Administration of brain-derived neurotrophic factor suppresses the expression of heat shock protein 27 in rat retinal ganglion cells following axotomy

Small Heat Shock Proteins in Retinal Diseases

This review summarizes the latest findings on small heat shock proteins (sHsps) in three major retinal diseases: glaucoma, diabetic retinopathy, and age-related macular degeneration. A general description of the structure and major cellular functions of sHsps is provided in the introductory remarks. Their role in specific retinal diseases, highlighting their regulation, role in pathogenesis, and possible use as therapeutics, is discussed.

The protective role of HSP27 in ocular diseases

Heat shock proteins (HSPs) are stress-induced proteins that are important constituents of the cell's defense system. The activity of HSPs enhances when the cell undergoes undesirable environmental conditions like stress. The protective roles of HSPs are due to their molecular chaperone and anti-apoptotic functions. HSPs have a central role in the eye, and their malfunction has been associated with the manifestation of ocular diseases. Heat shock protein 27 (HSP27, HSPB1) is present in various ocular tissues, and it has been found to protect the eye from disease states such as retinoblastoma, uveal melanoma, glaucoma, and cataract. But some recent studies have shown the destructive role of HSP27 on retinal ganglionic cells. Thus, this article summarizes the role of heat shock protein 27 in eye and ocular diseases and will focus on the expression, regulation, and function of HSP27 in ocular complications.

Cellular stress mechanisms of prenatal maternal stress: Heat shock factors and oxidative stress

Development of the brain prenatally is affected by maternal experience and exposure. Prenatal maternal psychological stress changes brain development and results in increased risk for neuropsychiatric disorders. In this review, multiple levels of prenatal stress mechanisms (offspring brain, placenta, and maternal physiology) are discussed and their intersection with cellular stress mechanisms explicated. Heat shock factors and oxidative stress are closely related to each other and converge with the inflammation, hormones, and cellular development that have been more deeply explored as the basis of prenatal stress risk. Increasing evidence implicates cellular stress mechanisms in neuropsychiatric disorders associated with prenatal stress including affective disorders, schizophrenia, and child-onset psychiatric disorders. Heat shock factors and oxidative stress also have links with the mechanisms involved in other kinds of prenatal stress including external exposures such as environmental toxicants and internal disruptions such as preeclampsia. Integrative understanding of developmental neurobiology with these cellular and physiological mechanisms is necessary to reduce risks and promote healthy brain development.

Neuroprotective and restorative effects of the brain-derived neurotrophic factor in retinal diseases

Brain-derived neurotrophic factor (BDNF) is a neurotrophin proposed to be implicated in ameliorating the course of some neurodegenerative disorders. Given the fact that retina is considered as an out-pouching of the central nervous system, its related diseases have long been suggested to receive protective influence from this signaling molecule. The role of BDNF in retinal neurorestoration, neuroprotection and oxidative stress has extensively been tested over the past two decades. Nonetheless, almost the entire related literature root in animal studies and clinical research on this topic is lacking. Although much of the evidence have validated the protective properties of BDNF against various retinal cell diseases, bringing such insights into clinical context would depend on further well-designed research. The present review is an attempt to categorize and discuss the available evidence with regard to the BDNF and retinal diseases.

Targeted delivery of brain-derived neurotrophic factor for the treatment of blindness and deafness

Neurodegenerative causes of blindness and deafness possess a major challenge in their clinical management as proper treatment guidelines have not yet been found. Brain-derived neurotrophic factor (BDNF) has been established as a promising therapy against neurodegenerative disorders including hearing and visual loss. Unfortunately, the blood–retinal barrier and blood–cochlear barrier, which have a comparable structure to the blood–brain barrier prevent molecules of larger sizes (such as BDNF) from exiting the circulation and reaching the targeted cells. Anatomical features of the eye and ear allow use of local administration, bypassing histo-hematic barriers. This paper focuses on highlighting a variety of strategies proposed for the local administration of the BDNF, like direct delivery, viral gene therapy, and cell-based therapy, which have been shown to successfully improve development, survival, and function of spiral and retinal ganglion cells. The similarities and controversies for BDNF treatment of posterior eye diseases and inner ear diseases have been analyzed and compared. In this review, we also focus on the possibility of translation of this knowledge into clinical practice. And finally, we suggest that using nanoparticulate drug-delivery systems may substantially contribute to the development of clinically viable techniques for BDNF delivery into the cochlea or posterior eye segment, which, ultimately, can lead to a long-term or permanent rescue of auditory and optic neurons from degeneration.

