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ENeuro Jun 2024Elevated intraocular pressure (IOP) triggers glaucoma by damaging the output neurons of the retina called retinal ganglion cells (RGCs). This leads to the loss of RGC...
Elevated intraocular pressure (IOP) triggers glaucoma by damaging the output neurons of the retina called retinal ganglion cells (RGCs). This leads to the loss of RGC signaling to visual centers of the brain such as the dorsolateral geniculate nucleus (dLGN), which is critical for processing and relaying information to the cortex for conscious vision. In response to altered levels of activity or synaptic input, neurons can homeostatically modulate postsynaptic neurotransmitter receptor numbers, allowing them to scale their synaptic responses to stabilize spike output. While prior work has indicated unaltered glutamate receptor properties in the glaucomatous dLGN, it is unknown whether glaucoma impacts dLGN inhibition. Here, using DBA/2J mice, which develop elevated IOP beginning at 6-7 months of age, we tested whether the strength of inhibitory synapses on dLGN thalamocortical relay neurons is altered in response to the disease state. We found an enhancement of feed-forward disynaptic inhibition arising from local interneurons along with increased amplitude of quantal inhibitory synaptic currents. A combination of immunofluorescence staining for the GABA-α1 receptor subunit, peak-scaled nonstationary fluctuation analysis, and measures of homeostatic synaptic scaling pointed to an approximately 1.4-fold increase in GABA receptors at post-synaptic inhibitory synapses, although several pieces of evidence indicate a non-uniform scaling across inhibitory synapses within individual relay neurons. Together, these results indicate an increase in inhibitory synaptic strength in the glaucomatous dLGN, potentially pointing toward homeostatic compensation for disruptions in network and neuronal function triggered by increased IOP. Elevated eye pressure in glaucoma leads to loss of retinal outputs to the dorsolateral geniculate nucleus (dLGN), which is critical for relaying information to the cortex for conscious vision. Alterations in neuronal activity, as could arise from excitatory synapse loss, can trigger homeostatic adaptations to synaptic function that attempt to maintain activity within a meaningful dynamic range, although whether this occurs uniformly at all synapses within a given neuron or is a non-uniform process is debated. Here, using a mouse model of glaucoma, we show that dLGN inhibitory synapses undergo non-uniform upregulation due to addition of post-synaptic GABA receptors. This is likely to be a neuronal adaptation to glaucomatous pathology in an important sub-cortical visual center.
PubMed: 38937109
DOI: 10.1523/ENEURO.0263-24.2024 -
Investigative Ophthalmology & Visual... Jun 2024Retinal ganglion cells (RGCs) connect the retina to the brain. Proper development of the axons and dendrites of RGCs is the basis for these cells to function as...
PURPOSE
Retinal ganglion cells (RGCs) connect the retina to the brain. Proper development of the axons and dendrites of RGCs is the basis for these cells to function as projection neurons to deliver visual information to the brain. The purpose of this study was to investigate the function of Shtn1 (which encodes shootin1) in RGC neurite development.
METHODS
Immunofluorescence (IF) was used to characterize the expression pattern of marker genes. An in vitro direct somatic cell reprogramming system was used to generate RGC-like neurons (iRGCs), which was subsequently used to study the function of Shtn1. Short-hairpin RNAs (shRNAs) were used to knock down Shtn1, and the coding sequence (CDS) of Shtn1 was used to overexpress the gene. Lentiviruses were used to deliver shRNAs or CDSs into iRGCs. The patch clamp technique was used to measure the electrophysiological properties of the iRGCs. RNA sequencing (RNA-seq) was used to examine transcriptome expression.
RESULTS
Using IF, we demonstrated that shootin1 is distinctively expressed in RGCs during the period in which RGCs actively develop and adjust the connections of their neurites with upstream and downstream neurons. Using the iRGC system, we demonstrated that Shtn1 promotes the growth and complexity of neurites and thus the electrophysiological maturation, of iRGCs. RNA-seq analyses showed that Shtn1 may also regulate gene expression and neurogenesis in iRGCs.
CONCLUSIONS
Shtn1 promotes RGC neurite development. These findings improve our understanding of the molecular machinery governing RGC neurite development and may help to optimize future RGC regeneration methods.
Topics: Retinal Ganglion Cells; Animals; Neurites; Mice; Nerve Tissue Proteins; Cellular Reprogramming; Cells, Cultured; Mice, Inbred C57BL; Patch-Clamp Techniques; Neurogenesis
PubMed: 38935030
DOI: 10.1167/iovs.65.6.41 -
Neural Regeneration Research Jun 2024Diabetic retinopathy is a prominent cause of blindness in adults, with early retinal ganglion cell (RGC) loss contributing to visual dysfunction or blindness. In the...
