A simple method to fluorescently label pericytes in the CNS and skeletal muscle

Adenosine A1 Receptor Deficiency Aggravates Extracellular Matrix Accumulation in Diabetic Nephropathy through Disturbance of Peritubular Microenvironment

BACKGROUND

We previously observed that adenosine A1 receptor (A1AR) had a protective role in proximal tubular megalin loss associated with albuminuria in diabetic nephropathy (DN). In this study, we aimed to explore the role of A1AR in the fibrosis progression of DN.

METHODS

We collected DN patients' samples and established a streptozotocin-induced diabetes model in wild-type (WT) and A1AR-deficient (A1AR^-/-) mice. The location and expression of CD34, PDGFRβ, and A1AR were detected in kidney tissue samples from DN patients by immunofluorescent and immunohistochemical staining. We also analyzed the expression of TGFβ, collagen (I, III, and IV), α-SMA, and PDGFRβ using immunohistochemistry in WT and A1AR^-/- mice. CD34 and podoplanin expression were analyzed by Western blotting and immunohistochemical staining in mice, respectively. Human renal proximal tubular epithelial cells (HK2) were cultured in medium containing high glucose and A1AR agonist as well as antagonist.

RESULTS

In DN patients, the expression of PDGFRβ was higher with the loss of CD34. The location of PDGFRβ and TGFβ was near to each other. The A1AR, which was colocalized with CD34 partly, was also upregulated in DN patients. In WT-DN mice, obvious albuminuria and renal pathological leisure were observed. In A1AR^-/- DN mice, more severe renal tubular interstitial fibrosis and more extracellular matrix deposition were observed, with lower CD34 expression and pronounced increase of PDGFRβ. In HK2 cells, high glucose stimulated the epithelial-mesenchymal transition (EMT) process, which was inhibited by A1AR agonist.

CONCLUSION

A1AR played a critical role in protecting the tubulointerstitial fibrosis process in DN by regulation of the peritubular microenvironment.

A nuclear fluorescent dye identifies pericytes at the neurovascular unit

Perivascular pericytes are key regulators of the blood-brain barrier, vascular development, and cerebral blood flow. Deciphering pericyte roles in health and disease requires cellular tracking; yet, pericyte identification remains challenging. A previous study reported that the far-red fluorophore TO-PRO-3 (642/661), usually employed as a nuclear dye in fixed tissue, was selectively captured by live pericytes from the subventricular zone. Herein, we validated TO-PRO-3 as a specific pericyte tracer in the nervous system (NS). Living pericytes from ex vivo murine hippocampus, cortex, spinal cord, and retina robustly incorporated TO-PRO-3. Classical pericyte immunomarkers such as chondroitin sulphate proteoglycan neuron-glial antigen 2 (NG2) and platelet-derived growth factor receptor beta antigen (PDGFrβ) and the new pericyte dye NeuroTrace 500/525 confirmed cellular specificity of dye uptake. The TO-PRO-3 signal enabled quantification of pericytes density and morphometry; likewise, TO-PRO-3 labeling allowed visualization of pericytes associated with other components of the neurovascular unit. A subset of TO-PRO-3 stained cells expressed the contractile protein α-SMA, indicative of their ability to control the capillary diameter. Uptake of TO-PRO-3 was independent of connexin/pannexin channels but was highly sensitive to temperature and showed saturation, suggesting that a yet unidentified protein-mediated active transport sustained dye incorporation. We conclude that TO-PRO-3 labeling provides a reliable and simple tool for the bioimaging of pericytes in the murine NS microvasculature.

Platelet-derived growth factor receptor-β expression in human peritoneum

INTRODUCTION

Simple peritoneal fibrosis and encapsulating peritoneal sclerosis (EPS) are important lesions in the peritoneum of patients on peritoneal dialysis (PD). We have previously described a population of podoplanin-positive myofibroblasts in peritoneal biopsies from patients with EPS. Platelet-derived growth factor receptor-β (PDGFRβ) is a marker of pericytes, and PDGFs might be involved in the fibrotic response of the peritoneum. This study aimed to describe PDGFRβ in the human peritoneum.

METHODS

In this retrospective analysis, we localized PDGFRβ in peritoneal biopsies from patients with EPS (n = 6) and patients on PD without signs of EPS (n = 5), and compared them with normal peritoneum (n = 4) and peritoneum from uremic patients (n = 5). Consecutive sections were stained for smooth-muscle actin (SMA) and podoplanin. Slides were scored semiquantitatively by 2 observers blinded to the diagnosis.

RESULTS

PDGFRβ was expressed by cells of arterial walls in all biopsies. A prominent population of PDGFRβ-positive cells was present in the normal peritoneum, which were SMA negative on consecutive sections. In patients on PD, a high number of PDGFRβ were also positive for SMA. In EPS, the majority of podoplanin-positive cells were positive for PDGFRβ. In peritoneal biopsies from normal and uremic patients, the expression of SMA was mainly restricted to cells of arterial walls. Podoplanin expression was restricted to lymphatic vessels in normal peritoneum, in uremic patients, and in patients on PD without EPS.

CONCLUSIONS

As podoplanin-positive myofibroblasts express PDGFRβ, these cells might be related to pericytes (rather than other sources of fibroblasts). PDGFRβ might turn out to be a therapeutic target in EPS.