Treatment in vitro of retinal cells with IL-4 increases the survival of retinal ganglion cells: the involvement of BDNF

Interleukin-4 activates divergent cell-intrinsic signals to regulate retinal cell proliferation induced by classical growth factors

In the developing retina, precise coordination of cell proliferation, differentiation, and survival is essential for proper retinal maturation and function. We have previously reported evidence that interleukin-4 (IL-4) plays critical roles in neuronal differentiation and survival during retinal development. However, little is known about the role of IL-4 on retinal cell proliferation. In the current study, we investigated if IL-4 regulates cell proliferation induced by epidermal growth factor (EGF) and by fibroblast growth factor 2 (FGF2) in primary retinal cell cultures obtained from newborn rats. First, we show that EGF and FGF2 act as mitogens for glial cells, increasing proliferation of these cells in the retina. EGF- and FGF2-induced mitogenesis requires activation of distinct cell-intrinsic signals. In retinal cells exposed to FGF2, IL-4 downregulates p53 levels (a protein whose activation induces cell-cycle arrest) and increases mitogenic responsiveness to FGF2 through activation of protein kinase A (PKA) pathway. Conversely, in retinal cells exposed to EGF, IL-4 downregulates cyclin D1 levels (a protein required for cell-cycle progression), upregulates p53 levels, and decreases mitogenic responsiveness to EGF. The inhibitory effect induced by IL-4 on retinal cells exposed to EGF requires activation of Janus kinase 3 (JAK3), but not activation of PKA. Based on previous and current findings, we propose that IL-4 serves as a node of signal divergence, modulating multiple cell-intrinsic signals (e.g., cyclin D1, p53, JAK3, and PKA) and mitogenic responsiveness to cell-extrinsic signals (e.g., FGF2 and EGF) to control cell proliferation, differentiation, and survival during retinal development.

Ouabain-Na+/K+-ATPase Signaling Regulates Retinal Neuroinflammation and ROS Production Preventing Neuronal Death by an Autophagy-Dependent Mechanism Following Optic Nerve Axotomy In Vitro

Ouabain is a classic Na+K+ATPase ligand and it has been described to have neuroprotective effects on neurons and glial cells at nanomolar concentrations. In the present work, the neuroprotective and immunomodulatory potential of ouabain was evaluated in neonatal rat retinal cells using an optic nerve axotomy model in vitro. After axotomy, cultured retinal cells were treated with ouabain (3 nM) at different periods. The levels of important inflammatory receptors in the retina such as TNFR1/2, TLR4, and CD14 were analyzed. We observed that TNFR1, TLR4, and CD14 were decreased in all tested periods (15 min, 45 min, 24 h, and 48 h). On the other hand, TNFR2 was increased after 24 h, suggesting an anti-inflammatory potential for ouabain. Moreover, we showed that ouabain also decreased Iba-1 (microglial marker) density. Subsequently, analyses of retrograde labeling of retinal ganglion cells (RGC) were performed after 48 h and showed that ouabain-induced RGC survival depends on autophagy. Using an autophagy inhibitor (3-methyladenine), we observed a complete blockage of the ouabain effect. Western blot analyses showed that ouabain increases the levels of autophagy proteins (LC3 and Beclin-1) coupled to p-CREB transcription factor and leads to autophagosome formation. Additionally, we found that the ratio of cleaved/pro-caspase-3 did not change after ouabain treatment; however, p-JNK density was enhanced. Also, ouabain decreased reactive oxygen species production immediately after axotomy. Taken together, our results suggest that ouabain controls neuroinflammation in the retina following optic nerve axotomy and promotes RGC neuroprotection through activation of the autophagy pathway.

IGF-1 and IGF-1R modulate the effects of IL-4 on retinal ganglion cells survival: The involvement of M1 muscarinic receptor

Trophic factors are involved in different cellular responses. Previously we demonstrated that IL-4 treatment induces an increase in retinal ganglion cell survival (RGCS) and regulates cholinergic differentiation of retinal cells in vitro. Data from literature show that IGF-1 also promotes RGCS, an effect mediated by PI-3K/AKT pathway. The aim of this study was to investigate the role of IGF-1 and IGF-1R on RGCS mediated by IL-4 treatment and the role of M1 acetylcholine receptors in this effect. Here we show that the effect of IL-4 on RGCS depends on IGF-1 and IGF-1R activation, the PI-3K/AKT and NFkB intracellular pathways and depends on M1 mAChRs activation. IGF-1 increases the levels of M1 mAChRs in 15min, 45min, 24 h and 48 h in mixed retinal cells culture, modulates the levels of IL-4, pIGF-1R, IGF-1R. IL-4 modulates IGF-1, pIGF-1R and IGF-1R levels in different time intervals. These results put in evidence a crosstalk between IL-4 and IGF-1 and a role of M1 mAChRs, IGF-1 and IGF-1R in RGCS mediated by IL-4.

Comprehensive analysis of vitreous chemokines involved in ischemic retinal vein occlusion

PURPOSE

To investigate vitreous levels of chemokines in eyes with ischemic retinal vein occlusion (RVO).

METHODS

The vitreous humor was collected at the start of 23-gauge pars plana vitrectomy from patients with ischemic RVO and patients with idiopathic preretinal membranes (PRMs) and idiopathic macular holes (IMHs). The levels of 40 different chemokines were measured using magnetic color-bead-based multiplex assay. The chi-square test was performed for clinical variables such as sex, and the Mann-Whitney U test was performed to evaluate the differences in the chemokine levels between the RVO group and the control group.

