The Protective Role of Microglial PPARα in Diabetic Retinal Neurodegeneration and Neurovascular Dysfunction.

Microglial activation and subsequent pathological neuroinflammation contribute to diabetic retinopathy (DR). However, the underlying mechanisms of microgliosis, and means to effectively suppress pathological microgliosis, remain incompletely understood. Peroxisome proliferator-activated receptor alpha (PPARα) is a transcription factor that regulates lipid metabolism. The present study aimed to determine if PPARα affects pathological microgliosis in DR. In global Pparα mice, retinal microglia exhibited decreased structural complexity and enlarged cell bodies, suggesting microglial activation. Microglia-specific conditional Pparα-/- (PCKO) mice showed decreased retinal thickness as revealed by optical coherence tomography. Under streptozotocin (STZ)-induced diabetes, diabetic PCKO mice exhibited decreased electroretinography response, while diabetes-induced retinal dysfunction was alleviated in diabetic microglia-specific Pparα-transgenic (PCTG) mice. Additionally, diabetes-induced retinal pericyte loss was exacerbated in diabetic PCKO mice and alleviated in diabetic PCTG mice. In cultured microglial cells with the diabetic stressor 4-HNE, metabolic flux analysis demonstrated that Pparα ablation caused a metabolic shift from oxidative phosphorylation to glycolysis. Pparα deficiency also increased microglial STING and TNF-α expression. Taken together, these findings revealed a critical role for PPARα in pathological microgliosis, neurodegeneration, and vascular damage in DR, providing insight into the underlying molecular mechanisms of microgliosis in this context and suggesting microglial PPARα as a potential therapeutic target.

A Novel Role for Brain and Acute Leukemia Cytoplasmic (BAALC) in Human Breast Cancer Metastasis.

Brain and Acute Leukemia, Cytoplasmic (BAALC) is a protein that controls leukemia cell proliferation, differentiation, and survival and is overexpressed in several cancer types. The gene is located in the chromosomal region 8q22.3, an area commonly amplified in breast cancer and associated with poor prognosis. However, the expression and potential role of BAALC in breast cancer has not widely been examined. This study investigates BAALC expression in human breast cancers with the aim of determining if it plays a role in the pathogenesis of the disease. BAALC protein expression was examined by immunohistochemistry in breast cancer, and matched lymph node and normal breast tissue samples. The effect of gene expression on overall survival (OS), disease-free and distant metastasis free survival (DMFS) was assessed in silico using the Kaplan-Meier Plotter (n=3,935), the TCGA invasive breast carcinoma (n=960) and GOBO (n=821) data sets. Functional effects of BAALC expression on breast cancer proliferation, migration and invasion were determined in vitro. We demonstrate herein that BAALC expression is progressively increased in primary and breast cancer metastases when compared to normal breast tissue. Increased BAALC mRNA is associated with a reduction in DMFS and disease-free survival, but not OS, in breast cancer patients, even when corrected for tumor grade. We show that overexpression of BAALC in MCF-7 breast cancer cells increases the proliferation, anchorage-independent growth, invasion, and migration capacity of these cells. Conversely, siRNA knockdown of BAALC expression in Hs578T breast cancer cells decreases proliferation, invasion and migration. We identify that this BAALC associated migration and invasion is mediated by focal adhesion kinase (FAK)-dependent signaling and is accompanied by an increase in matrix metalloproteinase (MMP)-9 but not MMP-2 activity in vitro. Our data demonstrate a novel function for BAALC in the control of breast cancer metastasis, offering a potential target for the generation of anti-cancer drugs to prevent breast cancer metastasis.

Neuroprotective effects of PPARα in retinopathy of type 1 diabetes.

Diabetic retinopathy (DR) is a common neurovascular complication of type 1 diabetes. Current therapeutics target neovascularization characteristic of end-stage disease, but are associated with significant adverse effects. Targeting early events of DR such as neurodegeneration may lead to safer and more effective approaches to treatment. Two independent prospective clinical trials unexpectedly identified that the PPARα agonist fenofibrate had unprecedented therapeutic effects in DR, but gave little insight into the physiological and molecular mechanisms of action. The objective of the present study was to evaluate potential neuroprotective effects of PPARα in DR, and subsequently to identify the responsible mechanism of action. Here we reveal that activation of PPARα had a robust protective effect on retinal function as shown by Optokinetic tracking in a rat model of type 1 diabetes, and also decreased retinal cell death, as demonstrated by a DNA fragmentation ELISA. Further, PPARα ablation exacerbated diabetes-induced decline of visual function as demonstrated by ERG analysis. We further found that PPARα improved mitochondrial efficiency in DR, and decreased ROS production and cell death in cultured retinal neurons. Oxidative stress biomarkers were elevated in diabetic Pparα-/- mice, suggesting increased oxidative stress. Mitochondrially mediated apoptosis and oxidative stress secondary to mitochondrial dysfunction contribute to neurodegeneration in DR. Taken together, these findings identify a robust neuroprotective effect for PPARα in DR, which may be due to improved mitochondrial function and subsequent alleviation of energetic deficits, oxidative stress and mitochondrially mediated apoptosis.

Atypical Protein Kinase C: Breaking Down Barriers in Ocular Disease?

This commentary highlights the article by Lin et al that demonstrates the therapeutic potential of small-molecule atypical protein kinase C inhibitors in inflammatory ocular disease.

Microglia inhibit photoreceptor cell death and regulate immune cell infiltration in response to retinal detachment.

