Case Study: Assessment of CPCB-RPE1 Retinal Patch in a Postmortem Patient Two Years Post-Implantation

Article: Stem cell-derived retinal patch is shown to survive two years post-implantation
Source: University of California, Santa Barbara
Published: March 15, 2022

CPCB-RPE1 retinal patch in implanted eye 1 year post-op (upper right)

One area of research in the treatment of degenerative diseases of the retina, such as age-related macular degeneration (AMD), is through stem cells. These stem cells are delivered through subretinal injection or through the implantation of a patch of cells beneath the retina. Researchers at UCSB report a follow-up for the California Project to Cure Blindness – Retinal Pigment Epithelium 1 (CPCB-RPE1) patch, which has been in development since 2013 and consists of a monolayer of human stem cell-derived RPE cells cultured on an ultrathin membrane of biologically inert parylene. Early results of Phase 1 clinical trials were encouraging. Of the 15 patients in the initial cohort, four showed visual improvement and five experienced stabilization of their vision. More recently, one of the patients, named "Subject 125," passed away from pneumonia, allowing the researchers the opportunity to study her donated eyes postmortem and check the progress of their patch. Staining and immunoreactivity testing confirmed that the cells were donor RPE cells and that they were well-oriented in a polarized position (like in a natural retina). Furthermore, retinal histology revealed phagocytic activity, demonstrating that the RPE stem cells were functional in their role of recycling photoreceptor outer segment discs. Importantly, after two years, the presence of the patch did not trigger signs of rejection, such as inflammation, neovascularization, or scarring, even without immunosuppressants (which were stopped two months after implantation). The research team are working on Phase 2 of the clinical trials to test the patch's effectiveness, as well as developing advances to extend the patch's shelf life through cryopreservation and composite implants that combine multiple retinal cell types to treat various stages of retinal disease.

Retinal histopathology shows active RPE implant cells by presence of RPE65 (green) (B). Donor RPE cells express Na+/K+-ATPase (red) in a largely apical distribution consistent with mature and functional RPE (C). Donor RPE of the implant suggests presence of phagosomes containing photoreceptor outer segments; yellow immunofluorescence represents red-stained phagosomes (rhodopsin) in green-stained cytoplasm (RPE65) (G).

My rating of this study: ⭐⭐

Kashani AH, Lebkowski JS, Hinton DR, et al. "Survival of an HLA-mismatched, bioengineered RPE implant in dry age-related macular degeneration." Stem Cell Reports. 17(3):P448-458. 8 March 2022.
https://doi.org/10.1016/j.stemcr.2022.01.001

Spatio-Temporal FD-FF-OCT for Imaging of the Choroid

Article: OCT studies without noise. A new method for better detection of eye diseases. 
Source: Polish Academy of Sciences (Poland)
Published: March 14, 2022

En face imaging of the choroid using FD-FF-OCT with multimode fiber

The advent of optical coherence tomography (OCT), a noninvasive, quick, and accessible imaging modality, was a major advancement in easy detection and monitoring of ocular pathology, such as those that affect the retina, optic nerve, and cornea. Similar to technology such as ultrasound, but which uses light instead of sound, in this case, near-infrared light, OCT produces high-resolution 3-dimensional images, called tomograms, or 2-dimensional images in cross-section or en face. Engineers continue to make strides in improving this technology from the initial time domain OCTs to the more recent frequency domain OCTs (e.g., swept source and spectral domain OCTs), also called Fourier domain OCTs due to the mathematical theorem that the detector uses to correlate time with different light wavelengths. Researchers in Poland are exploring the use of multimode optical fibers to reduce background noise (speckle or cross-talk) in Fourier domain OCT. Unlike classical OCTs, which use partially coherent light (coherence in time but not space), the newly developed spatio-temporal optical coherence tomography (STOC-T) is the first OCT model that combines the properties of coherence interferometry in both time and space. The reduction in image speckle is especially suitable for imaging the choroid, which provides the blood supply to most of the eyeball and is the most posterior tissue that OCT technology assesses. The challenge of imaging at increased depth (with exceptional contrast) is explored by the researchers using multimode optical fibers. A press release explains, "Until now, such devices have been used repeatedly to transmit data, but no one considered the fact that each of the spatial patterns come out of the several hundred meters of such optical fiber at different times. This time-dependence results in several hundred OCT images being captured during a single measurement; when added together the composite pattern reduces unwanted effects such as speckle noise in totally passive way." Using FD-FF-OCT with the multimode optical fibers (300m length), the researchers were able to produce "noiseless" images of the choroid to the choroidal-scleral junction and high-contrast en face images of the choroid. Limitations to the technology at this point are restricted axial range and substantial data processing.