Diabetic retinopathy is a prominent cause of blindness in adults, with early retinal ganglion cell (RGC) loss contributing to visual dysfunction or blindness. In the brain, defects in y-aminobutyric acid (GABA) synaptic transmission are associated with pathophysiological and neurodegenerative disorders, whereas glucagon-like peptide-1 (GLP-1) has demonstrated neuroprotective effects. However, it is not yet clear whether diabetes causes alterations in inhibitory input to RGCs and whether and how GLP-1 protects against neurodegeneration in the diabetic retina through regulating inhibitory synaptic transmission to RGCs. In the present study, we used the patch-clamp technique to record GABA subtype A receptor-mediated miniature inhibitory postsynaptic currents (mIPSCs) in RGCs from streptozotocin-induced diabetes model rats. We found that early diabetes (4 weeks of hyperglycemia) decreased the frequency of GABAergic mIPSCs in RGCs without altering their amplitude, suggesting a reduction in the spontaneous release of GABA to RGCs. Topical administration of GLP-1 eyedrops over a period of 2 weeks effectively countered the hyperglycemia-induced downregulation of GABAergic mIPSC frequency, subsequently enhancing the survival of RGCs. Concurrently, the protective effects of GLP-1 on RGCs in diabetic rats were eliminated by topical administration of exendin-9-39, a specific GLP-1 receptor antagonist, or SR95531, a specific antagonist of the GABA subtype A receptor. Furthermore, extracellular perfusion of GLP-1 was found to elevate the frequencies of GABAergic mIPSCs in both ON- and OFF-type RGCs. This elevation was shown to be mediated by activation of the phosphatidylinositol-phospholipase C/inositol 1,4,5-trisphosphate receptor/Ca2+/protein kinase C signaling pathway downstream of GLP-1 receptor activation. Moreover, multielectrode array recordings revealed that GLP-1 functionally augmented the photoresponses of ON-type RGCs. Optomotor response tests demonstrated that diabetic rats exhibited reductions in visual acuity and contrast sensitivity that were significantly ameliorated by topical administration of GLP-1. These results suggest that GLP-1 facilitates the release of GABA onto RGCs through the activation of GLP-1 receptor, leading to the de-excitation of RGC circuits and the inhibition of excitotoxic processes associated with diabetic retinopathy. Collectively, our findings indicate that the GABA system has potential as a therapeutic target for mitigating early-stage diabetic retinopathy. Furthermore, the topical administration of GLP-1 eyedrops represents a non-invasive and effective treatment approach for managing early-stage diabetic retinopathy.
PubMed: 38934389
DOI: 10.4103/NRR.NRR-D-24-00001 -
Pharmaceuticals (Basel, Switzerland) Jun 2024The effects of brain-derived neurotrophic factor (BDNF) on retinal ganglion cell (RGC) survival and visual function were assessed in rat and mouse models of optic nerve...
The effects of brain-derived neurotrophic factor (BDNF) on retinal ganglion cell (RGC) survival and visual function were assessed in rat and mouse models of optic nerve (ON) crush. ONs were crushed on Day 1, followed by intravitreal injections of a vehicle or BDNF on Days 1 and 8. The spatial frequency threshold was measured using optokinetic tracking on Days 7 and 14. On Day 15, ganglion cell complex (GCC) thickness was quantified using optical coherence tomography. Furthermore, all eyes were enucleated for immunohistochemical analysis of the surviving RGC somas and axons. BDNF significantly reduced the RGC soma in mice and increased GCC thickness in intact eyes, with apparent axonal swelling in both species. It displayed significantly greater RGC soma survival in eyes with ON injury, with moderately thicker axonal bundles in both species and a thicker GCC in rats. Visual function was significantly reduced in all ON-crushed animals, regardless of BDNF treatment. Thus, we obtained a comprehensive analysis of the structural and functional impact of BDNF in intact and ON-crushed eyes in two rodent models. Our results provide a foundation for further BDNF evaluation and the design of preclinical studies on neuroprotectants using BDNF as a reference positive control.
PubMed: 38931465
DOI: 10.3390/ph17060798 -
Journal of Clinical Medicine Jun 2024(1) This research aimed to evaluate the changes in ganglion cell layer thickness (GCLT) after uncomplicated cataract surgery in patients without previous ocular...
