Glucocorticoid and progesterone mechanisms in photoreceptor survival.

Death of retinal photoreceptors is the basis of prevalent blinding diseases. Since steroids might have a therapeutic role in retinal degenerations, we compared the protective effects of dexamethasone and progesterone on photoreceptor death induced by mifepristone and light exposure. Therefore, we studied the effective protection doses for each steroid in the two models. In addition, we analyzed changes in the levels of pro- and antiapoptotic molecules, glucocorticoid receptors α and ß (GRα and GRß), and rhodopsin under conditions of successful protection and photoreceptor survival. Mifepristone and light exposure selectively damaged photoreceptors. In light exposed retinas, photoreceptors mainly disappeared in the dorsotemporal region, while mifepristone produced a uniform damage. Dexamethasone and progesterone, at the same dose of 4 mg/kg/day for 2 days, preserved over 88% photoreceptor nuclei in both models. Assessment of cell death regulators showed that, in control retinas, both steroids activated BCL-XL, a prosurvival molecule, and decreased BID, a proapoptotic regulator. After steroid treatment of damaged retinas, BCL-XL, BCL2 and BAX showed characteristic patterns depending on the use of dexamethasone or progesterone on mifepristone or light exposed retinas. By contrast, BID decreased with any injury-steroid combination. Changes in GRα or GRß levels did not correlate with survival but were consistent with a mechanism of ligand induced downregulation of receptor expression. GRß might be upregulated by progesterone. Both dexamethasone and progesterone increased retinal rhodopsin stores, suggesting a link between photoreceptor protection and transduction pathways. Results show that dexamethasone and progesterone induced comparable but not identical protection responses in each model.

Early ciliary and prominin-1 dysfunctions precede neurogenesis impairment in a mouse model of type 2 diabetes.

Diabetes mellitus (DM) is reaching epidemic conditions worldwide and increases the risk for cognition impairment and dementia. Here, we postulated that progenitors in adult neurogenic niches might be particularly vulnerable. Therefore, we evaluated the different components of the mouse subventricular zone (SVZ) during the first week after chemical induction of type 1 and type 2 diabetes-like (T1DM and T2DM) conditions. Surprisingly, only T2DM mice showed SVZ damage. The initial lesions were localized to ependymal cilia, which appeared disorientated and clumped together. In addition, they showed delocalization of the ciliary membrane protein prominin-1. Impairment of neuroprogenitor proliferation, neurogenic marker abnormalities and ectopic migration of neuroblasts were found at a later stage. To our knowledge, our data describe for the first time such an early impact of T2DM on the SVZ. This is consistent with clinical data indicating that brain damage in T2DM patients differs from that in T1DM patients.

Photo-damage, photo-protection and age-related macular degeneration.

Age-related macular degeneration (AMD) is a degenerative retinal disease that causes blindness in people 60-65 years and older, with the highest prevalence appearing in people 90 years-old or more. Epidemiological estimates indicate that the number of cases is increasing, and will almost double in the next 20 years. Preventive measures require precise etiological knowledge. This is quite difficult, since AMD is a multifactorial condition with intricate relationships between causes and risk factors. In this review, we describe the impact of light on the structure and physiology of the retina and the pigment epithelium, taking into account the continuous exposure to natural and artificial light sources along the life of an individual. A large body of experimental evidence demonstrates the toxic effects of some lighting conditions on the retina and the pigment epithelium, and consensus exists about the importance of photo-oxidation phenomena in the causality chain between light and retinal damage. Here, we analyzed the transmission of light to the retina, and compared the aging human macula in healthy and diseased retinas, as shown by histology and non-invasive imaging systems. Finally, we have compared the putative retinal photo-sensitive molecular structures that might be involved in the genesis of AMD. The relationship between these compounds and retinal damage supports the hypothesis of light as an important initiating cause of AMD.

Sitagliptin protects proliferation of neural progenitor cells in diabetic mice.

