Current and Future Directions in Developing Effective Treatments for PRPH2-Associated Retinal Diseases: A Workshop Report.

Purpose and Methods: A workshop of affected individuals and their families, clinicians, researchers, and industry representatives was convened in March 2023 to define the knowledge landscape of peripherin 2 (PRPH2) biology and identify challenges and opportunities towards developing PRPH2-associated inherited retinal disease (IRD) treatments. Results: The results of an online survey and presentations from affected individuals and their family members revealed disease characteristics and impacts on daily living. Scientific sessions highlighted the significant heterogeneity in clinical presentation of PRPH2-related retinopathy; PRPH2's crucial function in rod and cone outer segment formation and maintenance; the usefulness of existing animal and cellular models for understanding disease pathophysiology; and possible therapeutic approaches for autosomal dominant PRPH2-associated IRDs, including gene-specific therapies and gene-agnostic approaches. Priority gaps identified by the workshop included having a more complete understanding of PRPH2's fundamental biology and factors contributing to PRPH2-related disease phenotypic diversity, establishing genotype-phenotype correlations, and creating additional models to probe the functional consequences of PRPH2 variants and to test therapies. Additionally, a natural history study involving a large number of participants is required to more fully characterize PRPH2-related disease progression, aiding in interventional clinical trial design. Conclusions: Because PRPH2-associated IRDs are rare, maximizing opportunities for communication and collaboration among stakeholders, such as that provided by the workshop, is crucial to overcome the challenges to developing effective treatments and improve the lives of affected individuals. Translational Relevance: Fostering communication among stakeholders to identify knowledge gaps, therapeutic challenges, and potential opportunities toward developing effective treatments for PRPH2-related IRDs.

The expression of intermediate filaments in the abomasum of ruminants: A comparative study.

Intermediate filaments (IFs) are key molecular factors of the cell and have been reported to play an important role in maintaining the structural integrity and functionality of the abomasum. This study was designed to determine the regional distribution, cellular localization and expression of several IFs, including CK8, CK18, CK19, vimentin, desmin, peripherin and nestin, as well as the connective tissue component laminin, in the bovine, ovine and caprine abomasa. Immunohistochemical analyses demonstrated varying levels of expression of CK8, CK18, CK19, vimentin, desmin, nestin, peripherin and laminin in the bovine, ovine and caprine abomasa. CK8 immunoreactions were particularly evident in the luminal and glandular epithelia of the glands found in the abomasal cardia, fundus and pylorus in all three species. In the bovine abomasum, CK18 immunoreactions were stronger in the parietal cells, compared to the chief cells. In the abomasum of all three species, the smooth muscle as well as the smooth muscle cells of the vascular media in the cardiac, fundic and pyloric regions showed strong immunoreactivity. In all three species, the cardiac, fundic and pyloric regions of the abomasum showed strong peripherin and nestin immunoreactions in the luminal and glandular epithelial cells, stromal and smooth muscle cells, nervous plexuses and blood vessels. The expression patterns of IFs and laminin in the ruminant abomasum suggest that these proteins play a structural role in the cytoskeleton and are effective in maintaining abomasal tissue integrity and stability.

Downregulation of rhodopsin is an effective therapeutic strategy in ameliorating peripherin-2-associated inherited retinal disorders.

Given the absence of approved treatments for pathogenic variants in Peripherin-2 (PRPH2), it is imperative to identify a universally effective therapeutic target for PRPH2 pathogenic variants. To test the hypothesis that formation of the elongated discs in presence of PRPH2 pathogenic variants is due to the presence of the full complement of rhodopsin in absence of the required amounts of functional PRPH2. Here we demonstrate the therapeutic potential of reducing rhodopsin levels in ameliorating disease phenotype in knockin models for p.Lys154del (c.458-460del) and p.Tyr141Cys (c.422 A > G) in PRPH2. Reducing rhodopsin levels improves physiological function, mitigates the severity of disc abnormalities, and decreases retinal gliosis. Additionally, intravitreal injections of a rhodopsin-specific antisense oligonucleotide successfully enhance the physiological function of photoreceptors and improves the ultrastructure of discs in mutant mice. Presented findings shows that reducing rhodopsin levels is an effective therapeutic strategy for the treatment of inherited retinal degeneration associated with PRPH2 pathogenic variants.

