation of several B-cell lymphomas to these two pathways remains controversial. In the present report, we describe the junctional adhesion molecule C (JAM-C), currently identified at the cell-cell border of endothelial cells, as a new B-cell marker with a tightly regulated expression during B-cell differentiation. Expression of JAM-C in tonsils allows distinction between two CD27+ B-cell subpopulations: JAM-C- GC B cells and JAM-C+ non-germinal B cells. The expression of JAM-C in different B-cell lymphomas reveals a disease-specific pattern and allows a clear distinction between JAM-C- lymphoproliferative syndromes (chronic lymphocytic leukemia, mantle cell lymphoma and follicular lymphoma) and JAM-C+ ones (hairy cell leukemia, marginal zone B-cell lymphoma). Therefore, we propose JAM-C as a new identification tool in B-cell lymphoma diagnosis

JAM-C Induces endothelial cell permeability through its association and regulation of beta(3) integrins

Objectives: The molecular mechanisms regulating vascular permeability are only now being elucidated. The junctional adhesion molecule (JAM) JAM-C has been linked to the induction of vascular permeability. We sought to understand the mechanism whereby JAM-C may disrupt junctional integrity in endothelial cells (ECs). Methods and Results: We show here that JAM-C alters permeability through modulation of integrin activity. JAM-C overexpression results in an increase in JAM-C at junctions and an increase in permeability. Conversely, knockdown of JAM-C by siRNA results in a reduction in permeability. JAM-C associates with vβ3 integrin and regulates its localization and activity. JAM-C also inhibits the activation state of the β1 integrin although it does not associate with this integrin. These changes induced on the integrins are mediated through regulation of the small GTPase, Rap1b but not Rap1a. Thrombin, a powerful inductor of vascular leak, causes localization of JAM-C into the junctions, whereas angiopoietin-1, an inhibitor of permeability, prevents JAM-C translocation. Conclusions: The regulation of EC junctional integrity involves the coordinated and dynamic modification of localization and activity of junctional stabilizers such as the integrin β3 and the destabilizer, JAM-C.Xiaochun Li, Milena Stankovic, Boris P.-L. Lee, Michel Aurrand-Lions, Chris N. Hahn, Ying Lu, Beat A. Imhof, Mathew A. Vadas and Jennifer R. Gamble