Sitagliptin (SIT) is a dipeptidyl peptidase-4 (DPP-4) inhibitor that enhances the effects of incretin hormones, such as Glucose-dependent Insulinotropic Peptide (also known as Gastric Inhibitory Polypeptide, GIP) and Glucagon-Like Peptide 1 (GLP-1). We have now evaluated the effect of SIT on proliferation of neural progenitors in diabetic mice. A condition resembling the non-obese type 2 diabetes mellitus (D2) was achieved by a combination of streptozotocin and nicotinamide (NA-STZ), whereas a type 1-like disease (D1) was provoked by STZ without NA. Non-diabetic mice received vehicle injections. Cell proliferation was estimated by bromodeoxyuridine (BrdU) incorporation in two different regions of the subventricular zone (SVZ), the largest reserve of neural stem cells in the adult brain. SIT treatment did not modify the high fasting blood glucose (BG) levels and intraperitoneal glucose tolerance test (IPGTT) of D1 mice. By contrast, in D2 mice, SIT treatment significantly reduced BG and IPGTT. Both D1 and D2 mice showed a substantial reduction of BrdU labeling in the SVZ. Remarkably, SIT treatment improved BrdU labeling in both conditions. Our findings suggest that SIT would protect proliferation of neural progenitor cells even in the presence of non-controlled diabetic alterations.

Excitotoxic spinal damage induced by kainic acid impairs locomotion, alters nociception, and reduces CREB nuclear translocation.

Our previous in vitro studies showed that excitotoxicity evoked by glutamate analogue kainate (KA) significantly decreased the number of rat spinal neurons and triggered high release of glutamate leading to locomotor network block. Our current objective was to assess the role of CREB as a predictive marker of damage following chemically-induced spinal cord injury by using in vivo and in vitro models. Thus, in vivo excitotoxicity in Balb/c adult mice was induced by KA intraspinal injection, while in vitro spinal cord excitotoxicity was produced by bath-applied KA. KA application evoked significant neuronal loss, deterioration in hindlimb motor coordination and thermal allodynia. In addition, immunohistochemical analysis showed that KA application resulted in decreased number of CREB positive nuclei in the ventral horn and in dorsal layers III-IV. Our data suggests that excitotoxic-induced neuronal loss may be potentially predicted by altered CREB nuclear translocation.

Ilex paraguariensis Extracts Prevent Oxidative Damage in a Mouse Model of Age-Related Macular Degeneration.

Age-related macular degeneration (AMD), a chronic disease of the retina, leads to severe visual loss. AMD affects the retinal pigment epithelium (RPE) and the visual cells (photoreceptors). RPE failure, the first step of this disease, is associated with oxidative stress. Since antioxidants can slow down AMD progression, the intake of foods and drinks rich in antioxidant compounds may reduce retinal damage. Ilex paraguariensis (yerba mate, YM) extracts reduce oxidative damage of RPE cells in vitro as shown in previous study. Here, the effects of YM drinking on RPE and photoreceptor survival after oxidative damage with sodium iodate (NaIO3; SI) in a murine AMD model are described. Funduscopy and histology show that YM treatment prevents RPE and photoreceptor damage. YM also increases the expression of NRF2, the master antioxidant gene, and its effectors HO-1 and SOD2. In mice receiving YM and SI, the antioxidant response is larger than in mice receiving YM or SI alone. The YM drink also increases expression of RPE65, a gene that is involved in the functionality and survival of photoreceptors and RPE cells. The results suggest YM can play an important role in the prevention of retinal damage associated with oxidative stress, such as AMD.

Controlling retinal pigment epithelium injury after experimental detachment of the retina.

PURPOSE: Damage induced by detachment of the neural retina and the retinal pigment epithelium (RPE) can be reduced by dark adaptation. The authors evaluated the influence of the duration of dark adaptation, time of day, and modification of the melatonin-dopamine pathway on acute RPE lesions induced by mechanical detachment. METHODS: BALB/c mice were studied at different times of day and different periods of dark adaptation. Some mice were treated with melatonin or sulpiride, a D2 dopamine receptor antagonist. Enucleated eyes and different saline solutions were used in experiments ex vivo. Retinal detachments in vivo were made by subretinal injections of hyaluronic acid. RPE cell damage was quantitatively evaluated with a dye exclusion procedure, and their viability was tested by preservation of tight junctions in culture. Lectin histochemistry was used to examine the interphotoreceptor matrix (IPM). RESULTS: Significant propidium iodide (PI) incorporation in RPE cells was detected after ex vivo separation during daytime, but it was very low when detachment took place at night after 24 to 48 hours of dark adaptation. PI exclusion was achieved during daytime after a single hour of dark adaptation when mice were pretreated with melatonin or sulpiride. Reduction of RPE cell damage was accompanied by decreased lectin binding to cone sheaths. CONCLUSIONS: A combination of time of day and length of dark adaptation decreased damage induced by detachment of the retina ex vivo and in vivo. Melatonin or sulpiride could replace these environmental factors. Therefore, melatonin and dopamine pathways might be involved in the control of IPM properties and retina/RPE interactions.

