Utility of LysM-cre and Cdh5-cre Driver Mice in Retinal and Brain Research: An Imaging Study Using tdTomato Reporter Mouse

Deletion of myeloid HDAC3 promotes efferocytosis to ameliorate retinal ischemic injury

Ischemia-induced retinopathy is a hallmark finding of common visual disorders including diabetic retinopathy (DR) and central retinal artery and vein occlusions. Treatments for ischemic retinopathies fail to improve clinical outcomes and the design of new therapies will depend on understanding the underlying disease mechanisms. Histone deacetylases (HDACs) are an enzyme class that removes acetyl groups from histone and non-histone proteins, thereby regulating gene expression and protein function. HDACs have been implicated in retinal neurovascular injury in preclinical studies in which nonspecific HDAC inhibitors mitigated retinal injury. Histone deacetylase 3 (HDAC3) is a class I histone deacetylase isoform that plays a central role in the macrophage inflammatory response. We recently reported that myeloid cells upregulate HDAC3 in a mouse model of retinal ischemia-reperfusion (IR) injury. However, whether this cellular event is an essential contributor to retinal IR injury is unknown. In this study, we explored the role of myeloid HDAC3 in ischemia-induced retinal neurovascular injury by subjecting myeloid-specific HDAC3 knockout (M-HDAC3 KO) and floxed control mice to retinal IR. The M-HDAC3 KO mice were protected from retinal IR injury as shown by the preservation of inner retinal neurons, vascular integrity, and retinal thickness. Electroretinography confirmed that this neurovascular protection translated to improved retinal function. The retinas of M-HDAC3 KO mice also showed less proliferation and infiltration of myeloid cells after injury. Interestingly, myeloid cells lacking HDAC3 more avidly engulfed apoptotic cells in vitro and after retinal IR injury in vivo compared to wild-type myeloid cells, suggesting that HDAC3 hinders the reparative phagocytosis of dead cells, a process known as efferocytosis. Further mechanistic studies indicated that although HDAC3 KO macrophages upregulate the reparative enzyme arginase 1 (A1) that enhances efferocytosis, the inhibitory effect of HDAC3 on efferocytosis is not solely dependent on A1. Finally, treatment of wild-type mice with the HDAC3 inhibitor RGFP966 ameliorated the retinal neurodegeneration and thinning caused by IR injury. Collectively, our data show that HDAC3 deletion enhances macrophage-mediated efferocytosis and protects against retinal IR injury, suggesting that inhibiting myeloid HDAC3 holds promise as a novel therapeutic strategy for preserving retinal integrity after ischemic insult.

miR-153 promotes neural differentiation by activating the cell adhesion/Ca2+ signaling pathway and targeting ion channel activity in HT-22 cells by bioinformatic analysis

MicroRNAs have been studied extensively in neurodegenerative diseases. In a previous study, miR-153 promoted neural differentiation and projection formation in mouse hippocampal HT-22 cells. However, the pathways and molecular mechanism underlying miR-153-induced neural differentiation remain unclear. To explore the molecular mechanism of miR-153 on neural differentiation, we performed RNA sequencing on miR-153-overexpressed HT-22 cells. Based on RNA sequencing, differentially expressed genes (DEGs) and pathways in miR-153-overexpressed cells were identified. The Database for Annotation, Visualization and Integrated Discovery and Gene Set Enrichment Analysis were used to perform functional annotation and enrichment analysis of DEGs. Targetscan predicted the targets of miR-153. The Search Tool for the Retrieval of Interacting Genes and Cytoscape, were used to construct protein-protein interaction networks and identify hub genes. Q-PCR was used to detect mRNA expression of the identified genes. The expression profiles of the identified genes were compared between embryonic days 9.5 (E9.5) and E11.5 in the embryotic mouse brain of the GDS3442 dataset. Cell Counting Kit-8 assay was used to determine cell proliferation and cellular susceptibility to amyloid β-protein (Aβ) toxicity in miR-153-overexpressed cells. The results indicated that miR-153 increased cell adhesion/Ca2+ (Cdh5, Nrcam, and P2rx4) and Bdnf/Ntrk2 neurotrophic signaling pathway, and decreased ion channel activity (Kcnc3, Kcna4, Clcn5, and Scn5a). The changes in the expression of the identified genes in miR-153-overexpressed cells were consistent with the expression profile of GDS3442 during neural differentiation. In addition, miR-153 overexpression decreased cellular susceptibility to Aβ toxicity in HT-22 cells. In conclusion, miR-153 overexpression may promote neural differentiation by inducing cell adhesion and the Bdnf/Ntrk2 pathway, and regulating electrophysiological maturity by targeting ion channels. MiR-153 may play an important role in neural differentiation; the findings provide a useful therapeutic direction for neurodegenerative diseases.

