Tissue-resident memory T cells in renal autoimmune diseases

The discovery of tissue-resident memory T cells (TRM cells) reinterpreted the potential of human tissue-specific immunity. Following T cell receptor (TCR) activation and clonal expansion, effector T cells migrate to peripheral tissues where they remain long-term and differentiate to TRM cells after antigen clearance. This allows for prompt immunological responses upon antigen re-encounter. In addition to their protective properties in acute infections, recent studies have revealed that TRM cells might lead to aggravation of autoimmune diseases, such as lupus nephritis (LN) and anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN). These diseases present as proliferative and crescentic glomerulonephritis (cGN), which is a life-threatening condition leading to end-stage renal disease (ESRD) if left untreated. A better understanding of renal TRM cells might lead to identifying new therapeutic targets for relapsing autoimmune diseases of the kidney. In this review, we summarize the current knowledge of renal TRM cells and discuss their potential pathophysiological roles in renal autoimmune diseases

Dysfunction of fibroblasts of extrarenal origin underlies renal fibrosis and renal anemia in mice

In chronic kidney disease, fibroblast dysfunction causes renal fibrosis and renal anemia. Renal fibrosis is mediated by the accumulation of myofibroblasts, whereas renal anemia is mediated by the reduced production of fibroblast-derived erythropoietin, a hormone that stimulates erythropoiesis. Despite their importance in chronic kidney disease, the origin and regulatory mechanism of fibroblasts remain unclear. Here, we have demonstrated that the majority of erythropoietin-producing fibroblasts in the healthy kidney originate from myelin protein zero–Cre (P0-Cre) lineage-labeled extrarenal cells, which enter the embryonic kidney at E13.5. In the diseased kidney, P0-Cre lineage-labeled fibroblasts, but not fibroblasts derived from injured tubular epithelial cells through epithelial-mesenchymal transition, transdifferentiated into myofibroblasts and predominantly contributed to fibrosis, with concomitant loss of erythropoietin production. We further demonstrated that attenuated erythropoietin production in transdifferentiated myofibroblasts was restored by the administration of neuroprotective agents, such as dexamethasone and neurotrophins. Moreover, the in vivo administration of tamoxifen, a selective estrogen receptor modulator, restored attenuated erythropoietin production as well as fibrosis in a mouse model of kidney fibrosis. These findings reveal the pathophysiological roles of P0-Cre lineage-labeled fibroblasts in the kidney and clarify the link between renal fibrosis and renal anemia

Bmp7 inhibits the differentiation of cap mesenchyme in kidney explant culture.

<p>Kidney explants were taken from Bmp7^LacZ/fl;Gt(ROSA)26Sor^CreERT2 embryos at E12.5 and cultured for 72 h in the presence or absence of 4-OHT. The expression of Bmp7 mRNA was significantly reduced in Bmp7^LacZ/fl;Gt(ROSA)26Sor^CreERT2 explants treated with 4-OHT compared to the explants from the same embryos treated with a vehicle (n = 3). Data are represented as mean ± SD. Whole explants were costained with pan-cytokeratin (green) to label ureteric buds and Jagged1 (red) to label developing nephrons. The Jagged1-positive red area was measured utilizing Photoshop software. In Bmp7^LacZ/fl;Gt(ROSA)26Sor^CreERT2 explants treated with 4-OHT, Jagged1-positive regions were significantly expanded, indicating accelerated differentiation. Scale bars: 100 µm.</p

Acceleration of nephron maturation and reduction of cap mesenchyme at E18.5 in Bmp7 knockout kidneys.

