Stretch strain shifts optic nerve head astrocyte metabolism to enrich α-ketoglutarate and the pentose phosphate pathway

Optic nerve head (ONH) astrocyte deformation contributes to glaucoma pathology by increasing extracellular matrix (ECM) deposition which promotes fibrosis in the ONH. To investigate how fibrosis and effector Yes-associated protein (YAP) activation is linked to metabolism, we examined YAP and alteration of tricarboxylic acid (TCA) cycle intermediates. Rat ONH astrocytes were subjected to biaxial stretch at 1 Hz for 24 h while cultured on various substrates. Stretched ONH astrocytes provided with uniformly-labeled 13C glucose ([U-13C6]glucose) for 2 h yielded TCA cycle metabolites identified using GC-MS. Nuclear YAP translocation, glucose transporter 1 (GLUT1), and the laminin receptor Integrin β4 were significantly increased when ONH astrocytes exposed to stretch strain were cultured on laminin. Global disruption of TCA cycle intermediates occurred in the stretched ONH astrocytes, with reductions of citrate, pyruvate, lactate and glutamine. Significantly elevated α-ketoglutarate (α-KG) derived from [U-13C6]glucose was observed in the stretched ONH astrocytes, concomitant with increased histone demethylation. Increases in specific isotopologues of α-KG derived [2,3-13C2]glucose as well as increased pentose phosphate pathway (PPP) enzymes, with decreased pyruvate and lactate, support shunting of glucose-6-phosphate into the PPP. Our findings suggest YAP is an important integrator of ECM changes that contributes to metabolic reprogramming in ONH astrocytes under glaucoma-associated stress.