SOCS3 regulates pathological retinal angiogenesis through modulating SPP1 expression in microglia and macrophages

Pathological ocular angiogenesis has long been associated with myeloid cell activation. However, the precise cellular and molecular mechanisms governing the intricate crosstalk between the immune system and vascular changes during ocular neovascularization formation remain elusive. In this study, we demonstrated that the absence of the suppressor of cytokine signaling 3 (SOCS3) in myeloid cells led to a substantial accumulation of microglia and macrophage subsets during the neovascularization process. Our single-cell RNA sequencing data analysis revealed a remarkable increase in the expression of the secreted phosphoprotein 1 (Spp1) gene within these microglia and macrophages, identifying subsets of Spp1-expressing microglia and macrophages during neovascularization formation in angiogenesis mouse models. Notably, the number of Spp1-expressing microglia and macrophages exhibited further elevation during neovascularization in mice lacking myeloid SOCS3. Moreover, our investigation unveiled the Spp1 gene as a direct transcriptional target gene of signal transducer and activator of transcription 3. Importantly, pharmaceutical activation of SOCS3 or blocking of SPP1 resulted in a significant reduction in pathological neovascularization. In conclusion, our study highlights the pivotal role of the SOCS3/STAT3/SPP1 axis in the regulation of pathological retinal angiogenesis.

Role of myeloid cells in ischemic retinopathies: recent advances and unanswered questions

Myeloid cells including microglia and macrophages play crucial roles in retinal homeostasis by clearing cellular debris and regulating inflammation. These cells are activated in several blinding ischemic retinal diseases including diabetic retinopathy, where they may exert both beneficial and detrimental effects on neurovascular function and angiogenesis. Myeloid cells impact the progression of retinal pathologies and recent studies suggest that targeting myeloid cells is a promising therapeutic strategy to mitigate diabetic retinopathy and other ischemic retinal diseases. This review summarizes the recent advances in our understanding of the role of microglia and macrophages in retinal diseases and focuses on the effects of myeloid cells on neurovascular injury and angiogenesis in ischemic retinopathies. We highlight gaps in knowledge and advocate for a more detailed understanding of the role of myeloid cells in retinal ischemic injury to fully unlock the potential of targeting myeloid cells as a therapeutic strategy for retinal ischemia.

Myeloid cell-associated aromatic amino acid metabolism facilitates CNS myelin regeneration

Regulation of myeloid cell activity is critical for successful myelin regeneration (remyelination) in demyelinating diseases, such as multiple sclerosis (MS). Here, we show aromatic alpha-keto acids (AKAs) generated from the amino acid oxidase, interleukin-4 induced 1 (IL4I1), promote efficient remyelination in mouse models of MS. During remyelination, myeloid cells upregulated the expression of IL4I1. Conditionally knocking out IL4I1 in myeloid cells impaired remyelination efficiency. Mice lacking IL4I1 expression exhibited a reduction in the AKAs, phenylpyruvate, indole-3-pyruvate, and 4-hydroxyphenylpyruvate, in remyelinating lesions. Decreased AKA levels were also observed in people with MS, particularly in the progressive phase when remyelination is impaired. Oral administration of AKAs modulated myeloid cell-associated inflammation, promoted oligodendrocyte maturation, and enhanced remyelination in mice with focal demyelinated lesions. Transcriptomic analysis revealed AKA treatment induced a shift in metabolic pathways in myeloid cells and upregulated aryl hydrocarbon receptor activity in lesions. Our results suggest myeloid cell-associated aromatic amino acid metabolism via IL4I1 produces AKAs in demyelinated lesions to enable efficient remyelination. Increasing AKA levels or targeting related pathways may serve as a strategy to facilitate the regeneration of myelin in inflammatory demyelinating conditions.