My rating of this study: ⭐⭐⭐⭐

Auksorius E, Borycki D, Wegrzyn P, et al. "Multimode fiber as a tool to reduce cross talk in Fourier-domain full-field optical coherence tomography." Optics Letters.  47(4):838-841. 2022.   https://doi.org/10.1364/OL.449498

Associations Between Retinal Layers and the Brain

Article: The Retina as a Possible Biomarker for Reduced Brain Matter
Source: University of Bonn (Germany)
Published: March 16, 2022
Article: The Retina as a Possible Biomarker for Reduced Brain Matter
Source: German Center for Neurodegenerative Diseases (Germany)
Published: March 15, 2022

SD-OCT of the retina

The retina is an extension of the brain and as such shares many neurological characteristics of brain matter. Researchers in Germany further explored the similarities between the two tissues as a means of using retinal imaging to assess potential biomarkers of brain atrophy. Called the Rhineland Study, this study involved almost 2,872 subjects who participated in retinal scans via spectral domain optical coherence tomography (SD-OCT) and brain scans via magnetic resonance imaging (MRI). Compared to techniques used in earlier studies, SD-OCT is a newer retinal imaging technology and allowed for more detailed imaging of all the retinal layers. The researchers then used computer software to compare the thickness and volume of the various retinal layers with the thickness and volume of brain structures. They found a close positive association between the volume (and microstructural integrity, as assessed by fractional anisotropy) of the inner retinal layers and the so-called white matter of the brain. By contrast, the outer retinal layers were associated with the brain's gray matter. These associations were particularly pronounced in the occipital lobe, where visual processing takes place, and, interestingly, also with volume of the hippocampus where memory is formed and is an area often affected in dementia. Because retinal scans are noninvasive, quick, and relatively accessible, they could be an easy method to detect and monitor brain atrophy and the progression of neurological degenerative diseases. The researchers next plan to expand their studies to larger patient groups and over longer periods to verify the results in clinical settings.

My rating of this study: ⭐⭐

Mauschitz MM, Lohner V, Koch A, et al. "Retinal layer assessments as potential biomarkers for brain atrophy in the Rhineland Study." Scientific Reports.  12:2757. 17 February 2022. https://doi.org/10.1038/s41598-022-06821-4 

Hybrid Müller Glia and Adult Stem Cells "Awaken" Potential for Mammalian Retinal Regeneration

Article: Cell fusion ‘awakens’ regenerative potential of human retina
Source: Centre for Genomic Regulation (Spain)
Published: March 15, 2022

Immunostaining of human retinal organoids microinjected with hybrids.
Cell fusion is enhanced by activation of the Wnt/beta-catenin pathway (top).  

Müller glia are support cells in the retina where they perform a variety of functions, from channeling light to mitigating cellular stress. The Müller glia of lower vertebrates, such as salamanders and fish, have the capacity to regenerate neural tissue—that is, engage in mitosis—in response to retinal damage; however, this capacity is lost in mammalian retinas and visual impairment due to retinal damage is permanent. Researchers in Spain wanted to explore the regenerative potential of these glial cells combined with stem cells as a therapeutic opportunity in humans, noting that cell fusion events, although rare, also occur in human tissues of the liver, brain, and gastrointestinal tract. In the study, the team of scientists conducted in vitro fusion of Müller glia and cells derived from adult human mesenchymal and hematopoietic stem and progenitor cells (adipose and bone marrow stem cells). The resulting hybrid cells were then injected into a retinal organoid model, where they were observed to successfully engraft into the tissue and differentiate into cells that closely resemble retinal ganglion cells. The authors write, importantly, "cell fusion efficiency is enhanced by inflammatory signals [from the retina] and that the activation of the Wnt/beta-catenin pathway increases differentiation of the hybrids into neuronal-like cells." The findings show that Müller glia retain regenerative activity, and that hybrids between Müller glia and adult stem cells might be a promising stem cell-mediated therapy for human retina regeneration that could be used to treat visual impairment. The researchers next plan to investigate why the hybrid cells, with four complete sets of chromosomes, do not result in chromosomal instability or cancer development; they hypothesize that cells of the retina have a mechanism that acts as a genetic reservoir (similar to those found in the human liver) to regulate chromosome segregation. 

