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Insulin-like growth factor (IGF)-II- mediated fibrosis in pathogenic lung conditions.

ABSTRACT: Type 2 insulin-like growth factor (IGF-II) levels are increased in fibrosing lung diseases such as idiopathic pulmonary fibrosis (IPF) and scleroderma/systemic sclerosis-associated pulmonary fibrosis (SSc). Our goal was to investigate the contribution of IGF receptors to IGF-II-mediated fibrosis in these diseases and identify other potential mechanisms key to the fibrotic process. Cognate receptor gene and protein expression were analyzed with qRT-PCR and immunoblot in primary fibroblasts derived from lung tissues of normal donors (NL) and patients with IPF or SSc. Compared to NL, steady-state receptor gene expression was decreased in SSc but not in IPF. IGF-II stimulation differentially decreased receptor mRNA and protein levels in NL, IPF, and SSc fibroblasts. Neutralizing antibody, siRNA, and receptor inhibition targeting endogenous IGF-II and its primary receptors, type 1 IGF receptor (IGF1R), IGF2R, and insulin receptor (IR) resulted in loss of the IGF-II response. IGF-II tipped the TIMP:MMP balance, promoting a fibrotic environment both intracellularly and extracellularly. Differentiation of fibroblasts into myofibroblasts by IGF-II was blocked with a TGFβ1 receptor inhibitor. IGF-II also increased TGFβ2 and TGFβ3 expression, with subsequent activation of canonical SMAD2/3 signaling. Therefore, IGF-II promoted fibrosis through IGF1R, IR, and IGF1R/IR, differentiated fibroblasts into myofibroblasts, decreased protease production and extracellular matrix degradation, and stimulated expression of two TGFβ isoforms, suggesting that IGF-II exerts pro-fibrotic effects via multiple mechanisms.

SUBMITTER: Garrett SM

PROVIDER: S-EPMC6876936 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Our previous studies showed that Insulin-like Growth Factor (IGF)-1 reduced blood brain barrier permeability and decreased infarct volume caused by middle cerebral artery occlusion (MCAo) in middle aged female rats. Similarly, cultures of primary brain microvessel endothelial cells from middle-aged female rats and exposed to stroke-like conditions (oxygen glucose deprivation; OGD) confirmed that IGF-1 reduced dye transfer across this cell monolayer. Surprisingly, IGF-1 did not attenuate endothelial cell death caused by OGD. To reconcile these findings, the present study tested the hypothesis that, at the earliest phase of ischemia, IGF-1 promotes barrier function by increasing anchorage and stabilizing cell geometry of surviving endothelial cells. Cultures of human brain microvessel endothelial cells were subject to oxygen-glucose deprivation (OGD) in the presence of IGF-1, IGF-1?+?JB-1 (IGFR inhibitor) or vehicle. OGD disrupted the cell monolayer and reduced cell-cell interactions, which was preserved in IGF-1-treated cultures and reversed by concurrent treatment with JB-1. IGF-1-mediated preservation of the endothelial monolayer was reversed with LY294002 treatment, but not by Rapamycin, indicating that IGF-1?s actions on cell-cell contacts are likely mediated via the PI3K pathway. In vivo, microvessel morphology was evaluated in middle-aged female rats that were subjected to ischemia by MCAo, and treated ICV with IGFI, IGF-1?+?JB-1, or artificial CSF (aCSF; vehicle) after reperfusion. Compared to vehicle controls, IGF-1 treated animals displayed larger microvessel diameters in the peri-infarct area and increased staining density for vinculin, an anchorage protein. Both these measures were reversed by concurrent IGF-1?+?JB-1 treatment. Moreover these effects were restricted to 24?h after ischemia-reperfusion and no treatment effects were seen at 5d post stroke. Collectively, these data suggest that in the earliest hours during ischemia, IGF-1 promotes receptor-mediated anchorage of endothelial cells, and its actions may be accurately characterized as vasculoprotective.

Project description:The binding affinities of seven analogues of recombinant human insulin-like growth factor II (hIGF-II) were characterized for the IGF type-I and type-II receptors and insulin receptors, as well as for IGF-binding protein (IGFBP)-1, IGFBP-2, IGFPB-3 and human serum IGFBPs. A switch of two of the three cysteine bridges in hIGF-II, 9-47 and 46-51 to 9-46 and 47-51, severely impaired the binding of this analogue to all receptors and to the IGFBPs. The affinities for the IGF type-I receptor and the IGFBPs were decreased over 100-fold, while the binding to the insulin receptor and the IGF type-II receptor was less affected, with a 6-10-fold decrease in affinity. Slight modifications of the N-terminus had only minor effects upon the binding of hIGF-II to the IGFBPs or to the receptors. Deletion of both the N-terminal amino acid and the two C-terminal amino acids resulted in moderate decreases in affinity, with a 60% decrease in affinity for IGFBP-1 and the IGF type-I receptor. Acetylation of the N-terminus of Ala1 and the epsilon-nitrogen of Lys65 decreased the affinity, by 60-90%, of hIGF-II for all of the IGFBPs and receptors. The experiments involving acetylation of IGF-II or switching of its cysteine bridges indicated that these modifications (no substitution, deletion or addition of any of the 67 amino acids of hIGF-II) may lead to a severe impairment of the binding affinity of IGF-II for both the IGFBPs and the receptors. Acetylation of the epsilon-nitrogen of Lys65, which causes a charge change, or alteration of the three-dimensional structure, as shown by the cysteine bridge switch, lead to a severe impairment of the binding affinity for the binding proteins and for the receptors. In general, care should be taken with the synthesis of analogues and the interpretation of resulting binding data, since affinity alterations ascribed to amino acid changes may instead be caused by alterations of the charge or the three-dimensional structure of the protein.

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Insulin-like growth factor (IGF)-II- mediated fibrosis in pathogenic lung conditions.

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