(1) This research aimed to evaluate the changes in ganglion cell layer thickness (GCLT) after uncomplicated cataract surgery in patients without previous ocular pathology and the impact of the appearance of cystoid macular edema on the GCLT and visual acuity. (2) The evaluation of 174 patients was performed with the indication of uncomplicated cataract surgery. The variables analyzed were demographic data, best-corrected visual acuity (BCVA), cataract type and OCT (Optical Coherence Tomography) measurements of central macular thickness (CMT), and the presence of cysts and GCLT preoperatively and one day, one and three months after surgery. (3) There was a relationship between the postoperative increase in retinal GCLT and BCVA after uncomplicated cataract surgery. The presence of microcysts reduced the thickness of the GCL, which is significantly related to the loss of BCVA. The appearance of cystoid macular edema one month after surgery was also related to the preoperative CMT. There was a statistically significant decrease in preoperative GCL but a statistically significant increase in preoperative CMT in patients with microcysts one-month post-surgery. (4) There is a relationship between postoperative retinal GCLT and BCVA after uncomplicated cataract surgery. The presence of microcysts significantly reduces the thickness of the GCL, which is significantly related to the loss of BCVA.
PubMed: 38930108
DOI: 10.3390/jcm13123579 -
Medicina (Kaunas, Lithuania) May 2024Hydroxychloroquine sulfate (HCQ) is a lysosomotropic agent administered in systemic lupus erythematosus and rheumatoid arthritis that has fewer toxic effects than...
Hydroxychloroquine sulfate (HCQ) is a lysosomotropic agent administered in systemic lupus erythematosus and rheumatoid arthritis that has fewer toxic effects than chloroquine. However, HCQ may still be responsible for retinal toxicity. In this study, we observed structural changes in the retinas of experimental rats after prolonged exposure to HCQ. We investigated several aspects regarding retinal changes, at both the histopathological and ultrastructural levels. We used 96 male albino Wistar rats distributed into four equal groups (n = 24 per group): the first three groups were treated with different doses of HCQ (50, 100, and 200 mg/kg HCQ, injected intraperitoneally in a single dose daily), and the last group (the control group, n = 24) was treated with saline solution administered in the same way (0.4 mL of saline solution). The treated groups received HCQ daily for 4 months, and every month, six animals from each group were sacrificed to assess retinal changes. The eyes were examined via optical (OM) and electronic microscopy (EM). Statistical analysis was deployed, and results regarding retinal morpho-photometry were acquired. We observed structural retinal changes in both high and low doses of HCQ; while high doses determined a significant thinning of the retina, lower doses caused retinal thickening. Morphological retinal changes upon exposure to HCQ are believed to be caused by accumulated HCQ in lysosomes found in retinal ganglion cells and in the inner nuclear and photoreceptor cell layers. Such changes were most evident in the group receiving HCQ intraperitoneally in doses of 100 mg/kg for a longer period (4 months). The present study highlights histopathological and ultrastructural retinal changes induced by chronic HCQ administration, which were strongly connected to the dosage and period of exposure.
Topics: Hydroxychloroquine; Animals; Rats, Wistar; Rats; Retina; Male; Antirheumatic Agents
PubMed: 38929463
DOI: 10.3390/medicina60060846 -
Antioxidants (Basel, Switzerland) Jun 2024Oxidative stress is a key factor causing mitochondrial dysfunction and retinal ganglion cell (RGC) death in glaucomatous neurodegeneration. The cyclic adenosine...
Oxidative stress is a key factor causing mitochondrial dysfunction and retinal ganglion cell (RGC) death in glaucomatous neurodegeneration. The cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling pathway is involved in mitochondrial protection, promoting RGC survival. Soluble adenylyl cyclase (sAC) is a key regulator of the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling pathway, which is known to protect mitochondria and promote RGC survival. However, the precise molecular mechanisms connecting the sAC-mediated signaling pathway with mitochondrial protection in RGCs against oxidative stress are not well characterized. Here, we demonstrate that sAC plays a critical role in protecting RGC mitochondria from oxidative stress. Using mouse models of oxidative stress induced by ischemic injury and paraquat administration, we found that administration of bicarbonate, as an activator of sAC, protected RGCs, blocked AMP-activated protein kinase activation, inhibited glial activation, and improved visual function. Moreover, we found that this is the result of preserving mitochondrial dynamics (fusion and fission), promoting mitochondrial bioenergetics and biogenesis, and preventing metabolic stress and apoptotic cell death. Notably, the administration of bicarbonate ameliorated mitochondrial dysfunction in RGCs by enhancing mitochondrial biogenesis, preserving mitochondrial structure, and increasing ATP production in oxidatively stressed RGCs. These findings suggest that activating sAC enhances the mitochondrial structure and function in RGCs to counter oxidative stress, consequently promoting RGC protection. We propose that modulation of the sAC-mediated signaling pathway has therapeutic potential acting on RGC mitochondria for treating glaucoma and other retinal diseases.