Expression of inducible heat shock proteins Hsp27 and Hsp70 in the visual pathway of rats subjected to various models of retinal ganglion cell injury

Inducible heat shock proteins (Hsps) are upregulated in the central nervous system in response to a wide variety of injuries. Surprisingly, however, no coherent picture has emerged regarding the magnitude, duration and cellular distribution of inducible Hsps in the visual system following injury to retinal ganglion cells (RGCs). The current study sought, therefore, to achieve the following two objectives. The first aim of this study was to systematically characterise the patterns of Hsp27 and −70 expression in the retina and optic nerve in four discrete models of retinal ganglion cell (RGC) degeneration: axonal injury (ON crush), somato-dendritic injury (NMDA-induced excitotoxicity), chronic hypoperfusion (bilateral occlusion of the carotid arteris) and experimental glaucoma. The second aim was to document Hsp27 and −70 expression in the optic tract, the subcortical retinorecipient areas of the brain, and the visual cortex during Wallerian degeneration of RGC axons. Hsp27 was robustly upregulated in the retina in each injury paradigm, with the chronic models, 2VO and experimental glaucoma, displaying a more persistent Hsp27 transcriptional response than the acute models. Hsp27 expression was always associated with astrocytes and with a subset of RGCs in each of the models excluding NMDA. Hsp27 was present within astrocytes of the optic nerve/optic tract in control rats. During Wallerian degeneration, Hsp27 was upregulated in the optic nerve/optic tract and expressed de novo by astrocytes in the lateral geniculate nucleus and the stratum opticum of the superior colliculus. Conversely, the results of our study indicate Hsp70 was minimally induced in any of the models of injury, either in the retina, or in the optic nerve/optic tract, or in the subcortical, retinorecipient areas of the brain. The findings of the present study augment our understanding of the involvement of Hsp27 and Hsp70 in the response of the visual system to RGC degeneration.

Mechanisms of secondary degeneration after partial optic nerve transection

Secondary degeneration occurs commonly in the central nervous system after traumatic injuries and following acute and chronic diseases, including glaucoma. A constellation of mechanisms have been shown to be associated with secondary degeneration including apoptosis, necrosis, autophagy, oxidative stress, excitotoxicity, derangements in ionic homeostasis and calcium influx. Glial cells, such as microglia, astrocytes and oligodendrocytes, have also been demonstrated to take part in the process of secondary injury. Partial optic nerve transection is a useful model which was established about 13 years ago. The merit of this model compared with other optic nerve injury models used for glaucoma study, including complete optic nerve transection model and optic nerve crush model, is the possibility to separate primary degeneration from secondary degeneration in location. Therefore, it provides a good tool for the study of secondary degeneration. This review will focus on the research progress of the mechanisms of secondary degeneration using partial optic nerve transection model.

Hepatocyte growth factor promotes long-term survival and axonal regeneration of retinal ganglion cells after optic nerve injury: comparison with CNTF and BDNF

AIMS

Different trophic factors are known to promote retinal ganglion cell survival and regeneration, but each had their own limitations. We report that hepatocyte growth factor (HGF) confers distinct advantages in supporting ganglion cell survival and axonal regeneration, when compared to two well-established trophic factors ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF).

METHODS

Ganglion cells in adult hamster were injured by cutting the optic nerve. HGF, CNTF, or BDNF was injected at different dosages intravitreally after injury. Ganglion cell survival was quantified at 7, 14, or 28 days postinjury. Peripheral nerve (PN) grafting to the cut optic nerve of the growth factor-injected eye was performed either immediately after injury or delayed until 7 days post-injury. Expression of heat-shock protein 27 and changes in microglia numbers were quantified in different growth factor groups. The cellular distribution of c-Met in the retina was examined by anti-c-Met immunostaining.

RESULTS

Hepatocyte Growth Factor (HGF) was equally potent as BDNF in promoting short-term survival (up to 14 days post-injury) and also supported survival at 28 days post-injury when ganglion cells treated by CNTF or BDNF failed to be sustained. When grafting was performed without delay, HGF stimulated twice the number of axons to regenerate compared with control but was less potent than CNTF. However, in PN grafting delayed for 7 days after optic nerve injury, HGF maintained a better propensity of ganglion cells to regenerate than CNTF. Unlike CNTF, HGF application did not increase HSP27 expression in ganglion cells. Microglia proliferation was prolonged in HGF-treated retinas compared with CNTF or BDNF. C-Met was localized to both ganglion cells and Muller cells, suggesting HGF could be neuroprotective via interacting with both neurons and glia.

