Topical Area: Dietary Bioactive Components
Epithelial to mesenchymal transition (EMT) is a process by which epithelial cells acquire mesenchymal properties. This process contributes to the accumulation of matrix proteins in kidney and leads to renal glomeruli fibrosis. Tangeretin is an O-polymethoxylated flavone with anti-inflammatory and antioxidant properties that is found in citrus peels. This study investigated the renoprotective effects of tangeretin on EMT-mediated podocyte injury and fibrosis caused by hyperglycemia.
Mouse glomerular epithelial cells (podocyte) were incubated in media containing 5.5 mM glucose, 27.5 mM mannitol as an osmotic control or 33 mM glucose (high glucose) in the absence and presence of 1-20 μM tangeretin for up to 4 days. Antibodies of E-cadherin, N-cadherin, α-SMA, nephrin, podocin, P-cadherin and collagen1 were used for Western blotting. The in vivo animal model employed db/db mice orally administrated with 10 mg/kg tangeretin for 8 weeks. Kidney tissue extracts of were Western-blotted, and tissue sections cut down in 5 µM thickness were immunohistochemically stained. In addition, kidney tissue sections (ultrathin sections, 70 nm) were observed with transmission electron microscopy (TEM).
Results : Non-toxic tangeretin enhanced expression of the podocyte slit diaphragm proteins of nephrin, podocin and P-cadherin down-regulated by glucose stimulation. Also, tangeretin inhibited high glucose-induced expression of the mesenchymal markers of N-cadherin and α-smooth muscle actin, whereas the induction of the epithelial marker E-cadherin was enhanced. Furthermore tangeretin attenuated the fibronectin induction and collagen production elevated by the presence of high glucose. The TEM images revealed that podocyte foot process effacement occurred in diabetic mouse glomeruli. However, oral administration of 10 mg/kg tangeretin reduced urine albumin excretion and improved foot process effacement of diabetic podocytes through inhibiting loss of glomerular slit junction proteins.
These results demonstrated that tangeretin maintained the structures of podocyte slit diaphragm in a robust form, and inhibited podocyte injury through blocking epithelial to mesenchymal transition of podocytes. Therefore, tangeretin may be a potent renoprotective agent counteracting diabetes-associated loss of podocyte slit diaphragm and maintaining glomerular filtration barrier.
Funding Sources : This work was supported by the National Research Foundation of Korea (NRF) grants funded by the
Korea government (MEST) ( NRF-2017R1A6A3A04011473).