[Role of endosomal pathway in the ciliary transport and the membrane organization of outer segment disc membrane in photoreceptors].

A photoreceptor is a specialized neuron that is responsible for the conversion of light into an electrical signal. Photoreceptors are classified into rods and cones, and both photoreceptors possess light-sensing ciliary organelles called outer segments (OSs), anchored in the cells by a microtubule-based axoneme. The OS consists of a stack of disc membranes, which are abundant for the retinal phototransduction proteins such as rhodopsin. Recently, modern protein synchronization techniques using in vivo transfection in rodents revealed that rhodopsin transits through Rab11-positive recycling endosomes, preferentially entering the OS in the dark. Moreover, Peripherin-2 (PRPH2, also called retinal degeneration slow, RDS), a photoreceptor-specific tetraspanin protein essential for the morphogenesis of disc membranes, is delivered to the OS following complementary to that of rhodopsin. Various PRPH2 disease-causing mutations have been found in humans, and most of the mutations in the cytosolic C-terminus of PRPH2 are linked to cone-dominant macular dystrophies. It has been shown that the late endosome is the waystation that sorts newly synthesized PRPH2 into the cilium. The multiple C-terminal motifs of PRPH2 regulate its late endosome and ciliary targeting through ubiquitination and binding to an Endosomal Sorting Complexes Required for Transport (ESCRT) component, Hrs. These findings suggest that the late endosomes play an important role in the biosynthetic pathway of ciliary proteins and can be a new therapeutic target for the diseases caused by ciliary defects.

Identification and cellular localization in Xenopus laevis photoreceptors of three Peripherin-2 family members, Prph2, Rom1 and Gp2l, which arose from gene duplication events in the common ancestors of jawed vertebrates.

Rod and cone photoreceptors are named for the distinct morphologies of their outer segment organelles, which are either cylindrical or conical, respectively. The morphologies of the stacked disks that comprise the rod and cone outer segments also differ: rod disks are completely sealed and are discontinuous from the plasma membrane, while cone disks remain partially open to the extracellular space. These morphological differences between photoreceptor types are more prominent in non-mammalian vertebrates, whose cones typically possess a greater proportion of open disks and are more tapered in shape. In mammals, the tetraspanin prph2 generates and maintains the highly curved disk rim regions by forming extended oligomeric structures with itself and a structurally similar paralog, rom1. Here we determined that in addition to these two proteins, there is a third Prph2 family paralog in most non-mammalian vertebrate species, including X. laevis: Glycoprotein 2-like protein or "Gp2l". A survey of multiple genome databases revealed a single invertebrate Prph2 'pro-ortholog' in Amphioxus, several echinoderms and in a diversity of protostomes indicating an ancient divergence from other tetraspanins. Based on phylogenetic analysis, duplication of the vertebrate predecessor likely gave rise to the Gp2l and Prph2/Rom1 clades, with a further duplication distinguishing the Prph2 and Rom1 clades. Mammals have lost Gp2l and their Rom1 has undergone a period of accelerated evolution such that it has lost several features that are retained in non-mammalian vertebrate Rom1. Specifically, Prph2, Gp2l and non-mammalian Rom1 encode proteins with consensus N-linked glycosylation and outer segment localization signals; mammalian rom1 lacks these motifs. We determined that X. laevis gp2l is expressed exclusively in cones and green rods, while X. laevis rom1 is expressed exclusively in rods, and prph2 is present in both rods and cones. The presence of three Prph2-related genes with distinct expression patterns as well as the rapid evolution of mammalian Rom1, may contribute to the more pronounced differences in morphology between rod and cone outer segments and rod and cone disks observed in non-mammalian versus mammalian vertebrates.

ROM1 is redundant to PRPH2 as a molecular building block of photoreceptor disc rims.

Visual signal transduction takes place within a stack of flattened membranous 'discs' enclosed within the light-sensitive photoreceptor outer segment. The highly curved rims of these discs, formed in the process of disc enclosure, are fortified by large hetero-oligomeric complexes of two homologous tetraspanin proteins, PRPH2 (a.k.a. peripherin-2 or rds) and ROM1. While mutations in PRPH2 affect the formation of disc rims, the role of ROM1 remains poorly understood. In this study, we found that the knockout of ROM1 causes a compensatory increase in the disc content of PRPH2. Despite this increase, discs of ROM1 knockout mice displayed a delay in disc enclosure associated with a large diameter and lack of incisures in mature discs. Strikingly, further increasing the level of PRPH2 rescued these morphological defects. We next showed that disc rims are still formed in a knockin mouse in which the tetraspanin body of PRPH2 was replaced with that of ROM1. Together, these results demonstrate that, despite its contribution to the formation of disc rims, ROM1 can be replaced by an excess of PRPH2 for timely enclosure of newly forming discs and establishing normal outer segment structure.