CONCLUSION

Compared with CNTF or BDNF, HGF is advantageous in sustaining long-term ganglion cell survival and their propensity to respond to favorable stimuli.

Exploiting the diversity of the heat-shock protein family for primary and secondary tauopathy therapeutics

The heat shock protein (Hsp) family is an evolutionarily conserved system that is charged with preventing unfolded or misfolded proteins in the cell from aggregating. In Alzheimer’s disease, extracellular accumulation of the amyloid β peptide (Aβ) and intracellular aggregation of the microtubule associated protein tau may result from mechanisms involving chaperone proteins like the Hsps. Due to the ability of Hsps to regulate aberrantly accumulating proteins like Aβ and tau, therapeutic strategies are emerging that target this family of chaperones to modulate their pathobiology. This article focuses on the use of Hsp-based therapeutics for treating primary and secondary tauopathies like Alzheimer’s disease. It will particularly focus on the pharmacological targeting of the Hsp70/90 system and the value of manipulating Hsp27 for treating Alzheimer’s disease.

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

Modulating expression of brain heat shock proteins by estrogen in ovariectomized mice model of aging

Heat shock proteins (HSPs) serve as molecular chaperones and endogenous cytoprotective factors. Two of the well-studied HSPs, HSP70, and HSP27 can be significantly induced in many areas of brain by a variety of stressors. A decrease in expression of brain HSPs has been documented in aged brain. Estrogen is well known as a neuroprotective hormone, and it has been reported that estrogen can regulate HSP70 and HSP27 expression in neuronal cells. In this study, the relationship between estrogen and heat stress-induced brain HSPs expression in young and aged ovariectomized (OVX) mice was investigated. Our results show that heat stress-induced levels of HSP70 proteins and mRNA transcripts was significantly lower in brain of aged (12 month) OVX mice, compared with young (2 month) OVX mice group. Estrogen supplementation (17beta-estradiol 0.5mg/kg for 7 days) restored heat stress-induced brain HSP70 expression and attenuated heat stress-induced brain DNA fragmentation, caspase 3 activation and mitochondrial leakage of cytochrome c and AIF in OVX mice. These results suggest that estrogen deficiency during aging down-regulates heat stress-induced brain HSP70 expression, which reveals a previously unknown link between estrogen deficiency and stress response elements.

Involvement of acidic fibroblast growth factor in spinal cord injury repair processes revealed by a proteomics approach

Acidic fibroblast growth factor (aFGF; also known as FGF-1) is a potent neurotrophic factor that affects neuronal survival in the injured spinal cord. However, the pathological changes that occur with spinal cord injury (SCI) and the attribution to aFGF of a neuroprotective effect during SCI are still elusive. In this study, we demonstrated that rat SCI, when treated with aFGF, showed significant functional recovery as indicated by the Basso, Beattie, and Bresnahan locomotor rating scale and the combined behavior score (p < 0.01-0.001). Furthermore proteomics and bioinformatics approaches were adapted to investigate changes in the global protein profile of the damaged spinal cord tissue when experimental rats were treated either with or without aFGF at 24 h after injury. We found that 51 protein spots, resolvable by two-dimensional PAGE, had significant differential expression. Using hierarchical clustering analysis, these proteins were categorized into five major expression patterns. Noticeably proteins involved in the process of secondary injury, such as astrocyte activation (glial fibrillary acidic protein), inflammation (S100B), and scar formation (keratan sulfate proteoglycan lumican), which lead to the blocking of injured spinal cord regeneration, were down-regulated in the contusive spinal cord after treatment with aFGF. We propose that aFGF might initiate a series of biological processes to prevent or attenuate secondary injury and that this, in turn, leads to an improvement in functional recovery. Moreover the quantitative expression level of these proteins was verified by quantitative real time PCR. Furthermore we identified various potential neuroprotective protein factors that are induced by aFGF and may be involved in the spinal cord repair processes of SCI rats. Thus, our results could have a remarkable impact on clinical developments in the area of spinal cord injury therapy.

