Angiotensin Converting Enzyme 2 (ACE2) Expression in the Aged Brain and Visual System.

Area of Science:

• Ophthalmology
• Neuroscience
• Virology

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) utilizes the angiotensin-converting enzyme 2 (ACE2) receptor for host cell entry.
• ACE2 receptors are expressed across various cell types, including neural and non-immune cells, enabling SARS-CoV-2 to infect multiple tissues.
• Previous research indicated ACE2 expression in the eye and visual brain circuitry, hinting at potential ocular and neurological involvement in COVID-19.

Purpose of the Study:

• To investigate the expression of ACE2 receptors in various cell types within the human visual system.
• To determine if ocular and neural cells involved in vision possess the necessary receptors for SARS-CoV-2 invasion.
• To explore the potential pathway of SARS-CoV-2 entry into the brain via the visual system.

Main Methods:

• Analysis of ACE2 receptor expression at both mRNA and protein levels.
• Examination of ocular tissues, including the external eye.
• Investigation of deep brain regions associated with visual signal processing.

Main Results:

• ACE2 receptors are present in numerous cell types of the human visual system, including ocular and neural cells.
• Widespread ACE2 expression was confirmed in the eye and brain regions responsible for visual processing.
• A gradient of increasing ACE2 expression was observed from the anterior eye surface towards the occipital lobe and visual cortex.

Conclusions:

• The human visual system, encompassing the eye and visual processing centers in the brain, expresses ACE2 receptors, making it susceptible to SARS-CoV-2 infection.
• The identified gradient of ACE2 expression suggests a potential route for SARS-CoV-2 to infiltrate the brain through the visual pathway.
• These findings may contribute to understanding the neuro-ophthalmic manifestations observed in COVID-19 patients.