Photoreceptor disc incisures form as an adaptive mechanism ensuring the completion of disc enclosure.

The first steps of vision take place within a stack of tightly packed disc-shaped membranes, or 'discs', located in the outer segment compartment of photoreceptor cells. In rod photoreceptors, discs are enclosed inside the outer segment and contain deep indentations in their rims called 'incisures'. The presence of incisures has been documented in a variety of species, yet their role remains elusive. In this study, we combined traditional electron microscopy with three-dimensional electron tomography to demonstrate that incisures are formed only after discs become completely enclosed. We also observed that, at the earliest stage of their formation, discs are not round as typically depicted but rather are highly irregular in shape and resemble expanding lamellipodia. Using genetically manipulated mice and frogs and measuring outer segment protein abundances by quantitative mass spectrometry, we further found that incisure size is determined by the molar ratio between peripherin-2, a disc rim protein critical for the process of disc enclosure, and rhodopsin, the major structural component of disc membranes. While a high perpherin-2 to rhodopsin ratio causes an increase in incisure size and structural complexity, a low ratio precludes incisure formation. Based on these data, we propose a model whereby normal rods express a modest excess of peripherin-2 over the amount required for complete disc enclosure in order to ensure that this important step of disc formation is accomplished. Once the disc is enclosed, the excess peripherin-2 incorporates into the rim to form an incisure.

Peripherin is a biomarker of axonal damage in peripheral nervous system disease.

Valid, responsive blood biomarkers specific to peripheral nerve damage would improve management of peripheral nervous system (PNS) diseases. Neurofilament light chain (NfL) is sensitive for detecting axonal pathology but is not specific to PNS damage, as it is expressed throughout the PNS and CNS. Peripherin, another intermediate filament protein, is almost exclusively expressed in peripheral nerve axons. We postulated that peripherin would be a promising blood biomarker of PNS axonal damage. We demonstrated that peripherin is distributed in sciatic nerve, and to a lesser extent spinal cord tissue lysates, but not in brain or extra-neural tissues. In the spinal cord, anti-peripherin antibody bound only to the primary cells of the periphery (anterior horn cells, motor axons and primary afferent sensory axons). In vitro models of antibody-mediated axonal and demyelinating nerve injury showed marked elevation of peripherin levels only in axonal damage and only a minimal rise in demyelination. We developed an immunoassay using single molecule array technology for the detection of serum peripherin as a biomarker for PNS axonal damage. We examined longitudinal serum peripherin and NfL concentrations in individuals with Guillain-Barré syndrome (GBS, n = 45, 179 time points), chronic inflammatory demyelinating polyradiculoneuropathy (CIDP, n = 35, 70 time points), multiple sclerosis (n = 30), dementia (as non-inflammatory CNS controls, n = 30) and healthy individuals (n = 24). Peak peripherin levels were higher in GBS than all other groups (median 18.75 pg/ml versus < 6.98 pg/ml, P < 0.0001). Peak NfL was highest in GBS (median 220.8 pg/ml) and lowest in healthy controls (median 5.6 pg/ml), but NfL did not distinguish between CIDP (17.3 pg/ml), multiple sclerosis (21.5 pg/ml) and dementia (29.9 pg/ml). While peak NfL levels were higher with older age (rho = +0.39, P < 0.0001), peak peripherin levels did not vary with age. In GBS, local regression analysis of serial peripherin in the majority of individuals with three or more time points of data (16/25) displayed a rise-and-fall pattern with the highest value within the first week of initial assessment. Similar analysis of serial NfL concentrations showed a later peak at 16 days. Group analysis of serum peripherin and NfL levels in GBS and CIDP patients were not significantly associated with clinical data, but in some individuals with GBS, peripherin levels appeared to better reflect clinical outcome measure improvement. Serum peripherin is a promising new, dynamic and specific biomarker of acute PNS axonal damage.

