A novel immunofluorescence detection method for renal cell-type specific in situ cytokine production by confocal microscopy

The study of intercalated cells using ex vivo techniques: primary cell culture, cell lines, kidney slices, and organoids

This review summarizes methods to study kidney intercalated cell (IC) function ex vivo. While important for acid-base homeostasis, IC dysfunction is often not recognized clinically until it becomes severe. The advantage of using ex vivo techniques is that they allow for the differential evaluation of IC function in controlled environments. Although in vitro kidney tubular perfusion is a classical ex vivo technique to study IC, here we concentrate on primary cell cultures, immortalized cell lines, and ex vivo kidney slices. Ex vivo techniques are useful in evaluating IC signaling pathways that allow rapid responses to extracellular changes in pH, CO2, and bicarbonate (HCO3-). However, these methods for IC work can also be challenging, as cell lines that recapitulate IC do not proliferate easily in culture. Moreover, a "pure" IC population in culture does not necessarily replicate its collecting duct (CD) environment, where ICs are surrounded by the more abundant principal cells (PCs). It is reassuring that many findings obtained in ex vivo IC systems signaling have been largely confirmed in vivo. Some of these newly identified signaling pathways reveal that ICs are important for regulating NaCl reabsorption, thus suggesting new frontiers to target antihypertensive treatments. Moreover, recent single-cell characterization studies of kidney epithelial cells revealed a dual developmental origin of IC, as well as the presence of novel CD cell types with certain IC characteristics. These exciting findings present new opportunities for the study of IC ex vivo and will likely rediscover the importance of available tools in this field.NEW & NOTEWORTHY The study of kidney intercalated cells has been limited by current cell culture and kidney tissue isolation techniques. This review is to be used as a reference to select ex vivo techniques to study intercalated cells. We focused on the use of cell lines and kidney slices as potential useful models to study membrane transport proteins. We also review how novel collecting duct organoids may help better elucidate the role of these intriguing cells.

Transient depletion of macrophages alters local inflammatory response at the site of disc herniation in a transgenic mouse model

OBJECTIVE

Macrophages are abundantly detected at sites of disc herniation, however, their function in the disease progression is unclear. We aim to investigate the functions of macrophages in acute disc herniation using a macrophage Fas-induced apoptosis (MaFIA) transgenic mouse strain.

METHOD

To transiently deplete macrophages, a dimerizer, AP20187, or vehicle solution was administered via intraperitoneal injection to MaFIA mice immediately, day 1 and 2 after annular puncture induced disc herniation. Local infiltrated tissues at disc hernia and DRGs at corresponding levels were harvested to analyze immune cells and neuroinflammation on postoperative day (POD) 6 by flow cytometry and/or immunostaining. Mouse spines were harvested to analyze structures of degenerated discs and adjacent vertebrae and to assess osteoclast activity by histology and tartrate-resistant acid phosphatase (TRAP) staining on POD 6, 13, and 20, respectively.

RESULTS

On POD 6, abundant macrophages were confirmed at disc hernia sites. Compared to vehicle control, AP20187 significantly reduced GFP+ cells in blood, spleen, and local inflammatory tissue. At disc hernia sites, AP20187 markedly reduced macrophages (CD11b+, F4/80+, GFP+CD11b+, CD11b+F4/80+) while increasing neutrophils and B cells. Transient macrophage depletion decreased ectopic bone formation and osteoclast activity in herniated discs and adjacent cortical bones for up to 20 days post herniation. Disc herniation elevated expressions of TNF-α, IL-6, substance P, calcitonin gene-related peptide, accompanied by increasing GFP+, CD11b+ and F4/80+ macrophages. Macrophage depletion did not attenuate these markers of neuroinflammation.

CONCLUSIONS

Transient depletion of macrophages altered local inflammatory response at the site of disc herniation.