microRNA-181a downregulates deptor for TGFβ-induced glomerular mesangial cell hypertrophy and matrix protein...

Area of Science:

• Molecular Biology
• Cell Biology
• Nephrology

Background:

• Transforming growth factor-beta (TGFβ) is implicated in kidney diseases like diabetic nephropathy, promoting mesangial cell hypertrophy and matrix protein accumulation.
• Deptor is a key regulator of mechanistic target of rapamycin (mTOR) kinase activity, inhibiting both mTORC1 and mTORC2 complexes.
• Previous studies indicated that TGFβ inhibits deptor, leading to increased mTOR activity, but the underlying mechanism remained unclear.

Purpose of the Study:

• To elucidate the mechanism by which TGFβ regulates deptor expression in mesangial cells.
• To investigate the role of microRNA-181a (miR-181a) in mediating TGFβ-induced changes in deptor and mTOR signaling.
• To determine the contribution of the miR-181a/deptor/mTOR pathway to mesangial cell hypertrophy and fibronectin production.

Main Methods:

• Mesangial cells were treated with TGFβ to assess changes in miR-181a and deptor expression.
• miR-181a mimics and inhibitors were used to manipulate miR-181a levels and observe effects on deptor, mTOR activity, and downstream targets.
• Western blotting and phosphorylation assays were employed to evaluate protein levels and activation states of key signaling molecules, including Akt, PRAS40, tuberin, 4EBP-1, and eEF2 kinase.
• Cellular hypertrophy and fibronectin expression were quantified.

Main Results:

• TGFβ stimulation led to increased miR-181a expression in mesangial cells, subsequently downregulating deptor.
• Downregulation of deptor by miR-181a augmented mTORC2 activity, activating Akt kinase, which in turn promoted mTORC1 activation.
• miR-181a mimicry enhanced mTORC1 and mTORC2 activities, increasing phosphorylation of 4EBP-1 and eEF2 kinase, leading to elevated protein synthesis, mesangial cell hypertrophy, and fibronectin expression.
• Inhibition of miR-181a reversed these effects in a deptor-dependent manner.

Conclusions:

• This study identifies miR-181a as a direct regulator of deptor expression in mesangial cells.
• The TGFβ-miR-181a-deptor axis represents a novel pathway contributing to mesangial cell hypertrophy and matrix protein accumulation in kidney disease.
• Targeting the miR-181a/deptor pathway may offer a therapeutic strategy for renal complications associated with TGFβ signaling.