Role of the Intermediate Filament Protein Peripherin in Health and Disease.

Intermediate filaments are the most heterogeneous class among cytoskeletal elements. While some of them have been well-characterized, little is known about peripherin. Peripherin is a class III intermediate filament protein with a specific expression in the peripheral nervous system. Epigenetic modifications are involved in this cell-type-specific expression. Peripherin has important roles in neurite outgrowth and stability, axonal transport, and axonal myelination. Moreover, peripherin interacts with proteins involved in vesicular trafficking, signal transduction, DNA/RNA processing, protein folding, and mitochondrial metabolism, suggesting a role in all these processes. This review collects information regarding peripherin gene regulation, post-translational modifications, and functions and its involvement in the onset of a number of diseases.

Synergic Effect of Combined Therapy of Hyperbaric Oxygen and Adipose-Derived Mesenchymal Stem Cells on Improving Locomotor Recovery After Acute Traumatic Spinal Cord Injury in Rat Mainly Through Downregulating Inflammatory and Cell-Stress Signalings.

This study tested whether combined hyperbaric oxygen (HBO) and allogenic adipose-derived mesenchymal stem cells (ADMSCs) would be superior to either one for improving the locomotor recovery in rat after acute traumatic spinal cord injury (TSCI) in rat. Adult-male Sprague-Dawley rats were equally categorized into group 1 (sham-operated control), group 2 (TSCI), group 3 (TSCI + HBO for 1.5 h/day for 14 consecutive days after TSCI), group 4 (TSCI + ADMSCs/1.2 × 106 cells by intravenous injection at 3 h and days 1/2 after TSCI), and group 5 (TSCI + HBO + ADMSCs), euthanized, and spinal cord tissue was harvested by day 49 after TSCI. The protein expressions of oxidative-stress (NOX-1/NOX-2), inflammatory-signaling (TLR-4/MyD88/IL-1ß/TNF-α/substance-p), cell-stress signaling (PI3K/p-AKT/p-mTOR), and the voltage-gated sodium channel (Nav1.3/1.8/1.9) biomarkers were highest in group 2, lowest in group 1, and significantly lower in group 5 than in groups 3/4 (all P <0.0001), but they did not differ between groups 3 and 4. The spinal cord damaged area, the cellular levels of inflammatory/DNA-damaged biomarkers (CD68+/GFAP+/γ-H2AX+ cells), mitogen-activated protein kinase family biomarkers (p-P38/p-JNK/p-ERK1/2), and cellular expressions of voltage-gated sodium channel (Nav.1.3, Nav.1.8, and Nav.1.9 in NF200+ cells) as well as the pain-facilitated cellular expressions (p-P38+/peripherin+ cells, p-JNK+/peripherin+ cells, p-ERK/NF200+ cells) exhibited an identical pattern of inflammation, whereas the locomotor recovery displayed an opposite pattern of inflammation among the groups (all P < 0.0001). Combined HBO-ADMSCs therapy offered additional benefits for preserving the neurological architecture and facilitated the locomotor recovery against acute TSCI.

Synergic Effect of Early Administration of Probiotics and Adipose-Derived Mesenchymal Stem Cells on Alleviating Inflammation-Induced Chronic Neuropathic Pain in Rodents.