<p>(<b>A</b>) Pregnant mothers bearing Bmp7^LacZ/fl;Gt(ROSA)26Sor^CreERT2 and Bmp7^+/fl;Gt(ROSA)26Sor^CreERT2 embryos were administered tamoxifen at E12.5, and sacrificed at E18.5. (<b>B</b>) The expression of Bmp7 mRNA was significantly reduced in knockout kidneys (n = 4, white column) compared to control kidneys (n = 3, black column). Data are represented as mean ± SD. (<b>C and D</b>) Bmp7 knockout embryos at E18.5 exhibited small kidneys. (<b>E and F</b>) The number of cap mesenchymal cells, as shown by the immunostaining of WT1, was decreased in Bmp7 knockout kidneys. (<b>G</b>) The number of phospho-Histone H3-positive cells was reduced in Bmp7 knockout kidneys. pHistone H3 denotes phospho-Histone H3. (<b>H</b>) TUNEL-positive mesenchymal cells were increased in Bmp7 knockout kidneys. (<b>I</b>) The number of TUNEL-positive mesenchymal cells per section was increased in knockout kidneys (white column) compared to control kidneys (black column). Data are represented as mean ± SD. The average numbers of TUNEL-positive mesenchymal cells in three sections were used as the values for each embryo. The mean of the values from three embryos is presented in the graph. (<b>J</b>) Inappropriately “mature” glomeruli were observed in Bmp7 knockout kidneys. (<b>K</b>) Glomeruli in the mature stages were increased in Bmp7 knockout kidneys (white column) compared to the control kidneys (black column). Criteria for the assessment of glomerular maturity are detailed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073554#s4" target="_blank">method</a> section. Because stage I is the most common in control kidneys at E18.5, we summed up the glomeruli of stages II and III for comparison of maturation. Glomeruli were counted in 3 slices of each kidney. The mean of the values ± SD is presented in the graphs (n = 4 for control embryos, and 6 for knockout embryos). (<b>L</b>) Kidneys were stained with LTA (green) and WT1 (red) to label proximal tubules and glomeruli, respectively. The volume of LTA-positive proximal tubule sections in knockout kidneys was comparable to the control kidneys, whereas the number of glomeruli was significantly reduced. (<b>M</b>) The number of LTA⁺ proximal tubule cross sections normalized by the number of WT1⁺ glomeruli was increased in knockout kidneys (white column) compared to control kidneys (black column). Data are represented as mean ± SD. At least three sections were stained for each kidney. The sum of the number of LTA-positive proximal tubule cross sections was divided by the sum of the number of WT1-positive glomeruli. The mean of the values from four embryos is presented in the graph. Scale bars: 100 µm (<b>D, G, L</b>) or 50 µm (<b>E, F, H, J</b>).</p

Acceleration of nephron maturation and apoptosis of cap mesenchyme at E14.5 in Bmp7 knockout kidneys.

<p>(<b>A</b>) Pregnant mothers bearing Bmp7^LacZ/fl;Gt(ROSA)26Sor^CreERT2 and Bmp7^+/fl;Gt(ROSA)26Sor^CreERT2 embryos were administered tamoxifen at E12.5, and sacrificed at E14.5. (<b>B</b>) The expression of Bmp7 mRNA was significantly reduced at E14.5 in Bmp7^LacZ/fl;Gt(ROSA)26Sor^CreERT2 (Bmp7 knockout kidneys) (n = 4, white column) compared to control kindeys (n = 5, black column). Data are represented as mean ± SD. (<b>C and D</b>) Cap mesenchyme was maintained in both Bmp7 knockout kidneys and control kidneys. (<b>E</b>) Cap mesenchyme positive for WT1 was maintained in both genotypes. (<b>F</b>) The distribution and the number of phospho-Histone H3-positive cells were comparable in both genotypes. pHistone H3 denotes phospho-Histone H3. (<b>G</b>) TUNEL-positive cells were increased in Bmp7 knockout kidneys. (<b>H</b>) The number of TUNEL-positive mesenchymal cells per section was increased in knockout kidneys (white column) compared to control kidneys (black column). Data are represented as mean ± SD. The average numbers of TUNEL-positive mesenchymal cells in three sections were used as the values for each embryo. The mean of the values from three embryos is presented in the graph. (<b>I</b>) Bmp7 knockout kidneys exhibited inappropriately “mature” glomeruli at E14.5. (<b>J</b>) Glomeruli in the mature stages were increased in Bmp7 knockout kidneys (white column) compared to the control kidneys (black column). Criteria for the assessment of glomerular maturity are detailed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073554#s4" target="_blank">method</a> section. Because C stage is the most common in control kidneys at E14.5, we summed up the glomeruli of stages I, II, and III for comparison of maturation. Glomeruli were counted in 5 slices of each kidney. The mean of the values ± SD is presented in the graphs (n = 7 for control embryos, and 5 for knockout embryos). Scale bars: 100 µm (<b>C, F, G</b>) or 50 µm (<b>D, E, I</b>). n.s.: not significant.</p