Conditional knockout of AMP-activated protein kinase α2 allele leads to retinal cone photoreceptor degeneration

Abstract

Purpose: AMP-activated protein kinase (AMPK) acts as an energy sensor to maintain energy homeostasis at the cellular level. It functions as a heterotrimeric protein which consists of one catalytic subunit (α1 or α2), one regulatory subunit (β1 or β2) and one AMP-binding subunits (γ1, γ2, or γ3). Each of these subunits has a specific role in regulating the activity and stability or localization of AMPK. Activation of the AMPK pathway has been demonstrated to be neuroprotective in both light damage and inherited retinal degeneration models. The goal of this study was to determine whether deletion of one of the catalytic subunits AMPK α2 allele in the retina will affect normal retinal function and morphology.

Methods: Chx10 cre: AMPK α2^f/f mice are deficient of AMPK α2 in all retinal neurons and Müller glial cells. Retinal function was measured by electroretinography (ERG) and retinal structure was observed by Spectral domain Optical Coherence Tomography (SD-OCT). Western blots and real time PCR were used to study opsin protein and mRNA levels. Immunohistochemistry was used to identify the number of cone photoreceptors. All procedures with animals were conducted in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.

Results: Conditional knockout of AMPK α2 mice have normal retinal structure, thickness and scotopic ERG a-wave amplitudes. However, they have decreased photopic and flicker ERG responses starting at 2 months, which indicates cone photoreceptor degeneration. Immunohistochemistry using anti-M cone and S cone antibodies indicated a reduction in cone cell numbers at 6 months of age relative to control cre negative mice.

Conclusions: Our data suggest that conditional knockout of AMPK α2 leads to retinal cone photoreceptor degeneration. The data show that AMPK α2 has a unique role in cones, and that the AMPK pathway is essential for cone function and survival. The study further suggests that drugs designed to activate this pathway may have therapeutic benefit for macular degenerative diseases.