My rating of this study: ⭐⭐

Bonilla-Pons SA, Nakagawa S, Bahima EG, et al. "Müller glia fused with adult stem cells undergo neural differentiation in human retinal models." eBioMedicine.  77:103914. 1 March 2022. https://doi.org/10.1016/j.ebiom.2022.103914 

Regenerative Treatment of Diabetic Retinal Microvascular Pathology Using Stem Cells

Article: Study shows human induced pluripotent stem cells improve visual acuity, vascular health
Source: Indiana University School of Medicine
Published: March 10, 2022

Vascular density assessment in retinas of diabetic mice injected with
either saline or KNA cells. All parameters indicate a restoration
of retinal vascularity with KNA cell treatment compared to saline
control injection. Notably, blood vessel growth was robust
without giving rise to teratomas.

According to the Center for Disease Control and Prevention, more than 37 million people in the U.S. have diabetes, with complications affecting the microvasculature of organs such as the kidneys and eyes and of peripheral nerves. A team of researchers conducted a multi-site study investigating the use of human induced pluripotent stem cells (hiPSCs) as a regenerative approach in the treatment of microvascular diseases, such as in diabetic retinopathy. In this pre-clinical study, investigators genetically reprogrammed diabetic and non-diabetic peripheral blood cells into hiPSCs and matured the cells into a specific mesoderm subset, KNA+ mesoderm, that had high clonal proliferative potential and specification into cells similar to endothelial colony forming cells (ECFC). These stem cells were delivered by intravitreal injection to mice with type 2 diabetic retinal dysfunction. Results showed that the ECFCs formed functional blood vessels in vivo, effectively increasing vascular density and perfusion to retinal tissue. Electroretinography and optokinetic nystagmus vision testing showed significant improvement in neural retinal response and visual acuity, respectively. They hypothesized that the hiPSC-derived vascular reparative cells may serve as a source of endothelial precursors. The authors report, "Transcriptomic analysis showed that differentiation of hiPSCs derived from diabetics into KNA+ cells was sufficient to change baseline differences in gene expression caused by the diabetic status and reprogram diabetic cells to a pattern similar to KNA+ cells derived from nondiabetic hiPSCs." That is, these findings show a pre-clinical proof-of-concept that KNA+ cells can be used to restore perfusion and correct vascular dysfunction.

My rating of this study: ⭐⭐⭐

Gil C, Chakraborty D, Vieira CP, et al. "Specific mesoderm subset derived from human pluripotent stem cells ameliorates microvascular pathology in type 2 diabetic mice." Science Advances.  8(9). 4 March 2022. https://www.science.org/doi/10.1126/sciadv.abm5559

Intracrine Activity in Meibomian Gland Dysfunction and Treatment with NAD Precursor, in Mice

Article: Mutant mice shed no tears
Source: Kyoto University (Japan)
Published: March 10, 2022

The most common cause of dry eyes is age-associated dysfunction of the meibomian glands, which are glands in the eyelids and produce the lipid layer of the tear film that prevents tear evaporation. This age-related dysfunction is thought to be due to a decline of the sex steroid hormones testosterone and estrogen, produced by the enzyme 3-hydroxyl-steroid dehydrogenase (3-HSD). Though the sex steroid hormones are classically associated with the endocrine organs, and travel throughout the body through the bloodstream, a new study by researchers in Japan using a genetically modified mouse model indicate that the meibomian glands depend on a more recently discovered intracrine system in which the hormone acts in the tissue where it is synthesized. Lead author of the study states, "Indeed, disturbed intracrine 3-HSD enzyme activity in mutant mice was found to result in atrophy of the gland, which further led to the disorder." The enzyme 3-HSD is of particular interest for its circadian activity, which regulates behaviors such as sleep, menstrual cycles, and hormone secretion. In the meibomian glands, 3-HSD is regulated by cofactor nicotinamide adenine dinucleotide (NAD), a coenzyme found in every cell and also sold as an over-the-counter supplement. When nicotinamide mononucleotide (NMN), a NAD precursor, is administered topically to mice before sleep, when 3-HSD activity peaks, it elevated the amount of NAD needed to reboot 3-HSD activity. Periodic administration of NMN in mice 4 times nightly over 90 days reduced atrophy of the meibomian glands, thereby alleviating dryness of the eyes. The researchers emphasize NMN's benefits in not only being a local therapy, but also a non-steroidal agent, which avoids the adverse or unanticipated effects of hormones.

