bFGF-mediated redox activation of the PI3K/Akt pathway in retinal photoreceptor cells

Bleomycin induces epithelial-to-mesenchymal transition via bFGF/PI3K/ESRP1 signaling in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal and chronic disease with a high rate of infection and mortality; however, its etiology and pathogenesis remain unclear. Studies have revealed that epithelial–mesenchymal transition (EMT) is a crucial cellular event in IPF. Here, we identified that the pulmonary fibrosis inducer bleomycin simultaneously increased the expression of bFGF and TGF-β1 and inhibited epithelial-specific regulatory protein (ESRP1) expression in vivo and in vitro. In addition, in vitro experiments showed that bFGF and TGF-β1 down-regulated the expression of ESRP1 and that silencing ESRP1 promoted EMT in A549 cells. Notably, we determined that bFGF activates PI3K/Akt signaling, and treatment with the PI3K/Akt inhibitor LY294002 inhibited bleomycin-induced cell morphology changes and EMT. In addition, the effects of LY294002 on bleomycin-induced EMT were inhibited by ESRP1 silencing in A549 cells. Taken together, these findings suggest that bleomycin induced EMT through down-regulating ESRP1 by simultaneously increasing bFGF and TGF-β1 in pulmonary fibrosis. Additionally, our findings indicated that bFGF inhibits ESRP1 by activating PI3K/Akt signaling.

NLRX1 Enhances Glutamate Uptake and Inhibits Glutamate Release by Astrocytes

Uptake of glutamate from the extracellular space and glutamate release to neurons are two major processes conducted by astrocytes in the central nervous system (CNS) that protect against glutamate excitotoxicity and strengthen neuronal firing, respectively. During inflammatory conditions in the CNS, astrocytes may lose one or both of these functions, resulting in accumulation of the extracellular glutamate, which eventually leads to excitotoxic neuronal death, which in turn worsens the CNS inflammation. NLRX1 is an innate immune NOD-like receptor that inhibits the major inflammatory pathways. It is localized in the mitochondria and was shown to inhibit cell death, enhance ATP production, and dampen oxidative stress. In the current work, using primary murine astrocyte cultures from WT and Nlrx1^-/- mice, we demonstrate that NLRX1 potentiates astrocytic glutamate uptake by enhancing mitochondrial functions and the functional activity of glutamate transporters. Also, we report that NLRX1 inhibits glutamate release from astrocytes by repressing Ca²⁺-mediated glutamate exocytosis. Our study, for the first time, identified NLRX1 as a potential regulator of glutamate homeostasis in the CNS.

Pro-survival redox signalling in progesterone-mediated retinal neuroprotection

Retinitis pigmentosa (RP) is a group of hereditary retinal diseases, characterised by photoreceptor cell loss. Despite a substantial understanding of the mechanisms leading to cell death, an effective therapeutic strategy is sought. Our laboratory has previously demonstrated the neuroprotective properties of Norgestrel, a progesterone analogue, in the degenerating retina, mediated in part by the neurotrophic factor basic fibroblast growth factor (bFGF). In other retinal studies, we have also presented a pro-survival role for reactive oxygen species (ROS), downstream of bFGF. Thus, we hypothesized that Norgestrel utilises bFGF-driven ROS production to promote photoreceptor survival. Using the 661W photoreceptor-like cell line, we now show that Norgestrel, working through progesterone receptor membrane complex 1 (PGRMC1); generates an early burst of pro-survival bFGF-induced ROS. Using the rd10 mouse model of RP, we confirm that Norgestrel induces a similar early pro-survival increase in retinal ROS. Norgestrel-driven protection in the rd10 retina was attenuated in the presence of antioxidants. This study therefore presents an essential role for ROS signalling in Norgestrel-mediated neuroprotection in vitro and demonstrates that Norgestrel employs a similar pro-survival mechanism in the degenerating retina.

Human Basic Fibroblast Growth Factor Inhibits Tau Phosphorylation via the PI3K/Akt-GSK3β Signaling Pathway in a 6-Hydroxydopamine-Induced Model of Parkinson's Disease

BACKGROUND

Basic fibroblast growth factor (bFGF) has been increasingly investigated due to its neuroprotection in neurodegenerative disorders. Because there are still no cures for any of these disorders, it is crucial to identify new therapeutic targets and screen potential drugs. The increased phosphorylation of tau at Ser396 leads to intracellular tau accumulation, which forms neurofibrillary tangles in Parkinson's disease (PD). In this study, neuroprotection by bFGF was observed, and the mechanisms related to its regulation of phosphorylated tau were investigated.

METHODS

bFGF-loaded liposome carriers were intranasally administered to rats. The neuroprotective effects of bFGF were assessed in a PD model induced by 6-hydroxydopamine (6-OHDA) in vivo and in vitro. The phosphorylation of tau was measured, and the PI3K/Akt-GSK3β signaling pathway was investigated.