This study investigated the hypothesis that probiotics enhanced the therapeutic effect of adipose-derived mesenchymal stem cells (ADMSCs) on alleviating neuropathic pain (NP) due to chronic constriction injury (CCI) mainly through regulating the microbiota in rats. SD rats (n = 50) were categorized into group 1 (sham-control), group 2 (NP), group 3 (NP + probiotics (i.e., 1.5 billion C.F.U./day/rat, orally 3 h after NP procedure, followed by QOD 30 times)), group 4 (NP + ADMSCs (3.0 × 105 cells) 3 h after CCI procedure, followed by QOD six times (i.e., seven times in total, i.e., mimic a clinical setting of drug use) and group 5 (NP + probiotics + ADMSCs (3.0 × 105 cells)) and euthanized by day 60 after NP induction. By day 28 after NP induction, flow-cytometric analysis showed circulating levels of early (AN-V+/PI−) and late (AN-V+/PI+) apoptotic, and three inflammatory (CD11b-c+, Ly6G+ and MPO+) cells were lowest in group 1 and significantly progressively reduced in groups 2 to 5 (all p < 0.0001). By days 7, 14, 21, 28, and 60 after CCI, the thresholds of thermal paw withdrawal latency (PWL) and mechanical paw withdrawal threshold (PWT) were highest in group 1 and significantly progressively increased in groups 2 to 5 (all p < 0.0001). Numbers of pain-connived cells (Nav1.8+/peripherin+, p-ERK+/peripherin+, p-p38+/peripherin+ and p-p38+/NF200+) and protein expressions of inflammatory (p-NF-κB, IL-1ß, TNF-α and MMP-9), apoptotic (cleaved-caspase-3, cleaved-PARP), oxidative-stress (NOX-1, NOX-2), DNA-damaged (γ-H2AX) and MAPK-family (p-P38, p-JNK, p-ERK1/2) biomarkers as well as the protein levels of Nav.1.3, Nav.1.8, and Nav.1.9 in L4-L5 in dorsal root ganglia displayed an opposite pattern of mechanical PWT among the groups (all p < 0.0001). In conclusion, combined probiotic and ADMSC therapy was superior to merely one for alleviating CCI-induced NP mainly through suppressing inflammation and oxidative stress.

Quantification of CGRP-immunoreactive myenteric neurons in mouse colon.

Quantitative data of biological systems provide valuable baseline information for understanding pathology, experimental perturbations, and computational modeling. In mouse colon, calcitonin gene-related peptide (CGRP) is expressed by myenteric neurons with multiaxonal (Dogiel type II) morphology, characteristic of intrinsic primary afferent neurons (IPANs). Analogous neurons in other species and gut regions represent 5-35% of myenteric neurons. We aimed to quantify proportions of CGRP-immunopositive (CGRP+) myenteric neurons. Colchicine-treated wholemount preparations of proximal, mid, and distal colon were labeled for HuC/D, CGRP, nitric oxide synthase (NOS), and peripherin (Per). The pan-neuronal markers (Hu+/Per+) co-labeled 94% of neurons. Hu+/Per- neurons comprised ∼6%, but Hu-/Per+ cells were rare. Thus, quantification was based on Hu+ myenteric neurons (8576 total; 1225 ± 239 per animal, n = 7). CGRP+ cell bodies were significantly larger than the average of all Hu+ neurons (329 ± 13 vs. 261 ± 12 µm2 , p < .0001). CGRP+ neurons comprised 19% ± 3% of myenteric neurons without significant regional variation. NOS+ neurons comprised 42% ± 2% of myenteric neurons overall, representing a lower proportion in proximal colon, compared to mid and distal colon (38% ± 2%, 44% ± 2%, and 44% ± 3%, respectively). Peripherin immunolabeling revealed cell body and axonal morphology in some myenteric neurons. Whether all CGRP+ neurons were multiaxonal could not be addressed using peripherin immunolabeling. However, of 118 putatively multiaxonal neurons first identified based on peripherin immunoreactivity, all were CGRP+ (n = 4). In conclusion, CGRP+ myenteric neurons in mouse colon were comprehensively quantified, occurring within a range expected of a putative IPAN marker. All Per+ multiaxonal neurons, characteristic of Dogiel type II/IPAN morphology, were CGRP+.

Integrative study of gene expression datasets in retinal samples of Diabetic Retinopathy.

Diabetic Retinopathy is prevalent among patients with uncontrolled hyperglycemia resulting in vision loss. Despite numerous challenges to create a link among these conditions, the characterization of pathological neovascularization causing retinal damage due to the prognosis of early non-proliferative diabetic retinopathy to late proliferative diabetic retinopathy needs deep understanding. In this study, meta-analysis-based integration of gene expression datasets for the fibrovascular membrane of PDR and neural retina of NPDR were compared, to investigate the differentially expressed genes involved in retinal angiogenesis. Human samples with gene expression profiling of the same experiment type and platform with sufficient information for analysis were included in the study. The studies from cell lines and non-human studies, human samples that include serum, cornea, lens, and/or other ocular tissues or fluids, and studies that lack basic information for analysis were excluded. The microarray datasets available in the Gene Expression Omnibus database of the early and late stages in DR were screened to find common gene expression profiles. Using the INMEX bioinformatics tool, significantly upregulated and downregulated genes in the neural retina of Non-Proliferative Diabetic Retinopathy and fibrovascular membrane of Proliferative Diabetic Retinopathy were compared and studied by the combine effect size method. Using the STRING database PPI network, 50 upregulated and 50 downregulated genes were used to find the key candidate genes involved in retinal disease/degeneration in eye/retinal tissues. In the extensive gene expression meta-analysis performed using INMEX bioinformatics tool, overall, 7935 differentially expressed genes were identified and the respective heatmap was created by using the visualization tools of INVEX. STRING database PPI network identified Retinol Binding Protein 3, Neural Retina Leucine Zipper, S-Antigen Visual Arrestin, Peripherin 2, and Aryl Hydrocarbon Receptor Interacting Protein Like-1 to be the most highly ranked hub genes. The newly discovered potential genes related to retinal angiogenesis causing FVM formation in DR may provide insight into the cellular pathogenesis of NPDR to PDR.