Retinal detachment (RD) is a sight-threatening complication common in many highly prevalent retinal disorders. RD rapidly leads to photoreceptor cell death beginning within 12 h following detachment. In patients with sustained RD, progressive visual decline due to photoreceptor cell death is common, leading to significant and permanent loss of vision. Microglia are the resident immune cells of the central nervous system, including the retina, and function in the homeostatic maintenance of the neuro-retinal microenvironment. It is known that microglia become activated and change their morphology in retinal diseases. However, the function of activated microglia in RD is incompletely understood, in part because of the lack of microglia-specific markers. Here, using the newly identified microglia marker P2ry12 and microglial depletion strategies, we demonstrate that retinal microglia are rapidly activated in response to RD and migrate into the injured area within 24 h post-RD, where they closely associate with infiltrating macrophages, a population distinct from microglia. Once in the injured photoreceptor layer, activated microglia can be observed to contain autofluorescence within their cell bodies, suggesting they function to phagocytose injured or dying photoreceptors. Depletion of retinal microglia results in increased disease severity and inhibition of macrophage infiltration, suggesting that microglia are involved in regulating neuroinflammation in the retina. Our work identifies that microglia mediate photoreceptor survival in RD and suggests that this effect may be due to microglial regulation of immune cells and photoreceptor phagocytosis.

The Role of DNA Repair Pathways in AML Chemosensitivity.

BACKGROUND: Defects in DNA repair pathways are causal factors for a plethora of solid tumours, but are only just beginning to be explored in haematological malignancies. Genomic instability, including mutations in DNA sequences, chromosomal aneuploidy, translocations and gene amplifications contribute to the development and progression of AML. Prior DNA damaging agent exposure enhances the risk of developing AML, as does inheritance of genetic syndromes that involve alterations in DNA repair pathways. Furthermore, these same variations are associated with sensitivity and resistance to a range of chemotherapeutics. Taken together, these studies suggest that defects within DNA repair pathways are involved in the pathogenesis and prognosis of AML. OBJECTIVE: This review summarises the major DNA repair pathways, and presents an overview of current data on DNA damage repair abnormalities in AML as they pertain to the development of resistance and sensitivity to chemotherapeutics in AML. Additionally, the use of drugs that modulate these pathways as new treatments for AML will be explored herein. CONCLUSION: This review highlights that abnormalities in DNA repair mechanisms in AML cells are potential novel treatment targets for AML patients with disease that is resistant to current therapies.

PPARα is essential for retinal lipid metabolism and neuronal survival.

BACKGROUND: Peroxisome proliferator activated receptor-alpha (PPARα) is a ubiquitously expressed nuclear receptor. The role of endogenous PPARα in retinal neuronal homeostasis is unknown. Retinal photoreceptors are the highest energy-consuming cells in the body, requiring abundant energy substrates. PPARα is a known regulator of lipid metabolism, and we hypothesized that it may regulate lipid use for oxidative phosphorylation in energetically demanding retinal neurons. RESULTS: We found that endogenous PPARα is essential for the maintenance and survival of retinal neurons, with Pparα -/- mice developing retinal degeneration first detected at 8 weeks of age. Using extracellular flux analysis, we identified that PPARα mediates retinal utilization of lipids as an energy substrate, and that ablation of PPARα ultimately results in retinal bioenergetic deficiency and neurodegeneration. This may be due to PPARα regulation of lipid transporters, which facilitate the internalization of fatty acids into cell membranes and mitochondria for oxidation and ATP production. CONCLUSION: We identify an endogenous role for PPARα in retinal neuronal survival and lipid metabolism, and furthermore underscore the importance of fatty acid oxidation in photoreceptor survival. We also suggest PPARα as a putative therapeutic target for age-related macular degeneration, which may be due in part to decreased mitochondrial efficiency and subsequent energetic deficits.

Palmitoylation and membrane cholesterol stabilize µ-opioid receptor homodimerization and G protein coupling.

BACKGROUND: A cholesterol-palmitoyl interaction has been reported to occur in the dimeric interface of the ß2-adrenergic receptor crystal structure. We sought to investigate whether a similar phenomenon could be observed with µ-opioid receptor (OPRM1), and if so, to assess the role of cholesterol in this class of G protein-coupled receptor (GPCR) signaling. RESULTS: C3.55(170) was determined to be the palmitoylation site of OPRM1. Mutation of this Cys to Ala did not affect the binding of agonists, but attenuated receptor signaling and decreased cholesterol associated with the receptor signaling complex. In addition, both attenuation of receptor palmitoylation (by mutation of C3.55[170] to Ala) and inhibition of cholesterol synthesis (by treating the cells with simvastatin, a HMG-CoA reductase inhibitor) impaired receptor signaling, possibly by decreasing receptor homodimerization and Gαi2 coupling; this was demonstrated by co-immunoprecipitation, immunofluorescence colocalization and fluorescence resonance energy transfer (FRET) analyses. A computational model of the OPRM1 homodimer structure indicated that a specific cholesterol-palmitoyl interaction can facilitate OPRM1 homodimerization at the TMH4-TMH4 interface. CONCLUSIONS: We demonstrate that C3.55(170) is the palmitoylation site of OPRM1 and identify a cholesterol-palmitoyl interaction in the OPRM1 complex. Our findings suggest that this interaction contributes to OPRM1 signaling by facilitating receptor homodimerization and G protein coupling. This conclusion is supported by computational modeling of the OPRM1 homodimer.