Calbindin 2-specific deletion of arginase 2 preserves visual function after optic nerve crush

We previously found that global deletion of the mitochondrial enzyme arginase 2 (A2) limits optic nerve crush (ONC)-induced neuronal death. Herein, we examined the cell-specific role of A2 in this pathology by studies using wild type (WT), neuronal-specific calbindin 2 A2 KO (Calb2cre/+ A2 f/f), myeloid-specific A2 KO (LysMcre/+ A2f/f), endothelial-specific A2 KO (Cdh5cre/+ A2f/f), and floxed controls. We also examined the impact of A2 overexpression on mitochondrial function in retinal neuronal R28 cells. Immunolabeling showed increased A2 expression in ganglion cell layer (GCL) neurons of WT mice within 6 h-post injury and inner retinal neurons after 7 days. Calb2 A2 KO mice showed improved neuronal survival, decreased TUNEL-positive neurons, and improved retinal function compared to floxed littermates. Neuronal loss was unchanged by A2 deletion in myeloid or endothelial cells. We also found increased expression of neurotrophins (BDNF, FGF2) and improved survival signaling (pAKT, pERK1/2) in Calb2 A2 KO retinas within 24-hour post-ONC along with suppression of inflammatory mediators (IL1β, TNFα, IL6, and iNOS) and apoptotic markers (cleavage of caspase3 and PARP). ONC increased GFAP and Iba1 immunostaining in floxed controls, and Calb2 A2 KO dampened this effect. Overexpression of A2 in R28 cells increased Drp1 expression, and decreased mitochondrial respiration, whereas ABH-induced inhibition of A2 decreased Drp1 expression and improved mitochondrial respiration. Finally, A2 overexpression or excitotoxic treatment with glutamate significantly impaired mitochondrial function in R28 cells as shown by significant reductions in basal respiration, maximal respiration, and ATP production. Further, glutamate treatment of A2 overexpressing cells did not induce further deterioration in their mitochondrial function, indicating that A2 overexpression or glutamate insult induce comparable alterations in mitochondrial function. Our data indicate that neuronal A2 expression is neurotoxic after injury, and A2 deletion in Calb2 expressing neurons limits ONC-induced retinal neurodegeneration and improves visual function.

Myeloid cell deficiency of the inflammatory transcription factor Stat4 protects long-term synaptic plasticity from the effects of a high-fat, high-cholesterol diet

Neuroinflammation is associated with neurodegenerative diseases, including Alzheimer's and Parkinson's. The cytokine interleukin-12 activates signal transducer and activator of transcription 4 (Stat4), and consumption of a high-fat, high-cholesterol diet (HFD-C) and Stat4 activity are associated with inflammation, atherosclerosis, and a diabetic metabolic phenotype. In studies of in vitro hippocampal slices from control Stat4fl/flLdlr-/- mice fed a HFD-C diabetogenic diet, we show that Schaffer collateral-CA1 synapses exhibited larger reductions in activity-dependent, long-term potentiation (LTP) of synaptic transmission, compared to mice fed a standard diet. Glucose tolerance and insulin sensitivity shifts produced by HFD-C diet were reduced in Stat4ΔLysMLdlr-/- mice compared to Stat4fl/flLdlr-/- controls. Stat4ΔLysMLdlr-/- mice, which lack Stat4 under control of the LysMCre promoter, were resistant to HFD-C induced impairments in LTP. In contrast, Schaffer collateral-CA1 synapses in Stat4ΔLysMLdlr-/- mice fed the HFD-C diet showed larger LTP than control Stat4fl/flLdlr-/- mice. Expression of a number of neuroinflammatory and synaptic plasticity genes was reduced by HFD-C diet in control mice, and less affected by HFD-C diet in Stat4ΔLysMLdlr-/- mice. These data suggest that suppression of Stat4 activation may protect against effects of Western diet on cognition, type 2 diabetes, and reduce risk of Alzheimer's disease and other neurodegenerative disorders associated with neuroinflammation.

