Alport syndrome is a genetic disorder resulting from mutations in type IV collagen genes. The defect results in pathological changes in kidney glomerular and inner-ear basement membranes. In the kidney, progressive glomerulonephritis culminates in tubulointerstitial fibrosis and death. Using gene knockout-mouse models, we demonstrate that two different pathways, one mediated by transforming growth factor (TGF)-beta1 and the other by integrin alpha1beta1, affect Alport glomerular pathogenesis in distinct ways. In Alport mice that are also null for integrin alpha1 expression, expansion of the mesangial matrix and podocyte foot process effacement are attenuated. The novel observation of nonnative laminin isoforms (laminin-2 and/or laminin-4) accumulating in the glomerular basement membrane of Alport mice is markedly reduced in the double knockouts. The second pathway, mediated by TGF-beta1, was blocked using a soluble fusion protein comprising the extracellular domain of the TGF-beta1 type II receptor. This inhibitor prevents focal thickening of the glomerular basement membrane, but does not prevent effacement of the podocyte foot processes. If both integrin alpha1beta1 and TGF-beta1 pathways are functionally inhibited, glomerular foot process and glomerular basement membrane morphology are primarily restored and renal function is markedly improved. These data suggest that integrin alpha1beta1 and TGF-beta1 may provide useful targets for a dual therapy aimed at slowing disease progression in Alport glomerulonephritis.
Perlecan knock-in mice were developed to model Schwartz-Jampel syndrome (SJS), a skeletal disease resulting from decreased perlecan. Two mouse strains were generated: those carrying a C-to-Y mutation at residue 1532 and the neomycin cassette (C1532Yneo) and those harboring the mutation alone (C1532Y). Immunostaining, biochemistry, size measurements, skeletal studies and histology revealed Hspg2 transcriptional changes in C1532Yneo mice, leading to reduced perlecan secretion and a skeletal disease phenotype characteristic of SJS patients. Skeletal disease features include smaller size, impaired mineralization, misshapen bones, flat face and joint dysplasias reminiscent of osteoarthritis and osteonecrosis. Moreover, C1532Yneo mice displayed transient expansion of hypertrophic cartilage in the growth plate concomitant with radial trabecular bone orientation. In contrast, C1532Y mice, harboring only the mutation associated with SJS, displayed a mild phenotype, inconsistent with SJS. These studies question the C1532Y mutation as the sole causative factor of SJS in the human family harboring this alteration and imply that transcriptional changes leading to perlecan reduction may represent the disease mechanism for SJS.
This review summarizes our current understanding of the presence and function of heparan sulfate proteoglycans (HSPGs) in skeletal development and hematopoiesis. Although proteoglycans (PGs) comprise a large and diverse group of cell surface and matrix molecules, we chose to focus on HSPGs owing to their many proposed functions in skeletogenesis and hematopoiesis. Specifically, we discuss how HSPGs play predominant roles in establishing and regulating niches during skeleto-hematopoietic development by participating in distinct developmental processes such as patterning, compartmentalization, growth, differentiation, and maintenance of tissues. Special emphasis is placed on our novel hypothesis that mechanistically links endochondral skeletogenesis to the establishment of the hematopoietic stem cell (HSC) niche in the marrow. HSPGs may contribute to these developmental processes through their unique abilities to establish and mediate morphogen, growth factor, and cytokine gradients; facilitate signaling; provide structural stability to tissues; and act as molecular filters and barriers. Developmental TRIBUTE TO DR. ELIZABETH D. HAYDr. Elizabeth Dexter Hay, "Betty" to her friends, would often introduce her seminars on extracellular matrix (ECM) and epithelial-mesenchymal cell transformations by showing pictures of her cats asleep intertwined with a blanket. She would use this analogy to highlight the intimate association that exists between a cell and its ECM during development. She was a pioneer who brought forth the notion that the ECM is not just a static "stuffing between cells," but has interactive and instructive roles in development.Betty's contribution to the ECM field began with her seminal discoveries in the emerging field of electron microscopy. She worked with Keith Porter, George Palade, Don Fawcett, Susumo Ito, Jean-Paul Revel, and others to unravel the intricate microanatomy of the cell and its ECM. Once, when working with Jean-Paul Revel to extend autoradiography to the ultrastructural level, Betty noticed that tritiated proline was incorporated into collagen in the ECM outside of the cartilage cells. Betty went on to demonstrate that epithelial cells, as well as other non-fibroblastic cells, do secrete collagen. Moreover, in her descriptions of the development and structure of the various matrices, Betty brought forth the hypothesis that the ECM interacts with cells, and that through these interactions, the cells are instructed to modify their behavior. This notion was showcased in the "Epithelial-Mesenchymal Transformation Model" she proposed to describe the dramatic morphological transformations of epithelial cells suspended in collagen gels.Among her numerous scientific accomplishments, Betty can be considered a founder of the field of cell biology. Moreover, through her personal attributes and interactions with col- leagues and her protegees, Betty has set the standard for many a scientist. This review is a tribute to Betty, a friend, colleague, and mentor, and highlights our developing premi...
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