Evaluation of peripherin in biofluids of patients with motor neuron diseases.

Peripherin (PRPH), a type III intermediate filament, assembles with neurofilaments in neurons of the peripheral nervous system, including lower motor neurons (LMN). To evaluate the role of PRPH in LMN degeneration, we assessed PRPH and neurofilament light chain (NfL) in cerebrospinal fluid (CSF) and serum of 91 patients with motor neuron diseases (MND) and 69 controls. Overall, we found PRPH to be more concentrated in serum than in CSF. Serum PRPH resulted significantly increased in MND patients but it was unrelated to CSF-NfL or survival in the amyotrophic lateral sclerosis (ALS) subset. PRPH might represent a marker of LMN involvement.

Nano-scale resolution of native retinal rod disk membranes reveals differences in lipid composition.

Photoreceptors rely on distinct membrane compartments to support their specialized function. Unlike protein localization, identification of critical differences in membrane content has not yet been expanded to lipids, due to the difficulty of isolating domain-specific samples. We have overcome this by using SMA to coimmunopurify membrane proteins and their native lipids from two regions of photoreceptor ROS disks. Each sample's copurified lipids were subjected to untargeted lipidomic and fatty acid analysis. Extensive differences between center (rhodopsin) and rim (ABCA4 and PRPH2/ROM1) samples included a lower PC to PE ratio and increased LC- and VLC-PUFAs in the center relative to the rim region, which was enriched in shorter, saturated FAs. The comparatively few differences between the two rim samples likely reflect specific protein-lipid interactions. High-resolution profiling of the ROS disk lipid composition gives new insights into how intricate membrane structure and protein activity are balanced within the ROS, and provides a model for future studies of other complex cellular structures.

Restoration of visual function in advanced disease after transplantation of purified human pluripotent stem cell-derived cone photoreceptors.

Age-related macular degeneration and other macular diseases result in the loss of light-sensing cone photoreceptors, causing irreversible sight impairment. Photoreceptor replacement may restore vision by transplanting healthy cells, which must form new synaptic connections with the recipient retina. Despite recent advances, convincing evidence of functional connectivity arising from transplanted human cone photoreceptors in advanced retinal degeneration is lacking. Here, we show restoration of visual function after transplantation of purified human pluripotent stem cell-derived cones into a mouse model of advanced degeneration. Transplanted human cones elaborate nascent outer segments and make putative synapses with recipient murine bipolar cells (BCs), which themselves undergo significant remodeling. Electrophysiological and behavioral assessments demonstrate restoration of surprisingly complex light-evoked retinal ganglion cell responses and improved light-evoked behaviors in treated animals. Stringent controls exclude alternative explanations, including material transfer and neuroprotection. These data provide crucial validation for photoreceptor replacement therapy and for the potential to rescue cone-mediated vision.

The common marmoset as suitable nonhuman alternative for the analysis of primate cochlear development.

Cochlear development is a complex process with precise spatiotemporal patterns. A detailed understanding of this process is important for studies of congenital hearing loss and regenerative medicine. However, much of our understanding of cochlear development is based on rodent models. Animal models that bridge the gap between humans and rodents are needed. In this study, we investigated the development of hearing organs in a small New World monkey species, the common marmoset (Callithrix jacchus). We describe the general stages of cochlear development in comparison with those of humans and mice. Moreover, we examined more than 25 proteins involved in cochlear development and found that expression patterns were generally conserved between rodents and primates. However, several proteins involved in supporting cell processes and neuronal development exhibited interspecific expression differences. Human fetal samples for studies of primate-specific cochlear development are extremely rare, especially for late developmental stages. Our results support the use of the common marmoset as an effective alternative for analyses of primate cochlear development.

