Identification and classification of interstitial cells in the mouse renal pelvis

Abstract

Key points Platelet-derived growth factor receptor-alpha (PDGFR alpha) is a novel biomarker along with smooth myosin heavy chain for the pacemaker cells (previously termed 'atypical' smooth muscle cells) in the murine and cynomolgus monkey pelvis-kidney junction. PDGFR alpha(+) cells present in adventitial and urothelial layers of murine renal pelvis do not express smooth muscle myosin heavy chain (smMHC) but are in close apposition to nerve fibres. Most c-Kit(+) cells in the renal pelvis are mast cells. Mast cells (CD117(+)/CD45(+)) are more abundant in the proximal renal pelvis and pelvis-kidney junction regions whereas c-Kit(+) interstitial cells (CD117(+)/CD45(-)) are found predominantly in the distal renal pelvis and ureteropelvic junction. PDGFR alpha(+) cells are distinct from c-Kit(+) interstitial cells. A subset of PDGFR alpha(+) cells express the Ca2+-activated Cl- channel, anoctamin-1, across the entire renal pelvis. Spontaneous Ca2+ transients were observed in c-Kit(+) interstitial cells, smMHC(+) PDGFR alpha cells and smMHC(-) PDGFR alpha cells using mice expressing genetically encoded Ca2+ sensors. Rhythmic contractions of the renal pelvis transport urine from the kidneys into the ureter. Specialized pacemaker cells, termed atypical smooth muscle cells (ASMCs), are thought to drive the peristaltic contractions of typical smooth muscle cells (TSMCs) in the renal pelvis. Interstitial cells (ICs) in close proximity to ASMCs and TSMCs have been described, but the role of these cells is poorly understood. The presence and distributions of platelet-derived growth factor receptor-alpha(+) (PDGFR alpha(+)) ICs in the pelvis-kidney junction (PKJ) and distal renal pelvis were evaluated. We found PDGFR alpha(+) ICs in the adventitial layers of the pelvis, the muscle layer of the PKJ and the adventitia of the distal pelvis. PDGFR alpha(+) ICs were distinct from c-Kit(+) ICs in the renal pelvis. c-Kit(+) ICs are a minor population of ICs in murine renal pelvis. The majority of c-Kit(+) cells were mast cells. PDGFR alpha(+) cells in the PKJ co-expressed smooth muscle myosin heavy chain (smMHC) and several other smooth muscle gene transcripts, indicating these cells are ASMCs, and PDGFR alpha is a novel biomarker for ASMCs. PDGFR alpha(+) cells also express Ano1, which encodes a Ca2+-activated Cl- conductance that serves as a primary pacemaker conductance in ICs of the GI tract. Spontaneous Ca2+ transients were observed in c-Kit(+) ICs, smMHC(+) PDGFR alpha cells and smMHC(-) PDGFR alpha cells using genetically encoded Ca2+ sensors. A reporter strain of mice with enhanced green fluorescent protein driven by the endogenous promotor for Pdgfra was shown to be a powerful new tool for isolating and characterizing the phenotype and functions of these cells in the renal pelvis.