Mouse eyes treated with vehicle (left eye) and NAD precursor nicotinamide riboside or nicotinamide mononucleotide (right eye); arrows indicate areas of epithelial defect in eyes not treated with active agent 

My rating of this study: ⭐⭐

Sasaki L, Hamada Y, Yarimizu D, et al. "Intracrine activity involving NAD-dependent circadian steroidogenic activity governs age-associated meibomian gland dysfunction." Nature Aging.  2:105-114. 10 February 2022. https://doi.org/10.1038/s43587-021-00167-8 

White Sclera Enhances Eye Gaze Communication

Article: The language of the eyes
Source: University of Konstanz (Germany)
Published: March 8, 2022

A uniform white sclera in humans
enhances visibility of eye gaze direction

The sclera, the tough protective layer that provides structure to the shape of the eyeball, is white in humans. But this is not uniformly the case in animals, even among primates such as chimpanzees, humans' closest relatives. Researchers studying the significance of the sclera's color discovered that the white of the eye contributes decisively to the visibility of eye gaze direction through its basic color properties. In the experiments, humans and chimpanzees—the cross-species comparison enabling novel differentiation among competing hypotheses, the researchers note—were presented with images on a computer screen, varied in brightness and size of stimulus against varied background shading and distancing ("visually challenging conditions"), and tasked with distinguishing gaze direction for both groups. They found that both humans and chimpanzees distinguished eye-gaze directions of humans better than those of chimpanzees, especially in the visually challenging conditions. Furthermore, when the contrast polarity of the eyes of chimpanzees was reversed compared to what is normal, that is, showing a white sclera and a darker iris, both humans and chimpanzees were able to distinguish gaze direction of the chimpanzees better, indicating that uniform whiteness of the sclera facilitates the visibility of eye gaze direction even across species. Sometimes taken for granted in daily life, the ability to understand the language of the eyes is something we rely on in social activities and when interacting with one another face to face, where eye-gaze signaling is used for communication such as joint attention. First author of the study comments, "We owe this to the formation of the whites of the eye. Humans might have evolved this distinguishing eye feature for conspecific communication...In doing so, humans have probably evolved a unique communicative style critical for their hallmark social activities." 

Human and chimpanzee stimulus eyes in direct and averted (20°) gaze
in normal and reversed contrast polarities, varied in brightness and size

My rating of this study: ⭐

Kano F, Kawaguchi Y and Hanling Y. "Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees." eLife.  8 March 2022. https://doi.org/10.7554/eLife.74086 

Citrullination Bunker in Müller Glia Endfeet Preserves Sight in Early Stages of Retinal Stress

Article: Bunkers That Save Sight? Researchers Take a Close Look
Source: University of Connecticut
Published: March 8, 2022

Wet-AMD human retina (bottom) showing citrullination localized 
at Müller cell endfeet (M and N stained for a citrullination targeting
protein and its citrullinated form in green and red, respectively)
compared to control human retina (top)

Müller glia are support cells that axially span the retina from its inner surface (the inner limiting membrane) to the base of the photoreceptors. These support cells have properties that aid in mechanical strength and response to cellular stress (reactive gliosis) as well as channeling incoming light to the photoreceptors, where light is transduced to electrical signals to be sent to the brain. Scientists studying Müller glia in retinal laser injury, a genetically modified mouse model, and in human wet-AMD tissues recently discovered that the endfeet of these cells, specifically at the end opposite to the photoreceptors, also possess the ability to sequester cellular stress in the early stages of retinal degeneration before it affects the photoreceptors. At the endfeet of Müller cells, proteins become modified in a process called citrullination, in which the amino acid arginine is changed into citrulline, when the retina is under stress. The researchers hypothesize that this process is due in part to the difference in charge between arginine, which is positively charged, and citrulline, which is not, and that the loss of positive charge changes the mechanical properties of the cell such that it is less able to adapt to fluid build-up when the retina is under stress. Alternatively, it's possible that citrulline is seen as foreign to the body and triggers an autoimmune response. Citrullination can spread to affect the rest of the cell and neighboring cells, such as in later stages of disease, e.g., in age-related macular degeneration (AMD). However, this study emphasizes that the "bunkering" of citrullination in the Müller cells' endfeet, far from the photoreceptors, permits light detection to continue even as the retina responds to early stress. The team identified that the citrullination is controlled by the enzyme peptidyl arginine deiminase-4 (PAD4), and development of inhibitors of PAD4 could delay or prevent disease progression at early stages to preserve eyesight for longer.

