Parathyroid Hormone Induces Transition of Myofibroblasts in Arteriovenous Fistula and Increases Maturation Failure

Exploring the role of ITGB6: fibrosis, cancer, and other diseases

Integrin β6 (ITGB6), a member of the integrin family of proteins, is only present in epithelial tissues and frequently associates with integrin subunit αv to form transmembrane heterodimers named integrin αvβ6. Importantly, ITGB6 determines αvβ6 expression and availability. In addition to being engaged in organ fibrosis, ITGB6 is also directly linked to the emergence of cancer, periodontitis, and several potential genetic diseases. Therefore, it is of great significance to study the molecular-biological mechanism of ITGB6, which could provide novel insights for future clinical diagnosis and therapy. This review introduces the structure, distribution, and biological function of ITGB6. This review also expounds on ITGB6-related diseases, detailing the known biological effects of ITGB6.

Functions for platelet factor 4 (PF4/CXCL4) and its receptors in fibroblast-myofibroblast transition and fibrotic failure of arteriovenous fistulas (AVFs)

BACKGROUND

Over 60% of End Stage Renal Disease (ESRD) patients are relying on hemodialysis (HD) to survive, and the arteriovenous fistula (AVF) is the preferred vascular access method for HD. However approximately half of all newly created AVF fail to mature and cannot be used without a salvage procedure. We have recently demonstrated an association between AVF maturation failure and post-operative fibrosis, while our RNA-seq study also revealed that veins that ultimately failed during AVF maturation had elevated levels of platelet factor 4 (PF4/CXCL4). However, a link between these two findings was yet to be established.

METHODS

In this study, we investigated potential mechanisms between PF4 levels and fibrotic remodeling in veins. We compared the local expression of PF4 and fibrosis marker integrin β6 (ITGB6) in veins that successfully underwent maturation with that in veins that ultimately failed to mature. We also measured the changes of expression level of α-smooth muscle actin (αSMA/ACTA2) and collagen (Col1/COL1A1) in venous fibroblasts upon various treatments, such as PF4 pharmacological treatment, alteration of PF4 expression, and blocking of PF4 receptors.

RESULTS

We found that PF4 is expressed in veins and co-localizes with αSMA. In venous fibroblasts, PF4 stimulates expression of αSMA and Col1 via different pathways. The former requires integrins αvβ5 and α5β1, while chemokine receptor CXCR3 is needed for the latter. Interestingly, we also discovered that the expression of PF4 is associated with that of ITGB6, the β subunit of integrin αvβ6. This integrin is critical for the activation of the major fibrosis factor TGFβ, and overexpression of PF4 promotes activation of the TGFβ pathway.

CONCLUSIONS

These results indicate that upregulation of PF4 may cause venous fibrosis both directly by stimulating fibroblast differentiation and expression of extracellular matrix (ECM) molecules and indirectly by facilitating the activation of the TGFβ pathway.

Inhibition of β-catenin signaling attenuates arteriovenous fistula thickening in mice by suppressing myofibroblasts

Background

Arteriovenous fistula (AVF) is the most important vascular access for hemodialysis; however, preventive treatment to maintain the patency of AVFs has not been developed. In endothelium, β-catenin functions in both the intercellular adherens complex and signaling pathways that induce the transition of endothelial cells to myofibroblasts in response to mechanical stimuli. We hypothesize that mechanical disturbances in the AVF activate β-catenin signaling leading to the transition of endothelial cells to myofibroblasts, which cause AVF thickening. The present study aimed to test this hypothesis.

Methods

Chronic kidney disease in mice was induced by a 0.2% adenine diet. AVFs were created by aortocaval puncture. Human umbilical vein endothelial cells (HUVECs) were used in the cell experiments. A pressure-culture system was used to simulate mechanical disturbances of the AVF.

Results

Co-expression of CD31 and smooth muscle alpha-actin (αSMA), loss of cell–cell adhesions, and the expression of the myofibroblast marker, integrin subunit β6 (ITGB6), indicated transition to myofibroblasts in mouse AVF. Nuclear translocation of β-catenin, decreased axin2, and increased c-myc expression were also observed in the AVF, indicating activated β-catenin signaling. To confirm that β-catenin signaling contributes to AVF lesions, β-catenin signaling was inhibited with pyrvinium pamoate; β-catenin inhibition significantly attenuated AVF thickening and decreased myofibroblasts. In HUVECs, barometric pressure-induced nuclear localization of β-catenin and increased expression of the myofibroblast markers, αSMA and ITGB6. These changes were attenuated via pretreatment with β-catenin inhibition.

Conclusions

The results of this study indicate that mechanical disturbance in AVF activates β-catenin signaling to induce the transition of endothelial cells to myofibroblasts. This signaling cascade can be targeted to maintain AVF patency.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00436-1.