Vertebrate photoreceptors are among the most metabolically active cells, exhibiting a high rate of ATP consumption. This is coupled with a high anabolic demand, necessitated by the diurnal turnover of a specialized membrane-rich organelle, the outer segment, which is the primary site of phototransduction. How photoreceptors balance their catabolic and anabolic demands is poorly understood. Here, we show that rod photoreceptors in mice rely on glycolysis for their outer segment biogenesis. Genetic perturbations targeting allostery or key regulatory nodes in the glycolytic pathway impacted the size of the outer segments. Fibroblast growth factor signaling was found to regulate glycolysis, with antagonism of this pathway resulting in anabolic deficits. These data demonstrate the cell autonomous role of the glycolytic pathway in outer segment maintenance and provide evidence that aerobic glycolysis is part of a metabolic program that supports the biosynthetic needs of a normal neuronal cell type.

The aim of this study was to identify the mechanisms by which angiotensin II alters the physiology of the pericyte‐containing microvasculature of the retina. Despite evidence that this vasoactive signal regulates capillary perfusion by inducing abluminal pericytes to contract and thereby microvascular lumens to constrict, little is known about the events linking angiotensin exposure with pericyte contraction. Here, using microvessels freshly isolated from the adult rat retina, we monitored pericyte currents via perforated‐patch pipettes, measured pericyte calcium levels with fura‐2 and visualized pericyte contractions and lumen constrictions by time‐lapse photography. We found that angiotensin activates nonspecific cation (NSC) and calcium‐activated chloride channels; the opening of these channels induces a depolarization that is sufficient to activate the voltage‐dependent calcium channels (VDCCs) expressed in the retinal microvasculature. Associated with these changes in ion channel activity, intracellular calcium levels rise, pericytes contract and microvascular lumens narrow. Our experiments revealed that an influx of calcium through the NSC channels is an essential step linking the activation of AT₁ angiotensin receptors with pericyte contraction. Although not required in order for angiotensin to induce pericytes to contract, calcium entry via VDCCs serves to enhance the contractile response of these cells. In addition to activating nonspecific cation, calcium‐activated chloride and voltage‐dependent calcium channels, angiotensin II also causes the functional uncoupling of pericytes from their microvascular neighbours. This inhibition of gap junction‐mediated intercellular communication suggests a previously unappreciated complexity in the spatiotemporal dynamics of the microvascular response to angiotensin II.

The aim of this study was to test the hypothesis that the neurotransmitter acetylcholine regulates the function of pericyte-containing retinal microvessels. A vasoactive role for acetylcholine is suggested by the presence of muscarinic receptors on pericytes, which are abluminally positioned contractile cells that may regulate capillary perfusion. However, little is known about the response of retinal microvessels to this neurotransmitter. Here we assessed the effects of cholinergic agonists on microvessels freshly isolated from the adult rat retina. Ionic currents were monitored via perforated patch pipettes; intracellular Ca²⁺levels were quantified with the use of fura 2, and microvascular contractions were visualized with the aid of time-lapse photography. We found that activation of muscarinic receptors elevated pericyte calcium levels, increased depolarizing Ca²⁺-activated chloride currents and caused pericytes to contract in a Ca²⁺-dependent manner. Most contracting pericytes were near capillary bifurcations. Contraction of a pericyte caused the adjacent capillary lumen to constrict. Thus acetylcholine may serve as a vasoactive signal by regulating pericyte contractility and thereby capillary perfusion in the retina.

Nrf2, a transcription factor that regulates the response to oxidative stress, has been shown to rescue cone photoreceptors and slow vision loss in mouse models of retinal degeneration (rd). The retinal pigment epithelium (RPE) is damaged in these models, but whether it also could be rescued by Nrf2 has not been previously examined. We used an adeno-associated virus (AAV) with an RPE-specific (Best1) promoter to overexpress Nrf2 in the RPE of rd mice. Control rd mice showed disruption of the regular array of the RPE, as well as loss of RPE cells. Cones were lost in circumscribed regions within the cone photoreceptor layer. Overexpression of Nrf2 specifically in the RPE was sufficient to rescue the RPE, as well as the disruptions in the cone photoreceptor layer. Electron microscopy showed compromised apical microvilli in control rd mice but showed preserved microvilli in Best1-Nrf2–treated mice. The rd mice treated with Best1-Nrf2 had slightly better visual acuity. Transcriptome profiling showed that Nrf2 upregulates multiple oxidative defense pathways, reversing declines seen in the glutathione pathway in control rd mice. In summary, Nrf2 overexpression in the RPE preserves RPE morphology and survival in rd mice, and it is a potential therapeutic for diseases involving RPE degeneration, including age-related macular degeneration (AMD).