Changes of central visual receptive fields in experimental glaucoma

Retinal ganglion cell apoptotic death in experimental glaucoma is protracted over several months and it leads to the visual dysfunction. In the rat with increased intraocular pressure (IOP), the lack of visual scotoma was observed where visual field was determined electrophysiologically on the contralateral optic tectum in the early stages of the disease. Increases in the sizes of receptive fields on the periphery represented early stage of glaucomatous dysfunction. The relationship of duration and magnitude of IOP elevation had a significant correlation between percentages of receptive field sizes in the tectum. Large increases in receptive field sizes noted in the glaucomatous retinal terminal areas suggest the ability of the remaining retinal axons to compete and compensate for the loss of retinal axons. This compensatory adaptation leads to the degradation of the visual acuity and visual thresholds when measured psychophysically.

The changes in neurotrophic properties of the peripheral nerves extracts following blocking of BDNF activity

OBJECTIVES

Retinal ganglion cells (RGCs) of adult rats are unable to regenerate their axons after optic nerve injury and soon after they enter the pathway of apoptosis. They may, however, survive and regenerate new axons in response to application of specific peripheral nerve extracts that presumably contain a range of neurotrophic substances. One of the recognized substances of proven neurotrophic activity is brain-derived neurotrophic factor (BDNF). We have investigated whether blocking the BDNF activity in post-microsomal fractions obtained from 7 day pre-degenerated peripheral nerves would affect its neurotrophic properties towards RGCs after optic nerve transection in adult rats.

METHODS

Autologous connective tissue chambers sutured to the distal end of transected optic nerve served as active substances containers. Surviving RGCs were visualized using Dil. The number of myelinated outgrowing fibers within the chambers was evaluated in histologic sections.

RESULTS

BDNF and 7 day pre-degenerated nerve extracts, and also extracts with blocked BDNF activity, enhanced RGC fibers outgrowth. The regeneration was significantly weaker in the control group. Blocking the BDNF activity in the 7 day pre-degenerated peripheral nerve extract reduced its neurotrophic effects but the differences were insignificant in comparison with non-blocked extracts.

DISCUSSION

The regeneration intensities in groups receiving 7 day pre-degenerated peripheral nerve extracts (PD7) and BDNF were comparable. The number of surviving cells was higher in the PD7 group and there were more regenerating fibers in the BDNF group, which may be explained by the strong BDNF effect on axonal collateralization and sprouting.

Region-specific transcriptional changes following the three antidepressant treatments electro convulsive therapy, sleep deprivation and fluoxetine

The significant proportion of depressed patients that are resistant to monoaminergic drug therapy and the slow onset of therapeutic effects of the selective serotonin reuptake inhibitors (SSRIs)/serotonin/noradrenaline reuptake inhibitors (SNRIs) are two major reasons for the sustained search for new antidepressants. In an attempt to identify common underlying mechanisms for fast- and slow-acting antidepressant modalities, we have examined the transcriptional changes in seven different brain regions of the rat brain induced by three clinically effective antidepressant treatments: electro convulsive therapy (ECT), sleep deprivation (SD), and fluoxetine (FLX), the most commonly used slow-onset antidepressant. Each of these antidepressant treatments was applied with the same regimen known to have clinical efficacy: 2 days of ECT (four sessions per day), 24 h of SD, and 14 days of daily treatment of FLX, respectively. Transcriptional changes were evaluated on RNA extracted from seven different brain regions using the Affymetrix rat genome microarray 230 2.0. The gene chip data were validated using in situ hybridization or autoradiography for selected genes. The major findings of the study are: 1. The transcriptional changes induced by SD, ECT and SSRI display a regionally specific distribution distinct to each treatment. 2. The fast-onset, short-lived antidepressant treatments ECT and SD evoked transcriptional changes primarily in the catecholaminergic system, whereas the slow-onset antidepressant FLX treatment evoked transcriptional changes in the serotonergic system. 3. ECT and SD affect in a similar manner the same brain regions, primarily the locus coeruleus, whereas the effects of FLX were primarily in the dorsal raphe and hypothalamus, suggesting that both different regions and pathways account for fast onset but short lasting effects as compared to slow-onset but long-lasting effects. However, the similarity between effects of ECT and SD is somewhat confounded by the fact that the two treatments appear to regulate a number of transcripts in an opposite manner. 4. Multiple transcripts (e.g. brain-derived neurotrophic factor (BDNF), serum/glucocorticoid-regulated kinase (Sgk1)), whose level was reported to be affected by antidepressants or behavioral manipulations, were also found to be regulated by the treatments used in the present study. Several novel findings of transcriptional regulation upon one, two or all three treatments were made, for the latter we highlight homer, erg2, HSP27, the proto oncogene ret, sulfotransferase family 1A (Sult1a1), glycerol 3-phosphate dehydrogenase (GPD3), the orphan receptor G protein-coupled receptor 88 (GPR88) and a large number of expressed sequence tags (ESTs). 5. Transcripts encoding proteins involved in synaptic plasticity in the hippocampus were strongly affected by ECT and SD, but not by FLX. The novel transcripts, concomitantly regulated by several antidepressant treatments, may represent novel targets for fast onset, long-duration antidepressants.