Pathological hemodynamic changes and leukocyte transmigration disrupt the blood-spinal cord barrier after spinal cord injury

BACKGROUND

Blood-spinal cord barrier (BSCB) disruption is a key event after spinal cord injury (SCI), which permits unfavorable blood-derived substances to enter the neural tissue and exacerbates secondary injury. However, limited mechanical impact is usually followed by a large-scale BSCB disruption in SCI. How the BSCB disruption is propagated along the spinal cord in the acute period of SCI remains unclear. Thus, strategies for appropriate clinical treatment are lacking.

METHODS

A SCI contusion mouse model was established in wild-type and LysM-YFP transgenic mice. In vivo two-photon imaging and complementary studies, including immunostaining, capillary western blotting, and whole-tissue clearing, were performed to monitor BSCB disruption and verify relevant injury mechanisms. Clinically applied target temperature management (TTM) to reduce the core body temperature was tested for the efficacy of attenuating BSCB disruption.

RESULTS

Barrier leakage was detected in the contusion epicenter within several minutes and then gradually spread to more distant regions. Membrane expression of the main tight junction proteins remained unaltered at four hours post-injury. Many junctional gaps emerged in paracellular tight junctions at the small vessels from multiple spinal cord segments at 15 min post-injury. A previously unnoticed pathological hemodynamic change was observed in the venous system, which likely facilitated gap formation and barrier leakage by exerting abnormal physical force on the BSCB. Leukocytes were quickly initiated to transverse through the BSCB within 30 min post-SCI, actively facilitating gap formation and barrier leakage. Inducing leukocyte transmigration generated gap formation and barrier leakage. Furthermore, pharmacological alleviation of pathological hemodynamic changes or leukocyte transmigration reduced gap formation and barrier leakage. TTM had very little protective effects on the BSCB in the early period of SCI other than partially alleviating leukocyte infiltration.

CONCLUSIONS

Our data show that BSCB disruption in the early period of SCI is a secondary change, which is indicated by widespread gap formation in tight junctions. Pathological hemodynamic changes and leukocyte transmigration contribute to gap formation, which could advance our understanding of BSCB disruption and provide new clues for potential treatment strategies. Ultimately, TTM is inadequate to protect the BSCB in early SCI.

LysM-positive neurons drive Tuberous Sclerosis Complex (TSC)-associated brain lesions

Mutations of Tsc1 or Tsc2 can lead to excessive activation of mTORC1 and cause Tuberous Sclerosis Complex (TSC), which is an autosomal dominant genetic disease prominently characterized by seizures, mental retardation and multiorgan hamartoma. In TSC, pathological changes in the central nervous system are the leading cause of death and disability. In decades, series of rodent models have been established by mutating Tsc1 or Tsc2 genes in diverse neural cell lineages to investigate the underlying cellular and molecular mechanisms, however, the cellular origin triggering neural pathological changes in TSC is undetermined. In this study, we generated a novel mouse model involving conditional deletion of Tsc1 in lysozyme 2 (Lyz2)-positive cells which replicated several features of brain lesions including epileptic seizures, megalencephaly, highly enlarged pS6-positive neurons and astrogliosis. In addition, we confirmed that bone marrow-derived myeloid cells including microglia with Tsc1 deficiency are not the decisive lineage in the cerebral pathologies in TSC. These histological assays in our murine model indicate an essential contribution of Lyz2-positive neurons to TSC progression. The Lyz2-positive neural population-specific onset of Tsc1 loss in murine postnatal brain might be the key to pathological phenotypes. Our findings thus provided evidences supporting new insights into the role of Lyz2-positive neurons in TSC events.