PubMed: 38929182
DOI: 10.3390/antiox13060743 -
Diagnostics (Basel, Switzerland) Jun 2024Optical coherence tomography (OCT) is a non-invasive imaging technique based on the principle of low-coherence interferometry that captures detailed images of ocular...
Optical coherence tomography (OCT) is a non-invasive imaging technique based on the principle of low-coherence interferometry that captures detailed images of ocular structures. Multiple sclerosis (MS) is a neurodegenerative disease that can lead to damage of the optic nerve and retina, which can be depicted by OCT. The purpose of this pilot study is to determine whether macular OCT can be used as a biomarker in the detection of retrochiasmal lesions of the visual pathway in MS patients. We conducted a prospective study in which we included 52 MS patients and 27 healthy controls. All participants underwent brain MRI, visual field testing, and OCT evaluation of the thicknesses of the peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell layer (GCL), and macular inner plexiform layer (IPL). OCT measurements were adjusted for optic neuritis (ON). VF demonstrated poor capability to depict a retrochiasmal lesion identified by brain MRI (PPV 0.50). In conclusion, the OCT analysis of the macula appears to excel in identifying retrochiasmal MS lesions compared to VF changes. The alterations in the GCL and IPL demonstrate the most accurate detection of retrochiasmal visual pathway changes in MS patients.
PubMed: 38928637
DOI: 10.3390/diagnostics14121221 -
International Journal of Molecular... Jun 2024Polyamine (PA) spermidine (SPD) plays a crucial role in aging. Since SPD accumulates in glial cells, particularly in Müller retinal cells (MCs), the expression of the...
Polyamine (PA) spermidine (SPD) plays a crucial role in aging. Since SPD accumulates in glial cells, particularly in Müller retinal cells (MCs), the expression of the SPD-synthesizing enzyme spermidine synthase (SpdS) in Müller glia and age-dependent SpdS activity are not known. We used immunocytochemistry, Western blot (WB), and image analysis on rat retinae at postnatal days 3, 21, and 120. The anti-glutamine synthetase (GS) antibody was used to identify glial cells. In the neonatal retina (postnatal day 3 (P3)), SpdS was expressed in almost all progenitor cells in the neuroblast. However, by day 21 (P21), the SpdS label was pronouncedly expressed in multiple neurons, while GS labels were observed only in radial Müller glial cells. During early cell adulthood, at postnatal day 120 (P120), SpdS was observed solely in ganglion cells and a few other neurons. Western blot and semi-quantitative analyses of SpdS labeling showed a dramatic decrease in SpdS at P21 and P120 compared to P3. In conclusion, the redistribution of SpdS with aging indicates that SPD is first synthesized in all progenitor cells and then later in neurons, but not in glia. However, MCs take up and accumulate SPD, regardless of the age-associated decrease in SPD synthesis in neurons.
Topics: Animals; Rats; Spermidine Synthase; Retina; Ependymoglial Cells; Aging; Spermidine; Neuroglia; Animals, Newborn
PubMed: 38928162
DOI: 10.3390/ijms25126458 -
International Journal of Molecular... Jun 2024We present a case involving a patient whose clinical phenotype aligns with oculocutaneous albinism (OCA), yet exhibits a complex genotype primarily characterized by...
We present a case involving a patient whose clinical phenotype aligns with oculocutaneous albinism (OCA), yet exhibits a complex genotype primarily characterized by variants of unknown significance (VUS). An 11-year-old boy manifested iris hypopigmentation and translucency, pronounced photophobia, diminished visual acuity and stereopsis, nystagmus, reduced pigmentation of the retina, and foveal hypoplasia. Genetic testing was performed. A heterozygous missense VUS c.230A>G, p.(Gln77Arg), a heterozygous missense VUS c.1307G>C, p.(Gly436Ala), and a heterozygous missense variant c.1205G>A, p.(Arg402Gln) which was classified as a risk factor, were identified. We hypothesized that the c.1307G>C, p.(Gly436Ala) variant is in genetic disequilibrium with the c.1205G>A, p.(Arg402Gln) variant leading to deficient expression of melanogenic enzymes in retinal cells, resulting in the manifestation of mild OCA. Additionally, this study represents the case where we did not detect chiasmal misrouting in visual evoked potentials, nor did we observe a shift in the distribution of ganglion cell thickness from a temporal to a central position. Moreover, our patient's case supports the probable benign nature of the c.230A>G, p.(Gln77Arg) variant.
Topics: Humans; Male; Child; Calpain; Monophenol Monooxygenase; Mutation, Missense; Vitreoretinopathy, Proliferative; Albinism, Oculocutaneous; Phenotype; Pedigree
PubMed: 38928147
DOI: 10.3390/ijms25126442