RESULTS

Vitreous humor was collected from 20 controls and 25 subjects with ischemic RVO. C-C motif ligand 17 (CCL17) was unmeasurable in more than 70% of the samples. The levels of 29 of 39 chemokines were statistically significantly elevated in the RVO group compared with the control group, including CCL21, C-X-C motif ligand (CXCL) 13, CCL27, CCL24, CX3CL1, CXCL6, interferon-gamma (IFN-γ), interleukin (IL) 1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-16, CXCL10, CXCL11, CCL8, CCL7, CCL13, CCL22, macrophage migration inhibitory factor (MIF), CXCL9, CCL3, CCL15, CCL20, CCL19, CCL23, CCL25, and tumor necrosis factor-alpha (TNF-α). Among the 29 elevated chemokines, we found that the levels of three chemokines (IL-8, CXCL9, and TNF-α) showed a more than six-fold increase in the RVO eyes versus controls, and CXCL9 expression showed the greatest change of all tested chemokines.

CONCLUSIONS

Dozens of chemokines were found to be elevated in the vitreous of RVO eyes complicated with vitreous hemorrhage, suggesting that inflammation is severe in the ischemic retina. The knowledge of specific upregulation of chemokines in ischemic RVO could allow more targeted future therapies.

Brain-derived neurotrophic factor: a mediator of inflammation-associated neurogenesis in Alzheimer's disease

In early- or late-onset Alzheimer's disease (AD), inflammation, which is triggered by pathologic conditions, influences the progression of neurodegeneration. Brain-derived neurotrophic factor (BDNF) has emerged as a crucial mediator of neurogenesis, because it exhibits a remarkable activity-dependent regulation of expression, which suggests that it may link inflammation to neurogenesis. Emerging evidence suggests that acute and chronic inflammation in AD differentially modulates neurotrophin functions, which are related to the roles of inflammation in neuroprotection and neurodegeneration. Recent studies also indicate novel mechanisms of BDNF-mediated neuroprotection, including the modulation of autophagy. Numerous research studies have demonstrated reverse parallel alterations between proinflammatory cytokines and BDNF during neurodegeneration; thus, we hypothesize that one mechanism that underlies the negative impact of chronic inflammation on neurogenesis is the reduction of BDNF production and function by proinflammatory cytokines.

IL-4 Induces Cholinergic Differentiation of Retinal Cells In Vitro

Interleukin-4 (IL-4) is a pleiotropic cytokine that regulates several phenomena, among them survival and differentiation of neuronal and glial cells. The aim of this work was to investigate the effect of IL-4 on the cholinergic differentiation of neonatal rat retinal cells in vitro, evaluating its effect on the levels of cholinergic markers (CHT1-high-affinity choline transporter; VAChT-vesicular acetylcholine transporter, ChAT-choline acetyltransferase, AChE-acetylcholinesterase), muscarinic receptors, and on the signaling pathways involved. Lister Hooded rat pups were used in postnatal days 0-2 (P0-P2). Our results show that IL-4 treatment (50 U/mL) for 48 h increases the levels of the cholinergic transporters VAChT and CHT1, the acetylcholinesterase activity, and the number of ChAT-positive cells. It also induces changes in muscarinic receptor levels, leading to a small decrease in M1 levels and a significant increase in M3 and M5 levels after 48 h of treatment. We also showed that IL-4 effect on M3 receptors is dependent on type I IL-4 receptor and on an increase in NFκB phosphorylation. These results indicate that IL-4 stimulates cholinergic differentiation of retinal cells.

Brain-derived neurotrophic factor enhances cholinergic contraction of longitudinal muscle of rabbit intestine via activation of phospholipase C

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family of proteins best known for its role in neuronal survival, differentiation, migration, and synaptic plasticity in central and peripheral neurons. BDNF is also widely expressed in nonneuronal tissues including the gastrointestinal tract. The role of BDNF in intestinal smooth muscle contractility is not well defined. The aim of this study was to identify the role of BDNF in carbachol (CCh)- and substance P (SP)-induced contraction of intestinal longitudinal smooth muscle. BDNF, selective tropomyosin-related kinase B (TrkB) receptor agonists, and pharmacological inhibitors of signaling pathways were examined for their effects on contraction of rabbit intestinal longitudinal muscle strips induced by CCh and SP. BDNF activation of intracellular signaling pathways was examined by Western blot in homogenates of muscle strips and isolated muscle cells. One-hour preincubation with BDNF enhanced intestinal muscle contraction induced by CCh but not by SP. The selective synthetic TrkB agonists LM 22A4 and 7,8-dihydroxyflavone produced similar effects to BDNF. The Trk antagonist K-252a, a TrkB antibody but not p75NTR antibody, blocked the effect of BDNF. The enhancement of CCh-induced contraction by BDNF was blocked by the phospholipase C (PLC) antagonist U73122, but not by ERK1/2 or Akt antagonists. Direct measurement in muscle strips and isolated muscle cells showed that BDNF caused phosphorylation of TrkB receptors and PLC-γ, but not ERK1/2 or Akt. We conclude that exogenous BDNF augments the CCh-induced contraction of longitudinal muscle from rabbit intestine by activating TrkB receptors and subsequent PLC activation.