Purification of Endogenous Drosophila Transient Receptor Potential Channels.

Drosophila phototransduction is one of the fastest known G protein-coupled signaling pathways. To ensure the specificity and efficiency of this cascade, the calcium (Ca2+)-permeable cation channel, transient receptor potential (TRP), binds tightly to the scaffold protein, inactivation-no-after-potential D (INAD), and forms a large signaling protein complex with eye-specific protein kinase C (ePKC) and phospholipase Cß/No receptor potential A (PLCß/NORPA). However, the biochemical properties of the Drosophila TRP channel remain unclear. Based on the assembling mechanism of INAD protein complex, a modified affinity purification plus competition strategy was developed to purify the endogenous TRP channel. First, the purified histidine (His)-tagged NORPA 863-1095 fragment was bound to Ni-beads and used as bait to pull down the endogenous INAD protein complex from Drosophila head homogenates. Then, excessive purified glutathione S-transferase (GST)-tagged TRP 1261-1275 fragment was added to the Ni-beads to compete with the TRP channel. Finally, the TRP channel in the supernatant was separated from the excessive TRP 1261-1275 peptide by size-exclusion chromatography. This method makes it possible to study the gating mechanism of the Drosophila TRP channel from both biochemical and structural angles. The electrophysiology properties of purified Drosophila TRP channels can also be measured in the future.

Pentoxifylline inhibits transforming growth factor-beta signaling and renal fibrosis in experimental crescentic glomerulonephritis in rats.

BACKGROUND/AIMS: Pentoxifylline (PTX) has been shown to inhibit renal inflammation in a rat model of crescentic glomerulonephritis. The present study investigated the role of PTX in renal fibrosis in rats with crescentic glomerulonephritis. METHODS: A rat model of accelerated anti-glomerular basement membrane glomerulonephritis was induced and treated with PTX or vehicle control for 3, 7, 14 and 28 days. The therapeutic effect and mechanism of PTX on renal fibrosis were examined by Northern blot and immunohistochemistry. RESULTS: Diseased rats treated with vehicle control developed a severe crescentic glomerulonephritis with progressive renal fibrosis identified by a marked accumulation of alpha-SMA+ myofibroblasts and collagen matrix. This was associated with tubular epithelial-myofibroblast transition as evident by de novo expression of alpha-SMA and a loss of E-cadherin on damaged tubular epithelial cells. Further studies revealed that severe renal fibrosis was associated with upregulation of renal TGF-beta1 and activation of TGF-beta/Smad signaling, which was blocked by treatment with PTX. CONCLUSIONS: PTX may be an anti-fibrosis agent capable of inhibiting renal fibrosis in a rat model of crescentic glomerulonephritis. Blockade of TGF-beta1 expression and Smad2/3 activation may be a mechanism by which PTX inhibits renal fibrosis.