Endothelin receptors in light-induced retinal degeneration.

Excessive light exposure leads to retinal degeneration in albino animals and exacerbates the rate of photoreceptor apoptosis in several retinal diseases. In previous studies we have described the presence of endothelin-1 (ET-1) and its receptors (ET-A and ET-B) in different sites of the mouse retina, including the retinal pigment epithelium, the outer plexiform layer (OPL), astrocytes, the ganglion cell layer (GCL), and vascular endothelia. After light-induced degeneration of photoreceptors, endothelinergic structures disappear from the OPL, but ET-1 and ET-B immunoreactivities increase in astrocytes. Here, we present novel observations about the course of light-induced retinal degeneration in BALB-c mice exposed to 1500 lux during 4 days with or without treatment with tezosentan, a mixed endothelinergic antagonist. Retinal whole mounts were immunostained with anticleaved caspase-3 (CC-3) serum to identify apoptotic photoreceptor cells within the outer nuclear layer (ONL). Glial activation was measured as glial fibrillary acidic protein (GFAP) immunoreactivity in retinal whole mounts and in Western blots from retinal extracts. Tezosentan treatment significantly reduced both the number of CC3-immunoreactive cells and GFAP levels, suggesting that inhibition of endothelinergic receptors could play a role in photoreceptor survival. Using confocal double immunofluorescence, we have observed that ET-A seems to be localized in bipolar cell dendrites, whereas ET-B is localized in horizontal cells. Our observations suggest the existence of an endothelinergic mechanism modulating synaptic transmission in the OPL. This mechanism could perhaps explain the effects of tezosentan treatment on photoreceptor survival.

Inhibition of salivary secretion by activation of cannabinoid receptors.

It is known that marijuana use decreases saliva secretion. Therefore, we hypothesized that cannabinoid receptors (CBs) are located in salivary glands to mediate that effect. In these experiments, we used the submandibular gland (SMG) of male rats, which is one of the major salivary glands. Mammalian tissues contain at least two types of CBs, CB1 and CB2, mainly located in the nervous system and peripheral tissues, respectively. Both receptors are coupled to Gi protein and respond by inhibiting the activity of adenylyl cyclase. We demonstrated that both CB1 and CB2 are present in the SMG, each showing specific localizations. The best-known endocannabinoid is anandamide (AEA), which binds with high affinity to CB1 and CB2. We showed that AEA markedly reduced forskolin-induced increase of cAMP content in vitro. This effect was blocked by AM251 and AM630 (CB1 and CB2 antagonists, respectively), indicating that both receptors are implicated in SMG physiology. In addition, we showed that AEA injected intraglandularly to anesthetized rats inhibited norepinephrine (NE)- and methacholine (MC)-stimulated saliva secretion in vivo and that both AM251 or AM630 prevented the inhibitory action of AEA. Also, the intraglandular injection of AM251 increased saliva secretion induced by lower doses of NE or MC. This increase was synergized after coinjection with AM630. Therefore, we concluded that AEA decreases saliva secretion in the SMG acting through CB1 and CB2 receptors.

Oxidative stress-induced premature senescence dysregulates VEGF and CFH expression in retinal pigment epithelial cells: Implications for Age-related Macular Degeneration.

