The laminins in the murine inner ear: developmental transitions and expression in cochlear basement membranes.

The laminins are a family of heterotrimeric extracellular matrix molecules that form suprastructural networks in basement membranes and elsewhere. They interact with integrin receptors, playing key roles in modulating programs of cytodifferentiation and maintaining tissue homeostasis in animals. Earlier studies have demonstrated an extensive laminin network in both the developing and adult cochlea, primarily associated with the basement membranes. These studies, however, did not address the laminin chain composition of these networks. In this study, we used antibodies specific for the known laminin chains to examine the composition of laminins in both the developing and adult murine cochlea. The results illustrate a complex and dynamic postnatal developmental regulation pattern for most of these chains, and suggest that an unusually large number of laminin heterotrimers are present in both the developing and adult cochlea. The laminin composition at postnatal day 2 is relatively simple. By postnatal day 7, however, activation of several laminin chains results in a very complex laminin composition. In the basement membrane underlying the region of the basilar membrane under the developing organ of Corti, eight of the 11 known basement membrane laminins are possible by co-localization inference. Dynamic changes in expression continue through day 14, but simplify by adulthood. Thus, the most dynamic period for laminin expression in the mouse cochlea coincides with terminal cytodifferentiation of the cochlear epithelial structures. Considering the well established role of laminins in regulating both embryonic and organ development in other systems, these data suggest a closer look at the role of the laminins in cochlear development and function may be warranted.

Role for transforming growth factor-beta1 in alport renal disease progression.

BACKGROUND: Alport syndrome results from mutations in either the alpha3(IV), alpha4(IV), or alpha5(IV) collagen genes. The disease is characterized by a progressive glomerulonephritis usually associated with a high-frequency sensorineural hearing loss. A mouse model for an autosomal form of Alport syndrome [collagen alpha3(IV) knockout] was produced and characterized. In this study, the model was exploited to demonstrate a potential role for transforming growth factor-beta1 (TGF-beta1) in Alport renal disease pathogenesis. METHODS: Kidneys from normal and Alport mice, taken at different stages during the course of renal disease progression, were analyzed by Northern blot, in situ hybridization, and immunohistology for expression of TGF-beta1 and components of the extracellular matrix. Normal and Alport human kidney was examined for TGF-beta1 expression using RNase protection. RESULTS: The mRNAs encoding TGF-beta1 (in both mouse and human), entactin, fibronectin, and the collagen alpha1(IV) and alpha2(IV) chains were significantly induced in total kidney as a function of Alport renal disease progression. The induction of these specific mRNAs was observed in the glomerular podocytes of animals with advanced disease. Type IV collagen, laminin-1, and fibronectin were markedly elevated in the tubulointerstitium at 10 weeks, but not at 6 weeks, suggesting that elevated expression of specific mRNAs on Northern blots reflects events associated with tubulointerstitial fibrosis. CONCLUSIONS: The concomitant accumulation of mRNAs encoding TGF-beta1 and extracellular matrix components in the podocytes of diseased kidneys may reflect key events in Alport renal disease progression. These data suggest a role for TGF-beta1 in both glomerular and tubulointerstitial damage associated with Alport syndrome.

Expression of the major basement membrane-associated proteins during postnatal development in the murine cochlea.

The major basement membrane-associated proteins, including laminin-1, fibronectin, heparan sulfate proteoglycan (HSP), and entactin, were examined by immunofluorescence microscopy during postnatal development of the mouse cochlea. Samples were collected every 2 days through 8 days, and again at 14 days after birth. In the neonate, staining for HSP entactin and laminin-1 was barely visible; however, antibodies against fibronectin displayed intense immunoreactivity in nearly every cochlear tissue. Fibronectin is progressively inactivated in all tissues except the basilar membrane where it persists at high levels to adulthood. Laminin-1, entactin, and HSP illustrate remarkable temporal and spatial coordinate regulation. Elevated expression of these proteins is observed at 2 postnatal days (PND), and persists in the membranes surrounding the spiral ganglion cell bodies. Transient expression of laminin-1 and entactin, an to a lesser extent HSP, is observed from PND4 to PND8 in a track of membrane running from the interdental cells of the spiral limbus down the inner sulcus, across the basilar membrane, up the external sulcus to the spiral prominence, and branching into the spiral ligament ensheathing the root cell processes. By PND14 the abundance of these proteins is greatly reduced along this track. The abundance and dynamic regulation of these major basement membrane-associated proteins suggests that they play an important role in postnatal cochlear development.