Loss of βA3/A1-crystallin in astrocytes lead to persistent fetal vasculature (PFV) by activating EGFR/mTORC1 signaling and inhibiting autophagy

Abstract

Purpose : Persistent fetal vasculature (PFV) is a human disease that results from failure of the fetal vasculature to regress normally. Nuc1 is a spontaneous mutation in the Cryba1 gene (encoding βA3/A1-crystallin). We have previously shown that in Nuc1 rats, normal regression of the hyaloid artery is inhibited and astrocytes abnormally ensheath the retained artery. Moreover, the Nuc1 astrocytes show atypical migration and increased proliferation, compared to controls. In this study we have investigated the molecular mechanisms that control proliferation and migration of astrocytes in Nuc1 rats.

Methods : Astrocytes were isolated and expanded in culture from the optic nerve of Nuc1 and wild type (WT) rats. MTS and wound healing assays were performed to investigate proliferation and migration respectively. Western blotting and immunostaining were used to study epidermal growth factor receptor (EGFR)/ mammalian target of rapamycin, complex 1 (mTORC1) signaling in astrocytes. The rate of autophagosome formation and degradation was investigated by transiently transfecting astrocytes with a tandem fluorescently tagged LC3 (RFP-GFP-LC3).

Results : We found that loss of βA3/A1-crystallin leads to aggregation of astrocytes in Nuc1 retina. Cultured Nuc1 astrocytes proliferate and migrate faster than WT. EGFR/mTORC1 signaling pathway and positive regulators of cell cycle are upregulated in Nuc1 astrocytes. Moreover, inhibition of mTORC1 and EGFR by AZD8055 and Gefitinib, respectively, lead to blockage of proliferation and migration of astrocytes in vitro. Activation of mTORC1 inhibits autophagy in Nuc1 astrocytes. Furthermore, we found that the lysosomal-mediated clearance of autolysosomes and EGFR in Nuc1 is reduced compared to WT astrocytes.

Conclusions : Our studies provide evidence that loss of βA3/A1-crystallin lead to abnormal proliferation and migration of astrocytes. Furthermore, impaired lysosomal function in Nuc1 astrocytes activates EGFR/mTORC1 signaling, exacerbating abnormal proliferation and migration. Our data suggests that inhibition of the EGFR/mTORC1 pathway may help to develop therapy for PFV, a blinding childhood disease with limited treatment options at present.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.