Tubular Semaphorin3B Mediates Glomerular Parietal Epithelial Cell Activity
Abstract
Introduction:
A recent experimental study by our lab indicated that isolated, clinically recovered, proximal tubule damage may sensitize the glomerulus to subsequent injury - independent of proinflammatory and profibrotic cytokine activation. These findings suggest previously unidentified direct/paracrine ligand- receptor interactions at the glomerulotubular junction. Preliminary spatial transcriptomics data revealed a concomitant decrease in tubular SEMA3B ligand and glomerular NRP1 / PLXNA2 receptor expression following proximal tubule injury. We therefore hypothesize that downregulation of this specific ligand/receptor complex plays a potential role in glomerular parietal epithelial cell activation, whereby the decrease of this ligand/receptor pair promotes injury.
Methods:
Evaluate proximal tubule epithelial cells (PTEC) SEMA3B expression and glomerular parietal epithelial cells (PEC) NRP1/PLXNA2 expression after tubular injury in vivo. Then, perform an indirect co-culture to isolate and examine PTEC-PEC mediated SEMA3B activity - independent of potential environmental interference.
Results:
Paraffin-embedded kidney tissue samples from control (DT- LMB2+ ) and prior acute tubular injury (DT+ LMB2+) mice were visualized (IHC) with recombinant SEMA3B / NRP1 / PLXNA2 primary antibodies. After injury, PTEC SEMA3B ligand expression decreased in the proximal tubule but increased in the distal tubule, with insignificant urinary SEMA3B concentration change. PEC localization of NRP1 shifts from the cytoplasm to outer membrane following tubular injury. In vitro, AA exposed PTC supernatant contained markedly reduced levels of SEMA3B protein. The PECs exposed to the injured PTC supernatant showed increased NRP1 but not PLXNA2 expression.
Conclusion:
The concomitant decrease in SEMA3B / NRP1 / PlXNA2 expression following tubular injury in vitro is consistent with our transcriptomic data results. This study affirms that paracrine dysregulation of semaphorin3B ligand and plexinA2 /neuropilin1 receptor activity implicates glomerular injury. Because SEMA3B activity is downregulated both in vivo and in vitro - we may conclude that SEMA3B dysregulation is not only associated, but a causative factor in glomerular sensitization.