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Hypoxia-inducible factor signaling in the development of kidney fibrosis.

Haase VH - Fibrogenesis Tissue Repair (2012)

Bottom Line: A discrepancy between oxygen availability and demand has been found in most chronic kidney diseases (CKD) irrespective of etiology.Consistent with decreased renal oxygenation in CKD is the increased expression of the oxygen-sensitive α-subunit of hypoxia-inducible factor (HIF)-1.Cell type-specific functions of individual HIF transcription factors and their relevant transcriptional targets are discussed in the context of renal fibrogenesis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Nephrology and Hypertension, Departments of Medicine, Molecular Physiology and Biophysics, and Cancer Biology, Vanderbilt School of Medicine, Nashville, TN, USA.

ABSTRACT
A discrepancy between oxygen availability and demand has been found in most chronic kidney diseases (CKD) irrespective of etiology. This results from a combination of structural and functional changes that are commonly associated with the development of fibrosis, which include a reduction in peritubular blood flow, luminal narrowing of atherosclerotic vessels, capillary rarefaction and vascular constriction due to altered expression of vasoactive factors and signaling molecules (e.g. angiotensin II, endothelin, nitric oxide). Consistent with decreased renal oxygenation in CKD is the increased expression of the oxygen-sensitive α-subunit of hypoxia-inducible factor (HIF)-1. HIF transcription factors are members of the Per-ARNT-Sim (PAS) family of heterodimeric basic helix-loop-helix transcription factors and consist of an oxygen-sensitive α-subunit and a constitutively expressed β-unit, also known as the aryl-hydrocarbon-receptor nuclear translocator (ARNT) or HIF-β. Recent experimental evidence suggests that prolonged activation of HIF signaling in renal epithelial cells enhances maladaptive responses, which lead to fibrosis and further tissue destruction. Cell type-specific functions of individual HIF transcription factors and their relevant transcriptional targets are discussed in the context of renal fibrogenesis.

No MeSH data available.


Related in: MedlinePlus

LOX inhibition impairs migration of primary renal epithelial cells in vitro. Cells were cultured under hypoxia for 6 days, 2 h prior to placing a scratch wound, lysyl oxidase inhibitors BAPN or BCS were added and cell migration monitored over 30 h. Hx: Control cells (hypoxia without inhibitor). Magnification ×100.
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Figure 4: LOX inhibition impairs migration of primary renal epithelial cells in vitro. Cells were cultured under hypoxia for 6 days, 2 h prior to placing a scratch wound, lysyl oxidase inhibitors BAPN or BCS were added and cell migration monitored over 30 h. Hx: Control cells (hypoxia without inhibitor). Magnification ×100.

Mentions: An important cellular process, which is associated with the development of tubulointerstitial fibrosis, is EMT [21-23]. EMT in the setting of CKD is considered a disease-promoting process by which epithelial cells acquire a mesenchymal phenotype and then migrate into the interstitial compartment through breaks in the basement membrane, where they together with resident cells produce extracellular matrix as myofibroblasts [24]. To explore whether EMT in renal tubular epithelial cells is modulated by hypoxia via HIF, we isolated primary tubular epithelial cells (PTECs) from the kidney cortex of genetically modified mice, which express a tetracycline-inducible Cre-recombinase permitting inactivation of HIF-1α in vitro. Using this approach, we demonstrated that hypoxia (1% O2) led to morphologic and gene expression changes that were consistent with EMT, and furthermore enhanced the migratory ability of PTECs in a HIF-1-dependent fashion. Since HIF-regulation of lysyl oxidase (LOX) was required for hypoxia-induced migration of breast cancer cells [25], we investigated whether lysyl oxidases were involved in mediating the EMT-promoting effects of hypoxia in PTECs. We first established that the hypoxic regulation of LOX and its homologue LOXL2 was HIF-1-dependent, and then used pharmacological means to investigate the effects of lysyl oxidase inhibition on epithelial cell migration. Lysyl oxidase inhibitors β-aminoproprionitrile (BAPN) or bathocuproine disulphate (BCS) phenocopied the effects of HIF-1 inactivation, and attenuated hypoxia-enhanced migration in a scratch wound closure assay; complete closure was observed by 24 hours in hypoxic cells, whereas pre-treatment with either BAPN or BCS inhibited migration with the scratch not closing for at least 30 hours (Figure 4). Lysyl oxidases are copper-dependent enzymes with intracellular and extracellular activities, and catalyze the oxidation of lysine residues in collagen and elastin fibers, thereby modulating cell migration and epithelial differentiation [26,27]. BAPN is an irreversible inhibitor of lysyl oxidases and inhibits all lysyl oxidase family members.


