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Megalin knockout mice as an animal model of low molecular weight proteinuria.

ABSTRACT: Megalin is an endocytic receptor expressed on the luminal surface of the renal proximal tubules. The receptor is believed to play an important role in the tubular uptake of macromolecules filtered through the glomerulus. To elucidate the role of megalin in vivo and to identify its endogenous ligands, we analyzed the proximal tubular function in mice genetically deficient for the receptor. We demonstrate that megalin-deficient mice exhibit a tubular resorption deficiency and excrete low molecular weight plasma proteins in the urine (low molecular weight proteinuria). Proteins excreted include small plasma proteins that carry lipophilic compounds including vitamin D-binding protein, retinol-binding protein, alpha(1)-microglobulin and odorant-binding protein. Megalin binds these proteins and mediates their cellular uptake. Urinary loss of carrier proteins in megalin-deficient mice results in concomitant loss of lipophilic vitamins bound to the carriers. Similar to megalin knockout mice, patients with low molecular weight proteinuria as in Fanconi syndrome are also shown to excrete vitamin/carrier complexes. Thus, these results identify a crucial role of the proximal tubule in retrieval of filtered vitamin/carrier complexes and the central role played by megalin in this process.

SUBMITTER: Leheste JR

PROVIDER: S-EPMC1867027 | biostudies-literature | 1999 Oct

REPOSITORIES: biostudies-literature

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Megalin knockout mice as an animal model of low molecular weight proteinuria.

Leheste J R JR Rolinski B B Vorum H H Hilpert J J Nykjaer A A Jacobsen C C Aucouturier P P Moskaug J O JO Otto A A Christensen E I EI Willnow T E TE

The American journal of pathology 19991001 4

Megalin is an endocytic receptor expressed on the luminal surface of the renal proximal tubules. The receptor is believed to play an important role in the tubular uptake of macromolecules filtered through the glomerulus. To elucidate the role of megalin in vivo and to identify its endogenous ligands, we analyzed the proximal tubular function in mice genetically deficient for the receptor. We demonstrate that megalin-deficient mice exhibit a tubular resorption deficiency and excrete low molecular ...[more]

PMID: 10514418

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Project description:BackgroundColorectal cancer is a malignant gastrointestinal cancer, in which some advanced patients would develop cancer cachexia (CAC). CAC is defined as a multi-factorial syndrome characterized by weight loss and muscle loss (with or without fat mass), leading to progressive dysfunction, thereby increasing morbidity and mortality. ApcMin/+ mice develop spontaneous intestinal adenoma, which provides an established model of colorectal cancer for CAC study. Upon studying the ApcMin/+ mouse model, we observed a marked decrease in weight gain beginning around week 15. Such a reduction in weight gain was rescued when ApcMin/+ mice were crossed with MMP12-/- mice, indicating that MMP12 has a role in age-related ApcMin/+-associated weight loss. As a control, the weight of MMP12-/- mice on a weekly basis, their weight were not significantly different from those of WT mice.MethodsApcMin/+; MMP12-/- mice were obtained by crossing ApcMin/+ mice with MMP12 knockout (MMP12 -/-) mice. Histological scores were assessed using hematoxylin-eosin (H&E) staining. MMP12 expression was confirmed by immunohistochemistry and immunofluorescence staining. ELISA, protein microarrays and quantitative Polymerase Chain Reaction (qPCR) were used to investigate whether tumor could up-regulate IL-6. Cell-based assays and western blot were used to verify the regulatory relationship between IL-6 and MMP12. Fluorescence intensity was measured to determine whether MMP12 is associated with insulin and insulin-like growth factor 1 (IGF-1) in vitro. MMP12 inhibitors were used to explore whether MMP12 could affect the body weight of ApcMin/+ mice.ResultsMMP12 knockout led to weight gain and expansion of muscle fiber cross-sectional area (all mice had C57BL/6 background) in ApcMin/+ mice, while inhibiting MMP12 could suppress weight loss in ApcMin/+ mice. MMP12 was up-regulated in muscle tissues and peritoneal macrophages of ApcMin/+ mice. IL-6 in tumor cells and colorectal cancer patients is up-regulation. IL-6 stimulated MMP12 secretion of macrophage.ConclusionsMMP12 is essential for controlling body weight of Apc Min/+ mice. Our study shows that it exists the crosstalk between cancer cells and macrophages in muscle tissues that tumor cells secrete IL-6 inducing macrophages to up-regulate MMP12. This study may provide a new perspective of MMP12 in the treatment for weight loss induced by CAC.

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Megalin knockout mice as an animal model of low molecular weight proteinuria.

Publications

Megalin knockout mice as an animal model of low molecular weight proteinuria.

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