Integrin β3 Induction Promotes Tubular Cell Senescence and Kidney Fibrosis

Tubular cell senescence is a common biologic process and contributes to the progression of chronic kidney disease (CKD); however, the molecular mechanisms regulating tubular cell senescence are poorly understood. Here, we report that integrin β3 (ITGB3) expression was increased in tubular cells and positively correlated with fibrosis degree in CKD patients. ITGB3 overexpression could induce p53 pathway activation and the secretion of TGF-β, which, in turn, resulted in senescent and profibrotic phenotype change in cultured tubular cells. Moreover, according to the CMAP database, we identified isoliquiritigenin (ISL) as an agent to inhibit ITGB3. ISL treatment could suppress Itgb3 expression, attenuate cellular senescence, and prevent renal fibrosis in mice. These results reveal a crucial role for integrin signaling in cellular senescence, potentially identifying a new therapeutic direction for kidney fibrosis.

Serotonin transporter-mediated molecular axis regulates regional retinal ganglion cell vulnerability and axon regeneration after nerve injury

Molecular insights into the selective vulnerability of retinal ganglion cells (RGCs) in optic neuropathies and after ocular trauma can lead to the development of novel therapeutic strategies aimed at preserving RGCs. However, little is known about what molecular contexts determine RGC susceptibility. In this study, we show the molecular mechanisms underlying the regional differential vulnerability of RGCs after optic nerve injury. We identified RGCs in the mouse peripheral ventrotemporal (VT) retina as the earliest population of RGCs susceptible to optic nerve injury. Mechanistically, the serotonin transporter (SERT) is upregulated on VT axons after injury. Utilizing SERT-deficient mice, loss of SERT attenuated VT RGC death and led to robust retinal axon regeneration. Integrin β3, a factor mediating SERT-induced functions in other systems, is also upregulated in RGCs and axons after injury, and loss of integrin β3 led to VT RGC protection and axon regeneration. Finally, RNA sequencing analyses revealed that loss of SERT significantly altered molecular signatures in the VT retina after optic nerve injury, including expression of the transmembrane protein, Gpnmb. GPNMB is rapidly downregulated in wild-type, but not SERT- or integrin β3-deficient VT RGCs after injury, and maintaining expression of GPNMB in RGCs via AAV2 viruses even after injury promoted VT RGC survival and axon regeneration. Taken together, our findings demonstrate that the SERT-integrin β3-GPNMB molecular axis mediates selective RGC vulnerability and axon regeneration after optic nerve injury.

Bone Morphogenetic Protein 2 Increases Human Trophoblast Invasion by Up-Regulating Integrin Beta3

The adequate invasion of extravillous trophoblast cells (EVTs) is indispensable for the implantation of embryos and subsequent remodeling of uterine spiral arteries in early human gestation. Bone morphogenetic protein 2 (BMP2), which is abundantly expressed at the maternal-fetal interface, has been shown to promote the human EVT invasion process (1). Integrin switching (i.e., a switch from α6β4 to αvβ3) plays essential roles in cell-extracellular matrix adhesion and has been reported to influence EVT migration and invasion (2). Moreover, integrin β3 has been found to promote the adhesion, invasion, and migration abilities of embryonic trophoblasts (3). However, whether integrin β3 participates in BMP2 signaling and mediates BMP2-increased-human trophoblast invasion remains unknown. The purpose of our study was to explore the effects of BMP2 on integrin αvβ3 expression and the possible mediation role of integrin β3 in BMP2-regulated human trophoblast invasion. We used immortalized human trophoblast cell line (HTR8/SVneo) and primary human extravillous trophoblast cells (EVTs) isolated from first-trimester villi as study models. RT-qPCR and Western blot assay were respectively utilized to detect the messenger RNA and protein levels of intergrin αv and β3. The function of the target protein was studied by siRNA knockdown, and the trophoblast invasion ability was checked by Matrigel-coated transwell invasion assays. Our results demonstrated that the mRNA and protein levels of integrin β3, rather than integrin αv, were up-regulated after BMP2 treatment in HTR8/SVneo and primary EVT cells. Importantly, siRNA-mediated down-regulation of integrin β3 significantly inhibited basal and BMP2-induced HTR8/SVneo cell invasionas measured by transwell invasion assay. In conclusion, we findings support that BMP2 promotes human trophoblast cell invasion by up-regulating integrin β3 expression, benefiting the in-depth understanding of the pro-invasive effect of BMP2 on human trophoblasts during early pregnancy. Reference: (1) Hong-Jin Zhao et al., Cell Death Dis 2018;9:174. (2) Damsky, C.H. et al, Development 1994; 120, 3657-3666. (3) Dong-Mei He et al., Reproduction 2019;157:423-430.