Hypoxia-inducible factor signaling in the development of kidney fibrosis.

Haase VH - Fibrogenesis Tissue Repair (2012)

LOX inhibition impairs migration of primary renal epithelial cells in vitro. Cells were cultured under hypoxia for 6 days, 2 h prior to placing a scratch wound, lysyl oxidase inhibitors BAPN or BCS were added and cell migration monitored over 30 h. Hx: Control cells (hypoxia without inhibitor). Magnification ×100.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368791&req=5

Figure 4: LOX inhibition impairs migration of primary renal epithelial cells in vitro. Cells were cultured under hypoxia for 6 days, 2 h prior to placing a scratch wound, lysyl oxidase inhibitors BAPN or BCS were added and cell migration monitored over 30 h. Hx: Control cells (hypoxia without inhibitor). Magnification ×100.
Mentions: An important cellular process, which is associated with the development of tubulointerstitial fibrosis, is EMT [21-23]. EMT in the setting of CKD is considered a disease-promoting process by which epithelial cells acquire a mesenchymal phenotype and then migrate into the interstitial compartment through breaks in the basement membrane, where they together with resident cells produce extracellular matrix as myofibroblasts [24]. To explore whether EMT in renal tubular epithelial cells is modulated by hypoxia via HIF, we isolated primary tubular epithelial cells (PTECs) from the kidney cortex of genetically modified mice, which express a tetracycline-inducible Cre-recombinase permitting inactivation of HIF-1α in vitro. Using this approach, we demonstrated that hypoxia (1% O2) led to morphologic and gene expression changes that were consistent with EMT, and furthermore enhanced the migratory ability of PTECs in a HIF-1-dependent fashion. Since HIF-regulation of lysyl oxidase (LOX) was required for hypoxia-induced migration of breast cancer cells [25], we investigated whether lysyl oxidases were involved in mediating the EMT-promoting effects of hypoxia in PTECs. We first established that the hypoxic regulation of LOX and its homologue LOXL2 was HIF-1-dependent, and then used pharmacological means to investigate the effects of lysyl oxidase inhibition on epithelial cell migration. Lysyl oxidase inhibitors β-aminoproprionitrile (BAPN) or bathocuproine disulphate (BCS) phenocopied the effects of HIF-1 inactivation, and attenuated hypoxia-enhanced migration in a scratch wound closure assay; complete closure was observed by 24 hours in hypoxic cells, whereas pre-treatment with either BAPN or BCS inhibited migration with the scratch not closing for at least 30 hours (Figure 4). Lysyl oxidases are copper-dependent enzymes with intracellular and extracellular activities, and catalyze the oxidation of lysine residues in collagen and elastin fibers, thereby modulating cell migration and epithelial differentiation [26,27]. BAPN is an irreversible inhibitor of lysyl oxidases and inhibits all lysyl oxidase family members.

Bottom Line: A discrepancy between oxygen availability and demand has been found in most chronic kidney diseases (CKD) irrespective of etiology.Consistent with decreased renal oxygenation in CKD is the increased expression of the oxygen-sensitive α-subunit of hypoxia-inducible factor (HIF)-1.Cell type-specific functions of individual HIF transcription factors and their relevant transcriptional targets are discussed in the context of renal fibrogenesis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Nephrology and Hypertension, Departments of Medicine, Molecular Physiology and Biophysics, and Cancer Biology, Vanderbilt School of Medicine, Nashville, TN, USA.

ABSTRACT
A discrepancy between oxygen availability and demand has been found in most chronic kidney diseases (CKD) irrespective of etiology. This results from a combination of structural and functional changes that are commonly associated with the development of fibrosis, which include a reduction in peritubular blood flow, luminal narrowing of atherosclerotic vessels, capillary rarefaction and vascular constriction due to altered expression of vasoactive factors and signaling molecules (e.g. angiotensin II, endothelin, nitric oxide). Consistent with decreased renal oxygenation in CKD is the increased expression of the oxygen-sensitive α-subunit of hypoxia-inducible factor (HIF)-1. HIF transcription factors are members of the Per-ARNT-Sim (PAS) family of heterodimeric basic helix-loop-helix transcription factors and consist of an oxygen-sensitive α-subunit and a constitutively expressed β-unit, also known as the aryl-hydrocarbon-receptor nuclear translocator (ARNT) or HIF-β. Recent experimental evidence suggests that prolonged activation of HIF signaling in renal epithelial cells enhances maladaptive responses, which lead to fibrosis and further tissue destruction. Cell type-specific functions of individual HIF transcription factors and their relevant transcriptional targets are discussed in the context of renal fibrogenesis.

No MeSH data available.


Related in: MedlinePlus