RESULTS

Our study demonstrated that liposomes markedly assisted in the delivery of bFGF to the striatum and substantia nigra of rats and enhanced the neuroprotective effects of bFGF on dopaminergic neurons. bFGF treatment significantly ameliorated the behavioral deficits induced by 6-OHDA, rescued the loss of tyrosine hydroxylase-positive neurons and increased the number of Nissl bodies. bFGF reduced the phosphorylation of tau and GSK3β and increased the phosphorylation of PI3K/Akt.

CONCLUSION

Liposomes markedly assisted in the delivery of bFGF to the brain and enhanced the neuroprotective effects of bFGF by inhibiting the phosphorylation of tau. bFGF down-regulated the phosphorylation of tau by increasing the phosphorylation of GSK3β via the PI3K/Akt signaling pathway. These findings provide a new vision of bFGF as a potential therapy for PD.

The synthetic progesterone Norgestrel is neuroprotective in stressed photoreceptor-like cells and retinal explants, mediating its effects via basic fibroblast growth factor, protein kinase A and glycogen synthase kinase 3β signalling

The synthetic progesterone Norgestrel has been shown to have proven neuroprotective efficacy in two distinct models of retinitis pigmentosa: the rd10/rd10 (B6.CXBI-Pde6b(rd10)/J) mouse model and the Balb/c light-damage model. However, the cellular mechanism underlying this neuroprotection is still largely unknown. Therefore, this study aimed to examine the downstream signalling pathways associated with Norgestrel both in vitro and ex vivo. In this work, we identify the potential of Norgestrel to rescue stressed 661W photoreceptor-like cells and ex vivo retinal explants from cell death over 24 h. Norgestel is thought to work through an upregulation of neuroprotective basic fibroblast growth factor (bFGF). Analysis of 661W cells in vitro by real-time polymerase chain reaction (rt-PCR), enzyme-linked immunosorbent assay (ELISA) and Western blotting revealed an upregulation of bFGF in response to Norgestrel over 6 h. Specific siRNA knockdown of bFGF abrogated the protective properties of Norgestrel on damaged photoreceptors, thus highlighting the crucial importance of bFGF in Norgestrel-mediated protection. Furthermore, Norgestrel initiated a bFGF-dependent inactivation of glycogen synthase kinase 3β (GSK3β) through phosphorylation at serine 9. The effects of Norgestrel on GSK3β were dependent on protein kinase A (PKA) pathway activation. Specific inhibition of both the PKA and GSK3β pathways prevented Norgestrel-mediated neuroprotection of stressed photoreceptor cells in vitro. Involvement of the PKA pathway following Norgestrel treatment was also confirmed ex vivo. Therefore, these results indicate that the protective efficacy of Norgestrel is, at least in part, due to the bFGF-mediated activation of the PKA pathway, with subsequent inactivation of GSK3β.

Decellularized retinal matrix: Natural platforms for human retinal progenitor cell culture

Tissue decellularization strategies have enabled engineering of scaffolds that preserve native extracellular matrix (ECM) structure and composition. In this study, we developed decellularized retina (decell-retina) thin films. We hypothesized that these films, mimicking the retina niche, would promote human retinal progenitor cell (hRPC) attachment, proliferation and differentiation. Retinas isolated from bovine eyes were decellularized using 1% w/v sodium dodecyl sulfate (SDS) and pepsin digested. The resulting decell-retina was biochemically assayed for composition and cast dried to develop thin films. Attachment, viability, morphology, proliferation and gene expression of hRPC cultured on the films were studied in vitro. Biochemical analyses of decell-retina compared to native retina indicated the bulk of DNA (94%) was removed, while the majority of sulfated GAGs (55%), collagen (83%), hyaluronic acid (87%), and key growth factors were retained. The decell-retina films supported hRPC attachment and growth, with cell number increasing 1.5-fold over a week. RT-PCR analysis revealed hRPC expression of rhodopsin, rod outer membrane, neural retina-specific leucine zipper neural and cone-rod homeobox gene on decell-retina films, indicating photoreceptor development. In conclusion, novel decell-retina films show promise as potential substrates for culture and/or transplantation of retinal progenitor cells to treat retinal degenerative disorders.

STATEMENT OF SIGNIFICANCE

In this study, we report the development of a novel biomaterial, based on decellularized retina (decell-retina) that mimics the retina niche and promotes human retinal progenitor cell (hRPC) attachment, proliferation and differentiation. We estimated, for the first time, the amounts of collagen I, GAGs and HA present in native retina, as well as the decell-retina. We demonstrated that retinas can be decellularized using ionic detergents and can be processed into mechanically stable thin films, which can act as substrates for culturing hRPCs. Rhodopsin, ROM1, NRL and CRX gene expression on the decell-retina films indicated photoreceptor development from RPCs. These results support the potential of decell-retina as a cell delivery platform to treat and manage retinal degenerative disease like AMD.

