Modulation of osmotic stress-induced TRPV1 expression rescues human iPSC-derived retinal ganglion cells through PKA

Comparative effectiveness of nitro dihydrocapsaicin, new synthetic derivative capsaicinoid, and capsaicin in alleviating oxidative stress and inflammation on lipopolysaccharide-stimulated corneal epithelial cells

Loss of tear homeostasis, characterized by hyperosmolarity of the ocular surface, induces cell damage through inflammation and oxidation. Transient receptor potential vanilloid 1 (TRPV1), a sensor for osmotic changes, plays a crucial role as a calcium ion channel in the pathogenesis of hypertonic-related eye diseases. Capsaicin (CAP), a potent phytochemical, alleviates inflammation during oxidative stress events by activating TRPV1. However, the pharmacological use of CAP for eye treatment is limited by its pungency. Nitro dihydrocapsaicin (NDHC) was synthesized with aromatic ring modification of CAP structure to overcome the pungent effect. We compared the molecular features of NDHC and CAP, along with their biological activities in human corneal epithelial (HCE) cells, focusing on antioxidant and anti-inflammatory activities. The results demonstrated that NDHC maintained cell viability, cell shape, and exhibited lower cytotoxicity compared to CAP-treated cells. Moreover, NDHC prevented oxidative stress and inflammation in HCE cells following lipopolysaccharide (LPS) administration. These findings underscore the beneficial effect of NDHC in alleviating ocular surface inflammation, suggesting that NDHC may serve as an alternative anti-inflammatory agent targeting TRPV1 for improving hyperosmotic stress-induced ocular surface damage.

7,8-Dihydroxiflavone protects retinal ganglion cells and promotes axonal regeneration through TrkB signaling pathway followed by AKT and ERK activation

The aim of this study was to investigate the effects of 7,8-dihydroxyflavone (7,8-DHF) in protecting retinal ganglion cells (RGCs) and promoting axonal regeneration, and to explore its potential molecular mechanisms. We used three-dimensional retinal culture system and optic nerve crush (ONC) rat models in this study. The pro-axonal regenerative effect of 7,8-DHF was determined with light microscopy observation and immunofluorescence staining of Thy1.1 and GAP43. The RGC protective function of 7,8-DHF was detected by RBPMS immunofluorescent staining and TUNEL staining. The inhibition effect of 7,8-DHF on astrocyte activation was measured using GFAP immunofluorescence and Western blotting. The protein levels of p-TrkB, p-AKT and p-ERK was examined by Western blotting and immunohistochemistry. Our results revealed that 7,8-DHF significantly promoted the average density and length of regenerated neurites and suppressed the apoptosis of GCL cells in three-dimensional culture system and significantly increased the number of RBPMS-positive cells and inhibited the GFAP expression and apoptosis of GCL cells in ONC rats. Our results also revealed that 7,8-DHF activates TrkB, AKT and ERK proteins in vivo, however, these activations can be inhibited byANA-12. In conclusion, 7,8-DHF protects RGCs and promotes axonal regeneration through the TrkB signaling pathway followed by AKT and ERK activation.

Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration

Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.

Regulation of the Membrane Trafficking of the Mechanosensitive Ion Channels TRPV1 and TRPV4 by Zonular Tension, Osmotic Stress and Activators in the Mouse Lens

Lens water transport generates a hydrostatic pressure gradient that is regulated by a dual-feedback system that utilizes the mechanosensitive transient receptor potential vanilloid (TRPV) channels, TRPV1 and TRPV4, to sense changes in mechanical tension and extracellular osmolarity. Here, we investigate whether the modulation of TRPV1 or TRPV4 activity dynamically affects their membrane trafficking. Mouse lenses were incubated in either pilocarpine or tropicamide to alter zonular tension, exposed to osmotic stress, or the TRPV1 and TRPV4 activators capsaicin andGSK1016790A (GSK101), and the effect on the TRPV1 and TRPV4 membrane trafficking in peripheral fiber cells visualized using confocal microscopy. Decreases in zonular tension caused the removal of TRPV4 from the membrane of peripheral fiber cells. Hypotonic challenge had no effect on TRPV1, but increased the membrane localization of TRPV4. Hypertonic challenge caused the insertion of TRPV1 and the removal of TRPV4 from the membranes of peripheral fiber cells. Capsaicin caused an increase in TRPV4 membrane localization, but had no effect on TRPV1; while GSK101 decreased the membrane localization of TRPV4 and increased the membrane localization of TRPV1. These reciprocal changes in TRPV1/4 membrane localization are consistent with the channels acting as mechanosensitive transducers of a dual-feedback pathway that regulates lens water transport.

