Melatonin attenuates oxidative stress and inflammation of Müller cells in diabetic retinopathy via activating the Sirt1 pathway

Oxidative stress and inflammation are important pathogenic factors of diabetic retinopathy (DR). DR remains the most common ocular complication caused by diabetes mellitus (DM) and is the leading cause of visual impairment in working-aged people worldwide. Melatonin has attracted extensive attention due to its potent antioxidant and anti-inflammatory effects. In the present study, melatonin inhibited oxidative stress and inflammation by enhancing the expression and activity of silent information regulator factor 2-related enzyme 1 (Sirt1) both in in vitro and in vivo models of DR, and the Sirt1 inhibitor EX-527 counteracted melatonin-mediated antioxidant and anti-inflammatory effects on Müller cells. Moreover, melatonin enhanced Sirt1 activity through the maternally expressed gene 3 (MEG3)/miR-204 axis, leading to the deacetylation of the Sirt1 target genes forkhead box o1 (Foxo1) and nuclear factor kappa B (NF-κB) subunit p65, eventually contribute to the alleviation of oxidative stress and inflammation. The study revealed that melatonin promotes the Sirt1 pathway, thereby protecting the retina from DM-induced damage.

Role of Müller cell cytochrome P450 2c44 in murine retinal angiogenesis

Polyunsaturated fatty acids (PUFA) and their cytochrome P450 (CYP450) metabolites have been linked to angiogenesis and vessel homeostasis. However, the role of individual CYP isoforms and their endogenous metabolites in those processes are not clear. Here, we focused on the role of Cyp2c44 in postnatal retinal angiogenesis and report that Cyp2c44 is highly expressed in Müller glial cells in the retina. The constitutive as well as inducible postnatal genetic deletion of Cyp2c44 resulted in an increased vessel network density without affecting vessel radial expansion during the first postnatal week. This phenotype was associated with an increased endothelial cell proliferation and attenuated Notch signaling. LC-MS/MS analyses revealed that levels of hydroxydocosahexaenoic acids (HDHA), i.e., 10-, 17- and 20-HDHA were significantly elevated in retinas from 5day old Cyp2c44^-/- mice compared to their wild-type littermates. Enzymatic activity assays revealed that HDHAs were potential substrates for Cyp2c44 which could account for the increased levels of HDHAs in retinas from Cyp2c44^-/- mice. These data indicate that Cyp2c44 is expressed in the murine retina and, like the soluble epoxide hydrolase, is expressed in Müller glia cells. The enhanced endothelial cell proliferation and Notch inhibition seen in retinas from Cyp2c44-deficient mice indicate a role for Cyp2c44-derived lipid mediators in physiological angiogenesis.

Retinol Dehydrogenases Regulate Vitamin A Metabolism for Visual Function

The visual system produces visual chromophore, 11-cis-retinal from dietary vitamin A, all-trans-retinol making this vitamin essential for retinal health and function. These metabolic events are mediated by a sequential biochemical process called the visual cycle. Retinol dehydrogenases (RDHs) are responsible for two reactions in the visual cycle performed in retinal pigmented epithelial (RPE) cells, photoreceptor cells and Müller cells in the retina. RDHs in the RPE function as 11-cis-RDHs, which oxidize 11-cis-retinol to 11-cis-retinal in vivo. RDHs in rod photoreceptor cells in the retina work as all-trans-RDHs, which reduce all-trans-retinal to all-trans-retinol. Dysfunction of RDHs can cause inherited retinal diseases in humans. To facilitate further understanding of human diseases, mouse models of RDHs-related diseases have been carefully examined and have revealed the physiological contribution of specific RDHs to visual cycle function and overall retinal health. Herein we describe the function of RDHs in the RPE and the retina, particularly in rod photoreceptor cells, their regulatory properties for retinoid homeostasis and future therapeutic strategy for treatment of retinal diseases.

Apoptotic effect of mtrix metalloproteinases 9 in the development of diabetic retinopathy

OBJECTIVE

To explore the potential regulatory mechanism of MMP9 in the development of DR.

METHODS

Plasmids pcDNA-MMP9 and pcDNA-Ang2 were transfected into primary rat retinal Müller cells (RMCs) using Lipofectamine 2000. Cell viability and apoptosis were respectively determined by MTT assay and flow cytometry. Moreover, the interaction between MMP9 and Ang2 was explored. Besides, RMCs were treated with MMP-9 under normal glucose and high glucose condition for 2d. Besides, the expression levels of apoptotic proteins, like MMP9, Ang2, Bax2, Bcl2, cleaved PARP and cleaved caspase3 were determined by Western blot.

RESULTS

The cell viability of siRNA-MMP9 group was significantly increased while decreased in MMP9 overexpression group when compared to control group, respectively. The apoptotic cells in MMP9 overexpression group significantly increased while decreased in siRNA-MMP9 group when compared with control group. MMP9 expression was significantly regulated by Ang2 whereas no significant changes occurred in Ang2 expression when MMP9 expression changed. Moreover, MMP9 expression in HG group significantly increased while there were no significant differences between NG group and control group. Besides, the expression of Bax2, Bcl2, cleaved PARP and cleaved caspase3 in HG group increased while there were no significant differences between NG group and control group.