Substrate Stiffness and Stretch Regulate Profibrotic Mechanosignaling in Pulmonary Arterial Adventitial Fibroblasts

Pulmonary arterial adventitial fibroblasts (PAAFs) are important regulators of fibrotic vascular remodeling during the progression of pulmonary arterial hypertension (PAH), a disease that currently has no effective anti-fibrotic treatments. We conducted in-vitro experiments in PAAFs cultured on hydrogels attached to custom-made equibiaxial stretchers at 10% stretch and substrate stiffnesses representing the mechanical conditions of mild and severe stages of PAH. The expression of collagens α(1)I and α(1)III and elastin messenger RNAs (Col1a1, Col3a1, Eln) were upregulated by increased stretch and substrate stiffness, while lysyl oxidase-like 1 and α-smooth muscle actin messenger RNAs (Loxl1, Acta2) were only significantly upregulated when the cells were grown on matrices with an elevated stiffness representative of mild PAH but not on a stiffness representative of severe PAH. Fibronectin messenger RNA (Fn1) levels were significantly induced by increased substrate stiffness and transiently upregulated by stretch at 4 h, but was not significantly altered by stretch at 24 h. We modified our published computational network model of the signaling pathways that regulate profibrotic gene expression in PAAFs to allow for differential regulation of mechanically-sensitive nodes by stretch and stiffness. When the model was modified so that stiffness activated integrin β3, the Macrophage Stimulating 1 or 2 (MST1\2) kinases, angiotensin II (Ang II), transforming growth factor-β (TGF-β), and syndecan-4, and stretch-regulated integrin β3, MST1\2, Ang II, and the transient receptor potential (TRP) channel, the model correctly predicted the upregulation of all six genes by increased stiffness and the observed responses to stretch in five out of six genes, although it could not replicate the non-monotonic effects of stiffness on Loxl1 and Acta2 expression. Blocking Ang II Receptor Type 1 (AT1R) with losartan in-vitro uncovered an interaction between the effects of stretch and stiffness and angiotensin-independent activation of Fn1 expression by stretch in PAAFs grown on 3-kPa matrices. This novel combination of in-vitro and in-silico models of PAAF profibrotic cell signaling in response to altered mechanical conditions may help identify regulators of vascular adventitial remodeling due to changes in stretch and matrix stiffness that occur during the progression of PAH in-vivo.

Circulating Exosomal Integrin β3 Is Associated with Intracranial Failure and Survival in Lung Cancer Patients Receiving Cranial Irradiation for Brain Metastases: A Prospective Observational Study

Brain metastasis (BM) is a major problem in patients with cancer. Exosomes or extracellular vesicles (EV) and integrins contribute to the development of BM, and exosomal integrins have been shown to determine organotropic metastasis. We hypothesized that circulating EV integrins are able to influence the failure patterns and outcomes in patients treated for BM. We prospectively enrolled 75 lung cancer patients with BM who received whole brain radiotherapy (WBRT). We isolated and quantified their circulating EV integrins, and analyzed the association of EV integrins with clinical factors, survival, and intracranial/extracranial failure. Circulating EV integrin levels were independent of age, sex, histology, number of BM, or graded prognostic assessment score. Age, histology, and graded prognostic assessment score correlated with survival. Patients with higher levels of circulating EV integrin β3 had worse overall survival (hazard ratio: 1.15 per 1 ng/mL increase; p = 0.04) following WBRT. Multivariate regression analysis also showed a higher cumulative incidence of intracranial failure (subdistribution hazard ratio: 1.216 per 1 ng/mL increase; p = 0.037). In conclusion, circulating EV integrin β3 levels correlated with survival and intracranial control of patients with lung cancer after WBRT for BM. This supports that EV integrin β3 mediates a brain-tropic metastasis pattern, and may serve as a novel prognostic biomarker for BM.

Integrin β3 Targeting Biomaterial Preferentially Promotes Secretion of bFGF and Proliferation of iPSC-Derived Vascular Smooth Muscle Cells

Human-induced pluripotent stem cell-derived-vascular smooth muscle cells (hiPSC-VSMC) have been shown to promote angiogenesis and wound healing. However, there is a paucity of research on how the extracellular matrix (ECM) microenvironment may impact the hiPSC-VSMC’s function. In this study, our objective was to understand the effect of specific ECM ligand-integrin interaction on hiPSC- VSMC’s paracrine secretion, cell proliferation, and morphology. We here showed a precise modulation of hiPSC-VSMC in a fibronectin functionalized fibrillar collagen scaffold by targeting their integrin β3. The secretion of proangiogenic growth factor, basic fibroblast growth factor (bFGF) was found to be fibronectin dependent via αvβ3 integrin interactions. Also, our data indicate the possible role of a positive feedback loop between integrin β3, bFGF, and matrix metalloproteinase-2 in regulating hiPSC- VSMC’s morphology and cell proliferation. Finally, the secretome with improved proangiogenic activity shows potential for future regenerative applications.