Preclinical investigation of Pegylated arginase 1 as a treatment for retina and brain injury

Arginase 1 (A1) is the enzyme that hydrolyzes the amino acid, L-arginine, to ornithine and urea. We have previously shown that A1 deletion worsens retinal ischemic injury, suggesting a protective role of A1. In this translational study, we aimed to study the utility of systemic pegylated A1 (PEG-A1, recombinant human arginase linked to polyethylene glycol) treatment in mouse models of acute retinal and brain injury. Cohorts of WT mice were subjected to retinal ischemia-reperfusion (IR) injury, traumatic optic neuropathy (TON) or brain cerebral ischemia via middle cerebral artery occlusion (MCAO) and treated with intraperitoneal injections of PEG-A1 or vehicle (PEG only). Drug penetration into retina and brain tissues was measured by western blotting and immunolabeling for PEG. Neuroprotection was measured in a blinded fashion by quantitation of NeuN (neuronal marker) immunolabeling of retina flat-mounts and brain infarct area using triphenyl tetrazolium chloride (TTC) staining. Furthermore, ex vivo retina explants and in vitro retina neuron cultures were subjected to oxygen-glucose deprivation (OGD) followed by reoxygenation (R) and treated with PEG-A1. PEG-A1 given systemically did not cross the intact blood-retina/brain barriers in sham controls but reached the retina and brain after injury. PEG-A1 provided neuroprotection after retinal IR injury, TON and cerebral ischemia. PEG-A1 treatment was also neuroprotective in retina explants subjected to OGD/R but did not improve survival in retinal neuronal cultures exposed to OGD/R. In summary, systemic PEG-A1 administration is neuroprotective and provides an excellent route to deliver the drug to the retina and the brain after acute injury.

Essential role of M1 macrophages in blocking cytokine storm and pathology associated with murine HSV-1 infection

Ocular HSV-1 infection is a major cause of eye disease and innate and adaptive immunity both play a role in protection and pathology associated with ocular infection. Previously we have shown that M1-type macrophages are the major and earliest infiltrates into the cornea of infected mice. We also showed that HSV-1 infectivity in the presence and absence of M2-macrophages was similar to wild-type (WT) control mice. However, it is not clear whether the absence of M1 macrophages plays a role in protection and disease in HSV-1 infected mice. To explore the role of M1 macrophages in HSV-1 infection, we used mice lacking M1 activation (M1^-/- mice). Our results showed that macrophages from M1^-/- mice were more susceptible to HSV-1 infection in vitro than were macrophages from WT mice. M1^-/- mice were highly susceptible to ocular infection with virulent HSV-1 strain McKrae, while WT mice were refractory to infection. In addition, M1^-/- mice had higher virus titers in the eyes than did WT mice. Adoptive transfer of M1 macrophages from WT mice to M1^-/- mice reduced death and rescued virus replication in the eyes of infected mice. Infection of M1^-/- mice with avirulent HSV-1 strain KOS also increased ocular virus replication and eye disease but did not affect latency-reactivation seen in WT control mice. Severity of virus replication and eye disease correlated with significantly higher inflammatory responses leading to a cytokine storm in the eyes of M1^-/- infected mice that was not seen in WT mice. Thus, for the first time, our study illustrates the importance of M1 macrophages specifically in primary HSV-1 infection, eye disease, and survival but not in latency-reactivation.

Macrophages circulating in the blood or present in different tissues constitute an important barrier against infection. We previously showed that the absence of M2 macrophages does not impact HSV-1 infectivity in vivo. However, in this study we demonstrated an essential role of M1 macrophages in protection from primary HSV-1 replication, death, and eye disease but not in latency-reactivation.

Retinal Pigment Epithelial Cells Express Antimicrobial Peptide Lysozyme - A Novel Mechanism of Innate Immune Defense of the Blood-Retina Barrier

Purpose

For this study we aimed to understand if retinal pigment epithelial (RPE) cells express antimicrobial peptide lysozyme as a mechanism to protect the neuroretina from blood-borne pathogens.

