Muc1 is protective during kidney ischemia-reperfusion injury

Abstract

Ischemia-reperfusion injury (IRI) due to hypotension is a common cause of human acute kidney injury (AKI). Hypoxia-inducible transcription factors (HIFs) orchestrate a protective response in renal endothelial and epithelial cells in AKI models. As human mucin 1 (MUC1) is induced by hypoxia and enhances HIF-1 activity in cultured epithelial cells, we asked whether mouse mucin 1 (Muc1) regulates HIF-1 activity in kidney tissue during IRI. Whereas Muc1 was localized on the apical surface of the thick ascending limb, distal convoluted tubule, and collecting duct in the kidneys of sham-treated mice, Muc1 appeared in the cytoplasm and nucleus of all tubular epithelia during IRI. Muc1 was induced during IRI, and Muc1 transcripts and protein were also present in recovering proximal tubule cells. Kidney damage was worse and recovery was blocked during IRI in Muc1 knockout mice compared with congenic control mice. Muc1 knockout mice had reduced levels of HIF-1α, reduced or aberrant induction of HIF-1 target genes involved in the shift of glucose metabolism to glycolysis, and prolonged activation of AMP-activated protein kinase, indicating metabolic stress. Muc1 clearly plays a significant role in enhancing the HIF protective pathway during ischemic insult and recovery in kidney epithelia, providing a new target for developing therapies to treat AKI. Moreover, our data support a role specifically for HIF-1 in epithelial protection of the kidney during IRI as Muc1 is present only in tubule epithelial cells.

Novel roles for mucin 1 in the kidney

“…Deep sequencing of microdissected adult rat renal tubule segments revealed that MUC1 was present in collecting duct (CD)> medullary loop of Henle> thick ascending limb (TAL)> distal convoluted tubule (DCT)≫≫ PT (based on RPKM) [45]. We also found the highest levels of Muc1 in the DCT, CD and TAL in the kidneys of sham treated mice using immunohistochemistry (IHC), but we also found Muc1 staining at very low levels in the PT that was absent in the Muc1 KO mouse kidney [31]. Muc1 appeared in the cytoplasm of all tubule epithelia immediately after 19 min ischemia, and was found in the nuclei after 4 h recovery [31].…”

“…We also found the highest levels of Muc1 in the DCT, CD and TAL in the kidneys of sham treated mice using immunohistochemistry (IHC), but we also found Muc1 staining at very low levels in the PT that was absent in the Muc1 KO mouse kidney [31]. Muc1 appeared in the cytoplasm of all tubule epithelia immediately after 19 min ischemia, and was found in the nuclei after 4 h recovery [31]. Total Muc1 levels as assessed by immunblotting kidney homogenates was increased 4.2-fold after 3 d recovery when Muc1 staining by IHC was observed on the apical surface of flattened cells in the recovering proximal tubule [31].…”

“…Muc1 appeared in the cytoplasm of all tubule epithelia immediately after 19 min ischemia, and was found in the nuclei after 4 h recovery [31]. Total Muc1 levels as assessed by immunblotting kidney homogenates was increased 4.2-fold after 3 d recovery when Muc1 staining by IHC was observed on the apical surface of flattened cells in the recovering proximal tubule [31]. The appearance of Muc1 on the apical surface of the recovering PT at 3 d recovery is even more convincing using immunofluorescence microscopy and co-staining with antibodies against the organic ion transporter 1 (OAT1) localized on the basolateral surface (Fig.…”

“…While sepsis does stress the kidney primarily by indirect means, the most well characterized model of acute kidney injury is produced by clamping both the renal artery and vein, or the artery alone, to produce ischemia, and studying recovery of kidney function and morphology after return of blood flow for hours to days [28-30]. Using this approach, we found that Muc1 is protective in the kidney in a mouse model of ischemia-reperfusion injury by transactivation of the HIF-1 and β-catenin protective pathways [31,32]. …”

Insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinases-2: differential expression and secretion in human kidney tubule cells

“…Cells of proximal tubule origin were isolated using an antibody directed against APN, which is expressed across the proximal nephron and is a marker that has been used previously for immunoaffinity isolation of proximal tubule cells from human tissue (6,67,68). Cells of distal tubule origin were isolated using an antibody against the sialomucin MUC-1, which is expressed in the TAL, DCT, and CCD (5,10,43). We routinely isolated only 10 -15% of cells from the total heterogeneous pool with either antibody, and the isolated cells were able to be passaged five to seven times before loss of proliferative ability.…”