Alagille syndrome: Chipping away at the tip of the iceberg

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy in an Israeli family

Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common monogenic form of hereditary cerebral microangiopathy, and is caused by over 170 different mutations in the NOTCH3 gene at locus 19p13.1-13.26. We report the first study of familial CADASIL in a 39-year-old Jewish woman and her mother who had died previously. The patient's investigations revealed a normal hemogram with no vascular risk factors or chronic disease. Lumbar puncture was normal. Cranial computed tomography scan revealed bilateral diffuse hypodensities in the subcortical white matter. Cranial magnetic resonance imaging showed hyperintense lesions in the cerebral white matter on T2-weighted images. On electron microscopy, a characteristic granular osmiophilic material was seen in the basement membrane surrounding the pericytes and smooth muscle cells in small-sized and medium-sized vessels. Molecular analysis of the NOTCH3 gene was performed with automatic sequencing of exon 3 and 4 (and intron-exon boundaries) showing a nucleotide c.268C > T substitution, leading to a pathogenic amino acid substitution of p.Arg90Cys, confirming a diagnosis of CADASIL. This mutation was also found in the patient's mother. Although the exact prevalence of CADASIL is not known, this disorder has been reported worldwide, and now including Jews, with a genotype and clinical phenotype similar to that in other ethnic groups.

Notch signaling through Jagged-1 is necessary to initiate chondrogenesis in human bone marrow stromal cells but must be switched off to complete chondrogenesis

We investigated Notch signaling during chondrogenesis in human bone marrow stromal cells (hMSC) in three-dimensional cell aggregate culture. Expression analysis of Notch pathway genes in 14-day chondrogenic cultures showed that the Notch ligand Jagged-1 (Jag-1) sharply increased in expression, peaking at day 2, and then declined. A Notch target gene, HEY-1, was also expressed, with a temporal profile that closely followed the expression of Jag-1, and this preceded the rise in type II collagen expression that characterized chondrogenesis. We demonstrated that the shut-down in Notch signaling was critical for full chondrogenesis, as adenoviral human Jag-1 transduction of hMSC, which caused continuous elevated expression of Jag-1 and sustained Notch signaling over 14 days, completely blocked chondrogenesis. In these cultures, there was inhibited production of extracellular matrix, and the gene expression of aggrecan and type II collagen were strongly suppressed; this may reflect the retention of a prechondrogenic state. The JAG-1-mediated Notch signaling was also shown to be necessary for chondrogenesis, as N-[N-(3,5-difluorophenacetyl-L-alanyl)]-(S)-phenylglycine t-butyl ester (DAPT) added to cultures on days 0-14 or just days 0-5 inhibited chondrogenesis, but DAPT added from day 5 did not. The results thus showed that Jag-1-mediated Notch signaling in hMSC was necessary to initiate chondrogenesis, but it must be switched off for chondrogenesis to proceed.

Cartilage, SOX9 and Notch signals in chondrogenesis

Cartilage repair is an ongoing medical challenge. Tissue engineered solutions to this problem rely on the availability of appropriately differentiated cells in sufficient numbers. This review discusses the potential of primary human articular chondrocytes and mesenchymal stem cells to fulfil this role. Chondrocytes have been transduced with a retrovirus containing the transcription factor SOX9, which permits a greatly improved response of the cells to three-dimensional culture systems, growth factor stimulation and hypoxic culture conditions. Human mesenchymal stem cells have been differentiated into chondrocytes using well-established methods, and the Notch signalling pathway has been studied in detail to establish its role during this process. Both approaches offer insights into these in vitro systems that are invaluable to understanding and designing future cartilage regeneration strategies.