Oxidative stress has a critical role in the pathogenesis of Age-related Macular Degeneration (AMD), a multifactorial disease that includes age, gene variants of complement regulatory proteins and smoking as the main risk factors. Stress-induced premature cellular senescence (SIPS) is postulated to contribute to this condition. In this study, we hypothesized that oxidative damage, promoted by endogenous or exogenous sources, could elicit a senescence response in RPE cells, which would in turn dysregulate the expression of major players in AMD pathogenic mechanisms. We showed that exposure of a human RPE cell line (ARPE-19) to a cigarette smoke concentrate (CSC), not only enhanced Reactive Oxygen Species (ROS) levels, but also induced 8-Hydroxydeoxyguanosine-immunoreactive (8-OHdG) DNA lesions and phosphorylated-Histone 2AX-immunoreactive (p-H2AX) nuclear foci. CSC-nuclear damage was followed by premature senescence as shown by positive senescence associated-ß-galactosidase (SA-ß-Gal) staining, and p16(INK4a) and p21(Waf-Cip1) protein upregulation. N-acetylcysteine (NAC) treatment, a ROS scavenger, decreased senescence markers, thus supporting the role of oxidative damage in CSC-induced senescence activation. ARPE-19 senescent cultures were also established by exposure to hydrogen peroxide (H2O2), which is an endogenous stress source produced in the retina under photo-oxidation conditions. Senescent cells upregulated the proinflammatory cytokines IL-6 and IL-8, the main markers of the senescence-associated secretory phenotype (SASP). Most important, we show for the first time that senescent ARPE-19 cells upregulated vascular endothelial growth factor (VEGF) and simultaneously downregulated complement factor H (CFH) expression. Since both phenomena are involved in AMD pathogenesis, our results support the hypothesis that SIPS could be a principal player in the induction and progression of AMD. Moreover, they would also explain the striking association of this disease with cigarette smoking.

Peptidergic innervation of blood vessels and interstitial cells in the testis of the cat.

We studied the innervation of the cat testis using a panel of antisera against the following neuronal markers: protein gene product 9.5 (PGP), neuropeptide Y, C-terminal peptide of neuropeptide Y, galanin, vasoactive intestinal peptide (VIP), calcitonin gene-related peptide, and substance P. Immunoreactivity against PGP, a general neuronal label, demonstrated the arrangement of fibers from the superior spermatic nerve (SSN) in the testicular pedicle and the cephalic testicular pole, and those of the inferior spermatic nerve (ISN) along the vas deferens and the inferior testicular ligament. The testicular parenchyma exhibited a very rich innervation, mainly distributed to blood vessels and Leydig cell nests, but also in close association with seminiferous tubules. Numerous peptidergic fibers were present in the SSN and ISN, albeit in different proportions. Thus, VIP-immunoreactive fibers were almost absent in the SSN, but were the most abundant subpopulation of the ISN. The testicular interstitium contained numerous peptidergic fibers, associated with blood vessels, interstitial Leydig cells, and seminiferous tubules. Similar fibers were related to the rete testis. Parenchymatous VIP-immunoreactive nerves disappeared after bilateral vasectomy. Stimulation of the ISN under experimental conditions was associated with an increase of blood flow, and induced a large release of VIP into the spermatic vein. The extensive and selective distribution of nerve fibers within the cat testicular parenchyma supports the importance of spermatic nerves for testicular function. Furthermore, the differences in the fiber composition of the SSN and ISN can be correlated with their opposing effects on testosterone secretion and testicular blood flow.

Behavior problems in children with specific language impairment.

We studied behavior in a group of children with specific language impairment in its 2 subtypes (expressive and mixed receptive/expressive). After exclusion of other psychiatric conditions, we evaluated 114 children of ages 2 to 7 years using language developmental tests and behavioral screening scales. Behavior problems appeared in 54% of the children. Withdrawn was the most frequently found syndrome in preschool children, whereas anxious/depressed and social problems were the most frequent in older children. The high frequency of behavioral syndromes in children with specific language impairment is remarkable and requires the awareness of primary attendants and specialists. Anxiety, depression, social isolation, and aggressive and rule-breaking behavior can obscure identification of the language impairment. Taking into account this relationship would improve the chances of a timely and appropriate intervention.

Mifepristone, a blocker of glucocorticoid receptors, promotes photoreceptor death.

