ABSTRACT
The Smads are a group of related intracellular proteins critical for transmitting the signals to the nucleus from the transforming growth factor-beta superfamily at the cell surface. Knockout of the Smad5 is embryonic lethal. However, the Smad5 knockout of single allele (+/-) could survive. We used Smad5 heterozygous knockout (+/-) to determine the role of Smad5 in the development of inner ear morphology and function. In situ hybridization showed that Smad5 was expressed predominantly in hair cells, spiral ganglion, and supporting cells. Measurements of hearing thresholds using auditory brainstem response showed that Smad5 defect resulted in progressive hearing loss between 4 and 24 weeks after birth. Morphological examination revealed apoptosis in the inner ear, with significant loss of outer hair cells in adult Smad5 mutant mice. Our results indicated that deficiency in the Smad5-mediated signaling resulted in apoptosis of hair cells, suggesting Smad5 is a gene that may be related with presbycusis.
Subject(s)
Apoptosis/genetics , Cochlea/pathology , Hair Cells, Auditory/pathology , Hearing Loss/genetics , Smad5 Protein/deficiency , Smad5 Protein/metabolism , Acoustic Stimulation/methods , Age Factors , Animals , Animals, Newborn , Auditory Threshold/physiology , Cochlea/growth & development , Cochlea/ultrastructure , Hair Cells, Auditory/ultrastructure , In Situ Nick-End Labeling/methods , Mice , Mice, Knockout , Microscopy, Electron/methodsABSTRACT
SMAD3 is one of the receptor-activated SMADs which are important in TGF-beta signal transduction. Smad3-null mice show accelerated cutaneous wound healing compared with wild-type mice. In this work, we investigated the functions and the mechanism of Smad3-mediated TGF-beta signal on matrix metaloproteinase-2 (MMP-2) in mouse fibroblast. We found that MMP-2 at wound bed was expressed earlier in Smad3-null mice than that in wild type and heterozygotes. In the sera of wounding mice, the activity of MMP-2 was also remarkably higher in Smad3-null mice than that in the other two. The embryonic fibroblasts were separated from Smad3 knockout mice to test the function of Smad3 in modulating the expression of MMP-2. The results showed that the expression and activity of MMP-2 in Smad3-null fibroblasts were higher than those in wild type cells. TGF-beta1 could increase the MMP-2 activities in both Smad3 mutant and wild type fibroblasts. The expression and activity of MMP-2 were inhibited by over expression of SMAD3 in Smad3-null fibroblasts, while the expression and activity of MMP-2 were increased by over expression of anti-sense Smad3 in wild type cells. All these results showed that SMAD3 inhibited the expression of MMP-2 in mouse embryonic fibroblasts.