Elevation of Microglial Basic Fibroblast Growth Factor Contributes to Development of Neuropathic Pain after Spinal Nerve Ligation in Rats

STUDY DESIGN

Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistological analysis of spinal cord and pain behavior analysis in a rat neuropathic pain model were conducted to examine the function of microglial basic fibroblast growth factor (bFGF) in the development of neuropathic pain.

OBJECTIVE

To investigate the role of bFGF in spinal microglia during the development of allodynia following spinal nerve ligation in rats.

SUMMARY OF BACKGROUND DATA

Evidence suggests that the production of bFGF by spinal cord glial cells is increased in response to peripheral nerve injury. Although an association between bFGF and astrocytes has been widely reported, the relationship between bFGF and microglia, particularly with respect to the development of neuropathic pain, remains poorly understood.

METHODS

Spinal nerve ligation rats were used. After surgery, bFGF expression in the spinal cord was investigated using RT-PCR and immunohistochemistry. Neutralizing antibodies to bFGF were injected intrathecally into rats after spinal nerve ligaton. Spinal cords were used for RT-PCR analysis and pain behavior was analyzed using the von Frey test.

RESULTS

bFGF mRNA expression was significantly increased in the spinal cord 6 hours after spinal nerve ligation compared with untreated rats. Immunohistochemical analysis revealed that bFGF co-localized with ionized calcium-binding adaptor molecule 1, a microglial marker, and myeloperoxidase. Neutralizing antibodies to bFGF attenuated mechanical allodynia and myeloperoxidase mRNA expression.

CONCLUSION

bFGF increased in spinal microglia during the development allodynia after spinal nerve ligation. Thus, controlling bFGF release from microglia during the acute stage of peripheral nerve injury may suppress the progression of allodynia.

LEVEL OF EVIDENCE

N/A.

Light, lipids and photoreceptor survival: live or let die?

Due to its constant exposure to light and its high oxygen consumption the retina is highly sensitive to oxidative damage, which is a common factor in inducing the death of photoreceptors after light damage or in inherited retinal degenerations. The high content of docosahexaenoic acid (DHA), the major polyunsaturated fatty acid in the retina, has been suggested to contribute to this sensitivity. DHA is crucial for developing and preserving normal visual function. However, further roles of DHA in the retina are still controversial. Current data support that it can tilt the scale either towards degeneration or survival of retinal cells. DHA peroxidation products can be deleterious to the retina and might lead to retinal degeneration. However, DHA has also been shown to act as, or to be the source of, a survival molecule that protects photoreceptors and retinal pigment epithelium cells from oxidative damage. We have established that DHA protects photoreceptors from oxidative stress-induced apoptosis and promotes their differentiation in vitro. DHA activates the retinoid X receptor (RXR) and the ERK/MAPK pathway, thus regulating the expression of anti and pro-apoptotic proteins. It also orchestrates a diversity of signaling pathways, modulating enzymatic pathways that control the sphingolipid metabolism and activate antioxidant defense mechanisms to promote photoreceptor survival and development. A deeper comprehension of DHA signaling pathways and context-dependent behavior is required to understand its dual functions in retinal physiology.

Assessment of oxidative metabolism

Oxidative metabolism is one of the central physiological processes that regulate multiple functions in a cell including cell death and survival, proliferation, gene transcription, and protein modification. There are multitudes of techniques that are used to evaluate oxidative activity. Here, we summarize how to measure oxidative activity by flow cytometry. This versatile technique allows the evaluation of the level of oxidative activity within heterogeneous populations of cells and in cell culture. Flow cytometry is a quick method that yields highly reproducible results with small sample volumes. Therefore, it is an ideal technique for evaluating changes in oxidative activity in samples from mice.

Preventing retinal apoptosis--is there a common therapeutic theme?

There is an urgent need for therapies for retinal diseases; retinitis pigmentosa sufferers have no treatment options available and those targeted at other retinopathies have shown limited effectiveness. The process of programmed cell death or apoptosis although complex, remains a possible target for the treatment of retinal diseases. Having identified apoptosis in the vertebrate retina in populations of immature neurons as an essential part of development it was proposed that re-activation of these developmental cell death pathways might provide insight into the death mechanisms operating in retinal diseases. However, the discovery that numerous factors initiate and mediate the apoptotic cascade in mature photoreceptors has resulted in a relatively untargeted approach to examining and arresting apoptosis in the retina. In the last 5 years, mouse models have been treated with a diverse range of drugs or factors including anti-oxidants, growth factors, steroid hormones, calcium/calpain inhibitors and tetracycline antibiotics. Therefore to draw a unifying theme from these broad research areas is challenging. However, this review focusses on two targets which are currently under investigation, reactive oxygen species and mammalian target of rapamycin, drawing together the common themes of these research areas.