PURPOSE: Glucocorticoids are best known by their protective effect on retinal photoreceptor damage. However, they could also be involved in photoreceptor homeostasis under basal, nonstressful conditions. Therefore, we aimed to study glucocorticoid-induced changes of survival-related molecules in male mice retinas under standard illumination conditions (12 hours light, ≤ 60 lux/12 h dark). METHODS: Male Balb-c mice were injected with dexamethasone (DEX), a selective glucocorticoid receptor α (GRα) agonist, its antagonist mifepristone (MFP), or both drugs (D+M) at noon. A group of mice was subjected to surgical adrenalectomy (AdrX). Retinas were studied by histology, immunohistochemistry, TUNEL procedure, and Western blotting at different periods after pharmacological or surgical intervention (6 hours, 48 hours, or 7 days). RESULTS: The antiapoptotic molecule Bcl-X(L) significantly increased 6 hours after DEX injection. By contrast, this molecule could no longer be found after MFP injection. At the same time, high levels of cleaved caspase-3 (CC-3) and Bax appeared in retinal extracts, and TUNEL(+) nuclei selectively showed in the outer nuclear layer (ONL). After MFP, retinal extracts also contained phosphorylated histone H2AX (p-H2AX), a marker of DNA breakage and repair. Loss of ONL nuclear rows and decrease of rhodopsin levels were evident 7 days after MFP administration. These changes were minimized when DEX was given together with MFP (D+M). In the absence of MFP, DEX increased Bcl-X(L) in every retinal layer, with a marked intensification in photoreceptor inner segments. Numerous TUNEL(+) nuclei rapidly appeared in the ONL after AdrX. CONCLUSIONS: A single dose of MFP induced selective photoreceptor damage in the absence of other environmental stressors. Because damage was prevented by DEX, and was reproduced by AdrX, our findings suggest that glucocorticoids play a critical role in photoreceptor survival.

Islet cannabinoid receptors: cellular distribution and biological function.

OBJECTIVES: This study aimed to determine the cellular distribution of islet cannabinoid receptors (CBs) and their involvement in the development of metabolic and hormonal changes in rats fed a fructose-rich diet (F). METHODS: In normal rat islets, we determined CBs (immunofluorescence and retrotranscription-polymerase chain reaction) and glucose-stimulated insulin secretion (GSIS) of isolated islets incubated with the CB1 antagonist rimonabant (R) and/or different CBs agonists. In 3-week F-fed rats, we determined the in vivo effect of R on serum glucose, triglyceride, and insulin levels; homeostasis model assessment for insulin resistance, GSIS, and CBs and insulin receptor substrate gene expression levels (real-time polymerase chain reaction). RESULTS: Cannabinoid receptors appeared exclusively in islet α cells. Whereas different CB agonists enhanced GSIS in normal rat islets, R did not affect it. F rats had higher serum triglyceride and insulin levels and homeostasis model assessment for insulin resistance than control rats; these alterations were prevented by R coadministration. Although R did not correct the increased GSIS observed in F islets, it modulated CBs and insulin receptor substrate gene expression. CONCLUSIONS: Islet CBs would exert an important modulatory role in metabolic homeostasis. Administration of R and F affected islet CB expression and prevented the development of F-induced metabolic impairment. Selective islet CB1 blockers could be useful to prevent/treat the alterations induced by the intake of unbalanced/unhealthy diets.

Neural stem cells in the diabetic brain.

Experimental diabetes in rodents rapidly affects the neurogenic niches of the adult brain. Moreover, behavioral disorders suggest that a similar dysfunction of the neurogenic niches most likely affects diabetic and prediabetic patients. Here, we review our present knowledge about adult neural stem cells, the methods used for their study in diabetic models, and the effects of experimental diabetes. Variations in diet and even a short hyperglycemia profoundly change the structure and the proliferative dynamics of the neurogenic niches. Moreover, alterations of diabetic neurogenic niches appear to be associated with diabetic cognitive disorders. Available evidence supports the hypothesis that, in the adult, early changes of the neurogenic niches might enhance development of the diabetic disease.

Endothelinergic signaling during recovery of brain cortical lesions.