Genetic factors associated with age-related macular degeneration: identification of a novel PRPH2 single nucleotide polymorphism associated with increased risk of the disease.

PURPOSE: Age-related macular degeneration (AMD) is associated with multiple environmental and genetic risk factors. Two main risk factors for AMD are variants in the CFH and ARMS2/HTRA1 genes. We investigated over 2000 variants in AMD patients and controls using high-throughput sequencing methods to search for variants associated with AMD. METHODS: A total of 296 AMD patients and 100 controls were enrolled in this study. Genetic analysis was performed with the Illumina NextSeq 500 system. RESULTS: Multivariate analysis of patients and controls, adjusted for age, sex and smoking status (pack-years), revealed that three SNPs were strong risk factors independently associated with AMD: CFH Y402H, ARMS A69S and PRPH2 c.582-67T>A (rs3818086). The TC genotype in CFH Y402H was associated with 1.90-fold higher odds, and the CC genotype was associated with 5.66-fold higher odds of AMD compared with the TT genotype. The GT genotype in ARMS A69S was associated with 2.40-fold higher odds, and the TT genotype was associated with 6.75-fold higher odds of disease compared with the GG genotype. In the case of rs3818086, the A allele could be considered a 'risk' allele, since AA + TA genotypes were associated with 2.33-fold higher odds of AMD compared with the TT genotype. CONCLUSIONS: Although PRPH2 mutations have been previously implicated in various forms of retinal degeneration, to the best of our knowledge, this study is the first to show that the rs3818086 variant increases the risk for AMD more than two times. Further studies on larger cohorts are required to elucidate how this variant affects protein structure.

Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration.

The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)P23H/+ and Prph2Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in RhoP23H/+/Rtbdn-/- and Prph2Y141C/+/Rtbdn-/- retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.

Functional coculture of sympathetic neurons and cardiomyocytes derived from human-induced pluripotent stem cells.

Sympathetic neurons (SNs) capable of modulating the heart rate of murine cardiomyocytes (CMs) can be differentiated from human stem cells. The electrophysiological properties of human stem cell-derived SNs remain largely uncharacterized, and human neurocardiac cocultures remain to be established. Here, we have adapted previously published differentiation and coculture protocols to develop feeder-free SNs using human-induced pluripotent stem cells (hiPSCs). hiPSC-SNs were characterized in monoculture and coculture with hiPSC-CMs, using antibody labeling, enzyme-linked immunosorbent assay, and whole cell patch-clamp electrophysiology techniques. hiPSC-SNs stained positive for peripherin, tyrosine hydroxylase, and nicotinic acetylcholine receptors, the latter two colocalizing in somas and synaptic varicosities. hiPSC-SNs functionally matured in vitro and exhibited healthy resting membrane potentials (average = -61 ± 0.7 mV), secreted norepinephrine upon activation, and generated synaptic and action currents and inward and outward voltage-dependent currents. All hiPSC-SNs fired action potentials in response to current injection, local application of potassium, or spontaneously, followed by short-medium afterhyperpolarizations. hiPSC-SNs could successfully be maintained in coculture with hiPSC-CMs, and this induced further development of hiPSC-SN action potential kinetics. To test functional coupling between the neurons and cardiomyocytes, the hiPSC-CM beating response to nicotine-induced norepinephrine release was assessed. In neurocardiac cocultures, nicotine exposure significantly increased the hiPSC-CM spontaneous beating rate, but not in hiPSC-CM monocultures, supporting nicotinic neuronal hiPSC-SN stimulation directly influencing hiPSC-CM function. Our data show the development and characterization of electrophysiologically functional hiPSC-SNs capable of modulating the beating rate of hiPSC-CMs in vitro. These human cocultures provide a novel multicellular model to study neurocardiac modulation under physiological and pathological conditions.NEW & NOTEWORTHY We present data on a functional coculture between human-induced pluripotent stem cell-derived sympathetic neurons and cardiomyocytes. Moreover, this study adds significantly to the available data on the electrophysiological function of human-induced pluripotent stem cell-derived sympathetic neurons.