Minireview: Insights into the role of TRP channels in the retinal circulation and function

Consistent with their wide distribution throughout the CNS, transcripts of all transient receptor potential (TRP) cation channel superfamily members have been detected in both neuronal and non-neuronal cells of the mammalian retina. Evidence shows that members of the TRPC (canonical, TRPC1/4/5/6), TRPV (vanilloid, TRPV1/2/4), TRPM (melastatin, TRPM1/2/3/5), TRPA (ankyrin, TRPA1), and TRPP (polycystin, TRPP2) subfamilies contribute to retinal function and circulation in health and disease, but the relevance of most TRPs has yet to be determined. Their principal role in light detection is far better understood than their participation in the control of intraocular pressure, retinal blood flow, oxidative stress, ion homeostasis, and transmitter signaling for retinal information processing. Moreover, if the therapeutic potential of targeting some TRPs to treat various retinal diseases remains speculative, recent studies highlight that vision restoration strategies are very likely to benefit from the thermo- and mechanosensitive properties of TRPs. This minireview focuses on the evidence of the past 5 years about the role of TRPs in the retina and retinal circulation, raises some possibilities about the function of TRPs in the retina, and discusses the potential sources of endogenous stimuli for TRPs in this tissue, as a reflection for future studies.

Role and Modulation of TRPV1 in Mammalian Spermatozoa: An Updated Review

Based on the abundance of scientific publications, the polymodal sensor TRPV1 is known as one of the most studied proteins within the TRP channel family. This receptor has been found in numerous cell types from different species as well as in spermatozoa. The present review is focused on analyzing the role played by this important channel in the post-ejaculatory life of spermatozoa, where it has been described to be involved in events such as capacitation, acrosome reaction, calcium trafficking, sperm migration, and fertilization. By performing an exhaustive bibliographic search, this review gathers, for the first time, all the modulators of the TRPV1 function that, to our knowledge, were described to date in different species and cell types. Moreover, all those modulators with a relationship with the reproductive process, either found in the female tract, seminal plasma, or spermatozoa, are presented here. Since the sperm migration through the female reproductive tract is one of the most intriguing and less understood events of the fertilization process, in the present work, chemotaxis, thermotaxis, and rheotaxis guiding mechanisms and their relationship with TRPV1 receptor are deeply analyzed, hypothesizing its (in)direct participation during the sperm migration. Last, TRPV1 is presented as a pharmacological target, with a special focus on humans and some pathologies in mammals strictly related to the male reproductive system.

Hereditary Optic Neuropathies: Induced Pluripotent Stem Cell-Based 2D/3D Approaches

Inherited optic neuropathies share visual impairment due to the degeneration of retinal ganglion cells (RGCs) as the hallmark of the disease. This group of genetic disorders are caused by mutations in nuclear genes or in the mitochondrial DNA (mtDNA). An impaired mitochondrial function is the underlying mechanism of these diseases. Currently, optic neuropathies lack an effective treatment, and the implementation of induced pluripotent stem cell (iPSC) technology would entail a huge step forward. The generation of iPSC-derived RGCs would allow faithfully modeling these disorders, and these RGCs would represent an appealing platform for drug screening as well, paving the way for a proper therapy. Here, we review the ongoing two-dimensional (2D) and three-dimensional (3D) approaches based on iPSCs and their applications, taking into account the more innovative technologies, which include tissue engineering or microfluidics.