Methods

The expression of lysozyme in human and mouse RPE cells was examined by RT-PCR or immune (cyto)histochemistry in cell cultures or retinal sections. RPE cultures were treated with different concentrations of Pam3CSK4, lipopolysaccharides (LPS), staphylococcus aureus-derived peptidoglycan (PGN-SA), Poly(I:C), and Poly(dA:dT). The mRNA expression of lysozyme was examined by qPCR and protein expression by ELISA. Poly(I:C) was injected into the subretinal space of C57BL/6J mice and eyes were collected 24 hours later and processed for the evaluation of lysozyme expression by confocal microscopy. Bactericidal activity was measured in ARPE19 cells following LYZ gene deletion using Crispr/Cas9 technology.

Results

The mRNA and protein of lysozyme were detected in mouse and human RPE cells under normal conditions, although the expression levels were lower than mouse microglia BV2 or human monocytes THP-1 cells, respectively. Immunohistochemistry showed punctate lysozyme expression inside RPE cells. Lysozyme was detected by ELISA in normal RPE lysates, and in live bacteria-treated RPE supernatants. Treatment of RPE cells with Pam3CSK4, LPS, PGN-SA, and Poly(I:C) enhanced lysozyme expression. CRISPR/Cas9 deletion of lysozyme impaired bactericidal activity of ARPE19 cells and reduced their response to LPS and Poly(I:C) stimulation.

Conclusions

RPE cells constitutively express antimicrobial peptide lysozyme and the expression is modulated by pathogenic challenges. RPE cells may protect the neuroretina from blood-borne pathogens by producing antimicrobial peptides, such as lysozyme.

Myeloid Arginase 1 Insufficiency Exacerbates Amyloid-β Associated Neurodegenerative Pathways and Glial Signatures in a Mouse Model of Alzheimer's Disease: A Targeted Transcriptome Analysis

Brain myeloid cells, include infiltrating macrophages and resident microglia, play an essential role in responding to and inducing neurodegenerative diseases, such as Alzheimer's disease (AD). Genome-wide association studies (GWAS) implicate many AD casual and risk genes enriched in brain myeloid cells. Coordinated arginine metabolism through arginase 1 (Arg1) is critical for brain myeloid cells to perform biological functions, whereas dysregulated arginine metabolism disrupts them. Altered arginine metabolism is proposed as a new biomarker pathway for AD. We previously reported Arg1 deficiency in myeloid biased cells using lysozyme M (LysM) promoter-driven deletion worsened amyloidosis-related neuropathology and behavioral impairment. However, it remains unclear how Arg1 deficiency in these cells impacts the whole brain to promote amyloidosis. Herein, we aim to determine how Arg1 deficiency driven by LysM restriction during amyloidosis affects fundamental neurodegenerative pathways at the transcriptome level. By applying several bioinformatic tools and analyses, we found that amyloid-β (Aβ) stimulated transcriptomic signatures in autophagy-related pathways and myeloid cells' inflammatory response. At the same time, myeloid Arg1 deficiency during amyloidosis promoted gene signatures of lipid metabolism, myelination, and migration of myeloid cells. Focusing on Aβ associated glial transcriptomic signatures, we found myeloid Arg1 deficiency up-regulated glial gene transcripts that positively correlated with Aβ plaque burden. We also observed that Aβ preferentially activated disease-associated microglial signatures to increase phagocytic response, whereas myeloid Arg1 deficiency selectively promoted homeostatic microglial signature that is non-phagocytic. These transcriptomic findings suggest a critical role for proper Arg1 function during normal and pathological challenges associated with amyloidosis. Furthermore, understanding pathways that govern Arg1 metabolism may provide new therapeutic opportunities to rebalance immune function and improve microglia/macrophage fitness.

Deletion of Socs3 in LysM+ cells and Cx3cr1 resulted in age-dependent development of retinal microgliopathy

BACKGROUND

We generated a mouse model of primary microglial dysfunction by deleting two negative immune regulatory genes, Cx3cr1 and Socs3 (in LysM+ cells). This study aimed to understand how primary microglial dysfunction impacts retinal neurons during aging.

