New functions of Müller cells

Abstract

Müller cells, the major type of glial cells in the retina, are responsible for the homeostatic and metabolic support of retinal neurons. By mediating transcellular ion, water, and bicarbonate transport, Müller cells control the composition of the extracellular space fluid. Müller cells provide trophic and anti-oxidative support of photoreceptors and neurons and regulate the tightness of the blood-retinal barrier. By the uptake of glutamate, Müller cells are more directly involved in the regulation of the synaptic activity in the inner retina. This review gives a survey of recently discoved new functions of Müller cells. Müller cells are living optical fibers that guide light through the inner retinal tissue. Thereby they enhance the signal/noise ratio by minimizing intraretinal light scattering and conserve the spatial distribution of light patterns in the propagating image. Müller cells act as soft, compliant embedding for neurons, protecting them in case of mechanical trauma, and also as soft substrate required for neurite growth and neuronal plasticity. Müller cells release neuroactive signaling molecules which modulate neuronal activity, are implicated in the mediation of neurovascular coupling, and mediate the homeostasis of the extracellular space volume under hypoosmotic conditions which are a characteristic of intense neuronal activity. Under pathological conditions, a subset of Müller cells may differentiate to neural progenitor/stem cells which regenerate lost photoreceptors and neurons. Increasing knowledge of Müller cell function and responses in the normal and diseased retina will have great impact for the development of new therapeutic approaches for retinal diseases.

Elevated cell proliferation and VEGF production by high-glucose conditions in Müller cells involve XIAP

“…[6][7][8] Reactive gliosis including hypertrophy, enlargement of soma, and proliferation are the most obvious pathological changes that occur in Mü ller cells during diabetes. 9,10 Moreover, increased VEGF expression in Mü ller cells under hyperglycemic conditions is one of the major contributors to pathological intraocular neovascularization.…”

Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision

“…This 'inverted' retinal structure is expected to cause blurring of the image and reduction in the photon flux reaching the photoreceptors, thus reducing their sensitivity [6][7][8][9] . It has been recently reported that retinal Müller cells act as light guides serving to transfer light across the retina, from the vitreo-retinal border towards the photoreceptors [10][11][12] . However, the basic question remains: How does light propagation via Müller cells through the neuronal layers of the retina affect vision?…”

Gap Junction Coupled Cells, Barriers and Systemic Inflammation

“…Both astrocytes and Müller cells in the retina cover the blood vessels with their endfeet forming the BRB [30]. The Müller cells are specialized radial glial cells and span through the entire thickness of the retina.…”