CONCLUSION

Our findings indicate that MMP9 may play an important role via inducing cell apoptosis in the development of DR via regulating by Ang2 or targeting apoptotic proteins, such as Bax2, Bcl2, cleaved PARP and cleaved caspase3.

Fasting Enhances Pyroglutamyl Peptidase II Activity in Tanycytes of the Mediobasal Hypothalamus of Male Adult Rats

Fasting down-regulates the hypothalamus-pituitary-thyroid (HPT) axis activity through a reduction of TRH synthesis in neurons of the parvocellular paraventricular nucleus of the hypothalamus (PVN). These TRH neurons project to the median eminence (ME), where TRH terminals are close to the cytoplasmic extensions of β2 tanycytes. Tanycytes express pyroglutamyl peptidase II (PPII), the TRH-degrading ectoenzyme that controls the amount of TRH that reaches the anterior pituitary. We tested the hypothesis that regulation of ME PPII activity is another mechanism by which fasting affects the activity of the HPT axis. Semiquantitative in situ hybridization histochemistry data indicated that PPII and deiodinase 2 mRNA levels increased in tanycytes after 48 hours of fasting. This increase was transitory, followed by an increase of PPII activity in the ME, and a partial reversion of the reduction in PVN pro-TRH mRNA levels and the number of TRH neurons detected by immunohistochemistry. In fed animals, adrenalectomy and corticosterone treatment did not change ME PPII activity 72 hours later. Methimazole-induced hypothyroidism produced a profound drop in tanycytes PPII mRNA levels, which was reverted by 3 days of treatment with T4. The activity of thyroliberinase, the serum isoform of PPII, was increased at most fasting time points studied. We conclude that delayed increases in both the ME PPII as well as the thyroliberinase activities in fasted male rats may facilitate the maintenance of the deep down-regulation of the HPT axis function, despite a partial reactivation of TRH expression in the PVN.

Radial glial cell: critical functions and new perspective as a steroid synthetic cell

The radial glial cell (RGC) is a glial cell type in the central nervous system of all vertebrates. Adult teleost fish have abundant RGCs in the brain in contrast to mammals. Adult fish RGCs have many important functions, including forming a structural scaffold to guide neuronal migration and serving as the progenitor cells in the brain to generate neurons. The role of the RGC in adult neurogenesis explains the high regenerative capacity of adult fish brain. There is increasing evidence from several species that some glial cells produce or metabolize steroids. It is now well-known that teleost RGCs express aromatase and produce estrogens from androgen precursors, which may be important for local neuroendocrine functions and regulation of neurogenesis. The question of whether RGCs are capable of de novo steroid synthesis from cholesterol remains unanswered. However, the expression of steroidogenic acute regulatory protein, and the key enzyme cytochrome P450 17alpha-hydroxylase in primary cultures of goldfish RGCs indicate the potential to produce 17α-hydroxy-pregnenolone and thus other steroid intermediates. The possibility of synthesizing additional non-estrogenic steroids may indicate new functions for the RGC.

ERK1/2 pathway is activated in degenerated Rpe65-deficient mice

The MAPK family is composed of three majors kinases, JNK, p38 and ERK1/2, and is implicated in many degenerative processes, including retinal cell death. The purpose of our study was to evaluate the activation of ERK1/2 kinase, and its potential role in Müller cell gliosis, during photoreceptor cell death in Rpe65(-/-) mice. We assayed ERK1/2 mRNA and protein levels, and evaluated ERK1/2 phosphorylation involved in kinase activation, in 2, 4 and 6 month-old Rpe65(-/-) mice and in age-matched wild-type controls. No differences in ERK1/2 expression were detected between Rpe65(-/-) and wild-type mice, however, ERK1/2 phosphorylation was dramatically increased in the knock out mice at 4 and 6 months-of-age. Phosphorylated ERK1/2 co-localized with GFAP in the ganglion cell layer, and correlated with an increase in GFAP protein expression and retinal cell death. Accumulation of cFOS protein in the ganglion cell layer occurred concomitant with pERK1/2 activation. Müller cell proliferation was not observed. ERK1/2 activation did not occur in 2 month-old Rpe65(-/-) or in the Rpe65(-/-)/Gnat1(-/-) mice, in which no degeneration was evident. The observed activation ERK1/2 and GFAP, both markers of Müller cell gliosis, in the absence of Müller cell proliferation, is consistent with the activation of atypical gliosis occurring during the slow process of degeneration in Rpe65(-/-) mice. As Müller cell gliosis is activated in many neuronal and retinal degenerative diseases, further studies will be needed to determine whether atypical gliosis in Rpe65(-/-) mice contributes to, or protects against, the pathogenesis occurring in this model of Leber congenital amaurosis.