Target-derived neurotrophins may influence the survival of adult retinal ganglion cells when local neurotrophic support is disrupted: Implications for glaucoma

Following target innervation, developing and neonatal retinal ganglion cells (RGCs) depend on neurotrophic factors from their target tissue for survival. This dependence is reduced for adult RGCs which rely primarily on trophic support from their local environment; however, some findings indicate that target tissue may play a role in the long-term survival of RGCs. We propose that a deficiency in neurotrophic factors from the target tissue may influence the survival of RGCs when local neurotrophic support is disrupted. Furthermore, we propose that this hypothesis may explain, at least in part, the progressive loss of RGCs in optic neuropathies such as glaucoma. Neurotrophic factors are present in the adult superior colliculus and they are trafficked to the retina; however, removal or lesioning of the adult target tissue results in little or no RGC loss for up to several months. In vitro, adult RGCs will survive when maintained by co-culturing these neurons with their target tissue. As well, the timing and pattern of adult RGC loss is consistent with that seen in glaucoma and in reports of delayed RGC loss following target-removal. Our hypothesis can be tested by selectively disrupting local neurotrophic support and evaluating RGC survival when target-derived neurotrophic support is maintained and when it is disrupted. Specifically, intravitreal injection of blocking antibodies could be used to disrupt local neurotrophic signaling, while aspiration of the superior colliculus will eliminate retrograde transport from the primary target tissue in rodents. The results of these experiments would provide valuable information concerning the influence of target-derived neurotrophic support when local neurotrophin signaling is disrupted. Specifically, this research could verify whether deficiencies in target-derived neurotrophic support play a role in RGC loss during glaucoma. A further understanding of this mechanism may lead to the development of effective neuroprotective strategies for treating glaucoma.

Enriched environment during adolescence changes brain-derived neurotrophic factor and TrkB levels in the rat visual system but does not offer neuroprotection to retinal ganglion cells following axotomy

The purpose of the present experiment was to characterize changes in TrkB signaling in the rat visual system resulting from exposure to enriched environment. Female Sprague-Dawley rats were placed in enriched or impoverished conditions for 1, 7 or 28 days. Levels of BDNF protein and its predominant receptor TrkB were examined in the retina, superior colliculus and visual cortex. In the retina, 1 day of enrichment increased full-length TrkB and after 28 days increased BDNF. In the superior colliculus, enrichment for 7 days reduced full-length TrkB and after 28 days increased BDNF and full-length TrkB. One day of enrichment significantly increased BDNF, reduced full-length TrkB and increased truncated TrkB in the visual cortex. Consequently, we further investigated whether exposure to enriched environment and the subsequent changes in BDNF and TrkB translates into a neuroprotective effect on retinal ganglion cells (RGCs) following transection of the optic nerve. Although exogenous intraocular application of BDNF provides neuroprotection to RGCs after axotomy, the endogenous increase in BDNF in the retina after 28 days of enrichment had no effect on RGC survival. While enriched housing conditions offer a model of non-invasive rehabilitation treatment for injury and modulates changes in BDNF and TrkB levels, these molecular changes did not translate into a neuroprotective effect on RGCs following transection of the optic nerve.

Tyrosine kinase receptor immunoreactivity in trigeminal mesencephalic and motor neurons following transection of masseteric nerve of the rat