METHODS

The LysMCre-Socs3fl/flCx3cr1gfp/gfp double knockout (DKO), LysMCre-Socs3fl/fl, Cx3cr1gfp/gfp and Socs3fl/fl mice were maintained up to 12 months. Eyes were collected and processed for immunohistochemistry of IBA-1, cone arrestin, secretagogin, PKCα and GABA. Brain microglia from DKO and WT mice were stimulated with LPS + IFN-γ or IL-4. The expression of TNF-α, IL-1β, IL-6, iNOS, IL-12p40, IL-23p19, CCL2, CCL5, CXCL2, IL-10, CD206 and Arg1 were examined by qRT-PCR and protein production was measured by Luminex assay. Retinal explants from C57BL/6 J mice were co-cultured with microglia from DKO or WT mice for 24 h, after which the number of cone arrestin+ cells in retinal flatmount were quantified.

RESULTS

In 3-5 month old mice, the number of microglia in retinal ganglion cell layer (GCL) and inner plexiform layer (IPL) were comparable in all strains of mice. The DKO mice had a significantly higher number of microglia in the outer plexiform layer (OPL) but significantly lower numbers of cone arrestin+, secretagogin+ and GABA+ cells compared to Socs3fl/fl and single KO mice. During aging, 57% of the DKO mice died before 12 months old. The 10-12 months old DKO mice had significantly higher numbers of microglia in GCL/IPL and OPL than age-matched Socs3fl/fl and single KO mice. The aged DKO mice developed retinal pigment epithelial (RPE) dysmorphology accompanied by subretinal microglial accumulation. The number of photoreceptors, bipolar cells (Secretagogin+ or PKCα+) and GABA+ amacrine cells was significantly lower in aged DKO mice compared to age-matched Socs3fl/fl and single KO mice. Microglia from DKO mice showed significantly higher levels of phagocytic activity and produced higher levels of TNF-α, IL-6, CCL2, CCL5, CXCL2 and CXCL10 compared to microglia from Socs3fl/fl mice. Co-culture of retinal explants with LPS + IFN-γ or IL-4 pre-treated DKO microglia significantly reduced cone photoreceptor survival.

CONCLUSIONS

The LysMCre-Socs3fl/flCx3cr1gfp/gfp DKO mice displayed primary microglial dysfunction and developed age-related retinal microgliopathy characterized by aggragated microglial activation and multiple retinal neuronal and RPE degeneration.

TRIAL REGISTRATION

Not applicable. The article does not contain any results from human participants.

Arginase 1 Insufficiency Precipitates Amyloid-β Deposition and Hastens Behavioral Impairment in a Mouse Model of Amyloidosis

Alzheimer’s disease (AD) includes several hallmarks comprised of amyloid-β (Aβ) deposition, tau neuropathology, inflammation, and memory impairment. Brain metabolism becomes uncoupled due to aging and other AD risk factors, which ultimately lead to impaired protein clearance and aggregation. Increasing evidence indicates a role of arginine metabolism in AD, where arginases are key enzymes in neurons and glia capable of depleting arginine and producing ornithine and polyamines. However, currently, it remains unknown if the reduction of arginase 1 (Arg1) in myeloid cell impacts amyloidosis. Herein, we produced haploinsufficiency of Arg1 by the hemizygous deletion in myeloid cells using Arg1^fl/fl and LysMcre^Tg/+ mice crossed with APP Tg2576 mice. Our data indicated that Arg1 haploinsufficiency promoted Aβ deposition, exacerbated some behavioral impairment, and decreased components of Ragulator-Rag complex involved in mechanistic target of rapamycin complex 1 (mTORC1) signaling and autophagy. Additionally, Arg1 repression and arginine supplementation both impaired microglial phagocytosis in vitro. These data suggest that proper function of Arg1 and arginine metabolism in myeloid cells remains essential to restrict amyloidosis.