Molecular Mechanisms Underlying Cochlear Degeneration in the Tubby Mouse and the Therapeutic Effect of Sulforaphane

Molecular mechanisms underlying cochlear degeneration in the tubby mouse and the therapeutic effect of sulforaphane.

Neurochem Int. 2009 Mar-Apr;54(3-4):172-9. Epub 2008 Dec 9.

Kong L, Chen GD, Zhou X, McGinnis JF, Li F, Cao W.

Department of Ophthalmology and Dean A. McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, USA.

 

As with Usher syndrome observed in humans, the two main phenotypes of the tubby mouse are progressive hearing loss and retinal degeneration. Yet, the mechanism underlying the tub-related cochlear degeneration is still unclear. The reduction/oxidation (redox) imbalance in the cell is related to many kinds of diseases. This study examined expressions of thioredoxin (Trx) and Trx reductase (TrxR), an important redox system in the cell, and the related upstream and downstream proteins of the Trx/TrxR in the tubby mouse cochlea. This report also examined the therapeutic effect of sulforaphane (SF) on the cochlear degeneration, which showed a protective effect on the tub-related retinal degeneration in our previous report. The results showed that the tub-mutation resulted in a significant suppression of Trx and TrxR expressions. Expression level of Nrf2 (NFE2 related factor 2), a transcription factor that regulates expression of Trx and TrxR and others, was also suppressed in the tubby mouse cochlea. Furthermore, a lowered level of activated extracellular signal-regulated kinase (p-ERK) was observed in the tubby mouse cochlea. In contrast, caspase-3 expression and activity were enhanced in the tubby mouse, suggesting apoptotic cell death. The tub-related molecular alterations in the cochlea were prevented by chronic treatment with sulforaphane. As a result, the sulforaphane treatment significantly delayed the tub-related cochlear degeneration. Other unknown proteins may contribute to tubby-related degeneration because Nrf2 regulates many other antioxidants besides Trx/TrxR andsulforaphane did not prevent cochlear degeneration completely although it completely prevented alterations of Nrf2 and Trx/TrxR.

 

Note from ISS:  Several crucifer sprouts including broccoli sprouts are currently the most potent natural source of sulforaphane known.  They often produce 10 to 100 times the amount of sulforaphane as their corresponding mature vegetables. ("Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens.", Proc Natl Acad Sci U S A 1997 Sep 16;94(19):10367-72.)