Neurotrophins are known to promote survival after neural injury. To determine the relative importance of tyrosine kinase receptors on the survival of axotomized trigeminal nuclear neurons, we examined the temporal expression profile of tyrosine kinase A, tyrosine kinase B and tyrosine kinase C receptors in the mesencephalic trigeminal nucleus and the motor trigeminal nucleus following transection of the masseteric nerve in rats. Axotomized neurons in these nuclei were retrogradely identified with FluoroGold. We found increase in tyrosine kinase A-immunoreactive mesencephalic trigeminal nucleus neurons in the second week after axotomy but no change in the number of tyrosine kinase A-immunoreactive motor trigeminal nucleus neurons. There was no change in the number of tyrosine kinase B-immunoreactive mesencephalic trigeminal nucleus neurons but the significant increase of tyrosine kinase B-immunoreactive motor trigeminal nucleus neurons throughout the period of observation (3 weeks) peaked at approximately 1 week after axotomy. There was no alteration in the number of tyrosine kinase C-immunoreactive mesencephalic trigeminal nucleus neurons but significant increase in tyrosine kinase C-immunoreactive motor trigeminal nucleus neurons observable by 4 days post-axotomy was followed by decline to levels lower than the control in 2 weeks. Temporal changes in the expression of individual tyrosine kinase receptors in mesencephalic trigeminal nucleus and motor trigeminal nucleus neurons following transection of the masseteric nerve suggest differential contribution of tyrosine kinase-specific neurotrophins to the survival of these neurons after axotomy.

Activation of the Extracellular Signal-Regulated Kinase 1/2 Pathway by AAV Gene Transfer Protects Retinal Ganglion Cells in Glaucoma

Glaucoma is the second leading cause of blindness in the world. Loss of vision in glaucomatous optic neuropathy is caused by the selective degeneration of retinal ganglion cells (RGCs). Ocular hypertension is a major risk factor in glaucoma, but visual field defects continue to progress in some patients despite the use of drugs that lower intraocular pressure. At present, there are no effective neuroprotective strategies for the treatment of this disease. The extracellular signal-regulated kinase (Erk) 1/2 pathway is an evolutionarily conserved mechanism used by several peptide factors to promote cell survival. Here we tested if selective activation of Erk1/2 protected RGCs in a rat model of experimental glaucoma. We used recombinant adeno-associated virus to transduce RGCs with genes encoding constitutively active or wild-type MEK1 (approved gene symbol MAP2K1), the upstream activator of Erk1/2. MEK1 gene transfer into RGCs markedly increased neuronal survival: 1366 +/- 70 RGCs/mm(2) (mean +/- SEM) were alive in the dorsal retina at 5 weeks after ocular hypertension surgery, a time when only 680 +/- 86 RGCs/mm(2) of these neurons remained in control eyes. We conclude that the Erk1/2 pathway plays a key role in the protection of RGCs from ocular hypertensive damage. This study identifies a novel gene therapy strategy in which selective activation of the Erk1/2 signaling pathway effectively slows cell death in glaucoma.

Effect of exogenous administration of nerve growth factor in the retina of rats with inherited retinitis pigmentosa

NGF is implicated in retinal damage regression. To study whether this is a direct effect or an effect mediated by NGF on other endogenous biological mediators, we investigated the effect of exogenous administration of NGF in RCS rats affected by retinitis pigmentosa. We found that NGF administration exerts a rescue effect on photoreceptors in this animal model. NGF injection enhances brain-derived neurotrophic factor, beta-fibroblast growth factor, transforming growth factor-beta, vascular endothelial factor and neuropeptide-Y. This suggests that NGF has an effect on RCS rat retina, probably also through the stimulation of other biological mediators produced and released in the retina.

Expression of Hsp27 in retinal ganglion cells of the rat during postnatal development

The small heat shock protein Hsp27 has been shown to protect neurons from apoptosis. We have recently shown the expression of Hsp27 in a subset of injured adult retinal ganglion cells (RGCs), a response that is muted by the administration of brain-derived neurotrophic factor. This work has suggested a role for Hsp27 in the long-term survival of RGCs following injury. The purpose of this study was to investigate the expression of Hsp27 during postnatal retinal development, based on Hsp27's role as a neuronal survival factor and on its up-regulation in the adult injured retina. Expression of Hsp27 in the developing retina was examined at various times postnatally (between P0 and P24) by using immunohistochemical techniques. We report that Hsp27 expression peaks in the ganglion cell layer between P6 and P12 and is not detected at earlier (P0-P3) or later (P15-P24) times. Double labeling of the Hsp27-positive cells with Fluorogold applied to the superior colliculus confirmed that Hsp27-positive cells in the ganglion cell layer are RGCs. We have shown developmentally regulated expression of Hsp27 in RGCs of the postnatal rat. The retinal expression of Hsp27 correlates temporally with innervation of the tectum by late-born RGCs and with onset of spontaneous retinotectal activity. We propose that the expression of Hsp27 may play an important role in retinal development during a critical period of RGC functional connectivity with the superior colliculus.