Renal interstitial cells support proximal tubular regeneration in response to local injury
Authors: Schiessl Ina Maria , Grill Alexandra , Steppan Dominik , Fremter Katharina , Castrop Hayo 
Published: November 2023

Platelet‐derived growth factor chain B (PDGF‐B) and PDGF receptor β (PDGFRβ)‐signalling contribute to epithelial‐interstitial cell communication in many organs and facilitates regenerative functions, such as wound healing and tissue repair. In the kidney, a potential role of interstitial cells in tubular regeneration remains obscure. Here we determined the role of interstitial PDGFRβ+ cells in tubular regeneration by serial intravital multiphoton microscopy and subsequent3‐D reconstruction. We used inducible PDGFRβ‐Cre x Confetti mice, to identify PDGFRβ+ interstitial cells in vivo by membrane‐targeted CFP, nuclear GFP and cytosolic YFP and RFP‐expression. PDGFRβ‐Cre x GCamP5 mice were used to determine intracellular calcium [Ca2+]of interstitial cells. Baseline imaging revealed interstitial PDGFRβ+ cells with dendritic morphology and long cell extensions connecting individual PDGFRβ+ cells and the tubular epithelium. Local tubular injury of 1–2 proximal tubule (PT) cells was induced by high laser exposure and caused an immediate 2‐fold increase of [Ca2+]in those PDGFRβ+ cells, which were located adjacent to the affected PT (n=40, p<.0001). The increase in interstitial PDGFRβ [Ca2+] was unaltered by suramin pre‐treatment (50 mg/kg), remained elevated over the first 72h post injury, and was associated with PDGFRβ‐cell proliferation (monochromatic cell division in PDGFRβ‐Crex Confetti mice). Furthermore, we observed the rapid migration (37.81±5 μm/24 h) of interstitial cells towards the injury site. Within 12–24 h, the injury site was enclosed by recruited PDGFRβ+interstitial cells. The recruitment of interstitial cells to the injury site was accompanied by the flattening of the resident tubular cells, followed by clonal epithelial cell division starting 3 days after injury. The latter was revealed by Pax8 x Confetti mice, which express CFP, GFP, YFP or RFP in all tubular cells. Conversely, we obtained no evidence for the integration of extra‐tubular cells into the tubular epithelium. To further investigate the tubular cell regeneration in response to interstitial cell recruitment, we performed histological analysis of the affected kidney areas. 24 h after the injury, the affected tubular epithelium expressed increased PDGF‐B levels. After 48 h, we found dedifferentiated tubular epithelial cells in the vicinity of the injury site (positive CD44‐staining). Finally, 7 days post injury, the recruited interstitial cells had moved a way from the injury site and had dispersed in the interstitium. There generated PT cells stained positive for CD44 and megalin, and reached 50% of control PT‐cell albumin uptake, as determined in vivo. In summary, our data suggest that renal interstitial cells are motile. Thus, local PT cell injury led to an immediate activation and recruitment of interstitial cells to the injury site. Proximal tubular regeneration was exclusively facilitated by clonal cell division of dedifferentiated resident epithelial cells, suggesting that interstitial cells modulate tubular regeneration rather than integrate into the epithelium. Together, these data suggest a communication between the interstitium and the tubular system, which appears to be functionally relevant for tubular regeneration.

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Deutsche Forschungsgemeinschaft (SFB699/B7)