My rating of this study: ⭐⭐⭐

Palko SI, Saba NJ, Mullane E, et al. "Compartmentalized citrullination in Muller glial endfeet during retinal degeneration." PNAS.  119(9):e2121875119. 23 February 2022. https://doi.org/10.1073/pnas.2121875119 

A Direct Circuit Between Auditory & Visual Cortices Explains Cross-Modal Memory Formation, Suppression

Article: Remembering Is Seeing
Source: Harvard Medical School
Published: March 8, 2022

Direct projections between the auditory cortex (AuC, red) 
and the primary visual cortex (V1, green)

Memory is traditionally thought of as being processed in higher-order regions of the brain. Yet, in the sensory areas of the brain, there is an undeniable interplay between both these higher-order cognitive regions and the receptor organs, such as the eyes and the ears, where information about the world is initially received. Why there is more feedback from the higher-order cognitive regions compared to the receptor organs in the formation of memory, or why there seems to be communication between the visual and auditory cortices before sending information to higher-order brain regions, is not fully understood. Researchers at HMS further explored this interaction—how and where they take place in the brain—to better understand how memory helps us make predictions about our world, and how memory (experience) alters our interpretation of sensory information. Specifically, the scientists used a mouse model and a virtual reality system to investigate the projection of axons between the auditory and visual cortices, which prior research had established exists in both humans and mice. They found that the auditory axons had both auditory and (retinotopically matched) visual responses to the primary visual cortex (V1), and the number of visually responsive axons increased as the mouse was trained to associate the auditory and visual cues. When an auditory cue was used to trigger a memory about a visual stimulus, the memory association with the auditory cue selectively suppressed neuronal response to the visual stimulus (that is, the circuit from the auditory cortex likely targets local inhibitory neurons) in V1, but only after conditioning. More broadly, this finding provides a mechanism to explain the suppression of sensory response after learned experience, and ultimately, the research helps to inform how memory affects conditions such as post-trauma stress disorder (PTSD) that results in part from the cognitive misinterpretation of sensory stimuli due to traumatic prior experience.

Visual responses of neurons inhibited (blue) compared to neurons excited (red) late in conditioning (bottom) to a visual stimulus (left) compared to control (right); inhibited neurons in V1 show increased response after conditioning to auditory input (bottom left, blue)

My rating of this study: ⭐⭐⭐

Garner AR and Keller GB. "A cortical circuit for audio-visual predictions." Nature Neuroscience.  25:98-105. 2 December 2021. https://doi.org/10.1038/s41593-021-00974-7 

EyeSyn: Eye Movement Synthesis for Virtual Reality

Article: Simulated Human Eye Movement Aims to Train Metaverse Platforms
Source: Duke University
Published: March 7, 2022
Article: Simulated Human Eye Movement Aims to Train Metaverse Platforms
Source: National Science Foundation
Published: March 30, 2022

The minutiae of eye movement and pupillary response reveal a surprising amount of information about our inner thoughts, for example, whether we are bored or excited, whether our attention is focused, and whether we are an expert or a novice at a task. Our eyes even reveal whether we are fluent in a language or whether we are reading a comic book or advanced literature. Computer engineers exploring this poetic window to our soul designed a "virtual eyes" software that simulates human eye movement to study how humans see the world and process visual information, with aims for smaller-scale uses in metaverse applications. Called EyeSyn, the generative model used publicly available data, such as videos of speakers addressing the media during press conferences or visuals of art, and compared it to data from the eye movements of actual viewers. By training on publicly available data, EyeSyn reduces the privacy concerns that usually come with collecting this sort of user data. Even when trained on small datasets, which notably alleviates the problem of sparse gaze data from human subjects, the results showed that the program could simulate distinct patterns of gaze signals and eye responses to stimuli with 90% accuracy. "The synthetic data alone isn't perfect, but it's a good starting point," the lead researcher notes, "Smaller companies can use it rather than spending the time and money on trying to build their own real-world datasets (with human subjects). And because the personalization of the algorithms can be done on local systems, people don't have to worry about their priacy eye movement data becoming part of a large database."

Eye movement data from a human subject

Comparison of four tasks between actual gaze (left) and simulated gaze (right) using EyeSyn

 
My rating of this study: ⭐⭐

Lan G, Scargill T and Gorlatova M. "EyeSyn: Psychology-inspired Eye Movement Synthesis for Gaze-based Activity Recognition." ACM/IEEE International Conference on Information Processing in Sensor Networks.  May 4–6, 2022. https://conferences.computer.org/cpsiot/pdfs/IPSN2022-6R1M30NXCSXmbVKUqzz1Of/962400a221/962400a221.pdf