OBJECTIVES: Recovery of brain lesions has been associated with increased activation and migration of endogenous neural stem cells, glia, and endothelium. To understand the role of endothelinergic signaling in these phenomena we studied devascularizing lesions of mouse brain cortex. Our specific aims were to: (i) describe the endothelinergic cell phenotypes appearing within the lesions; and (ii) evaluate the effect of endothelinergic blockade on the injured cortex. METHODS: C57BL/6 mice were anesthetized and submitted to devascularization lesions of the right M1 cortical area. A group of mice was daily treated with tezosentan, a dual endothelinergic receptor blocker. Mice were euthanatized 5 days after surgery and the injured area was studied with immunohistochemistry for endothelin, endothelin receptor B, glial fibrillary acidic protein, prominin-1, nestin, and phospho-histone H3. RESULTS: The injured cortex exhibited a large increase of multipolar endothelin(+), endothelin receptor B(+), glial fibrillary acidic protein(+), prominin-1(+), and nestin(+) cells. These markers appeared in different combinations. Tezosentan treatment reduced the perilesional expression of glial fibrillary acidic protein and decreased the number of proliferating cell nuclei displaying phospho-histone H3. DISCUSSION: Our observations suggest that endothelinergic cells surrounding the lesion belong to a mixed population including reactive glia and neural progenitor cells. Findings in tezosentan-treated mice probably reflect a decrease of reactive gliosis with a still unknown effect on neural progenitor cells.

Endothelinergic cells in the subependymal region of mice.

Endothelin (ET) is a small peptide that activates astrocyte proliferation, regulates proliferation and migration of embryonic neural precursor cells and stimulates glioblastoma growth. We found that in mouse brain, ET and its receptor B (ETRB) were highly expressed in the subependymal zone (SEZ), an adult neurogenic niche. Cells with ET immunoreactivity (ET+ cells) selectively appeared along the lateral and dorsal walls of the lateral ventricle. They also appeared in the cingular region of the corpus callosum. Subependymal ET+ cells also displayed prominin (PRO), glial fibrillary acidic protein (GFAP) and ETRB immunoreactivities. ET+ processes traversed the ependymal epithelium and approached the ventricular lumen. Ependymal cells only showed ETRB-ir. A small but consistent number of ET+ cells displayed proliferation markers: 5-bromo-2'-deoxyuridine (BrdU) incorporation, and minichromosome maintenance protein 2 (Mcm2). Cortical injury and G-CSF increased subependymal endothelinergic cells and their proliferation markers. Our findings suggest that ET and ETRB might be associated with regulation of adult neural stem cells and their migration through neurogenic and gliogenic pathways.

Blockade of endothelinergic receptors prevents development of proliferative vitreoretinopathy in mice.

Proliferative vitreoretinopathy (PVR) is characterized by severe glial remodeling. Glial activation and proliferation that occur in brain diseases are modulated by endothelin-1 (ET-1) and its receptor B (ETR-B). Because retinal astrocytes contain ET-1 and express ETR-B, we studied the changes of these molecules in an experimental mouse model of PVR and in human PVR. Both ET-1 and ETR-B immunoreactivities increased in mouse retina after induction of PVR with dispase. Epi- and subretinal outgrowths also displayed these immunoreactivities in both human and experimental PVR. Additionally, myofibroblasts and other membranous cell types showed both ET-1 and ETR-B immunoreactivities. In early stages of experimentally induced PVR, prepro-ET-1 and ETR-B mRNA levels increased in the retina. These mRNA levels also increased after retinal detachment (RD) produced by subretinal injection. Treatment of mice with tezosentan, an antagonist of endothelinergic receptors, reduced the histopathological hallmarks of dispase-induced PVR: retinal folding, epiretinal outgrowth, and gliosis. Our findings in human and in dispase-induced PVR support the involvement of endothelinergic pathways in retinal glial activation and the phenotypic transformations that underlie the growth of membranes in this pathology. Elucidating these pathways further will help to develop pharmacological treatments to prevent PVR. In addition, the presence of ET-1 and ETR-B in human fibrous membranes suggests that similar treatments could be helpful after PVR has been established.