Biology subjects

McNeel, R.

Publications and source records attributed to McNeel, R..

6 recordsLinked to original sources

bioRxiv2026

Aging Differentially Remodels the Retina and RPE/Choroid Proteome and Metabolism

Purpose: The neural retina and retinal pigment epithelium/choroid (RPE/Cho) are metabolically coupled. Metabolic dysfunction of the RPE/Cho contributes to photoreceptor death in age-related macular degeneration (AMD). This study aimed to determine how aging, a major risk factor for AMD, alters the proteome and metabolic pathways in the retina and RPE/Cho. Methods: We performed quantitative proteomics on neural retina and RPE/Cho from young (8-week) and old (73-week) C57BL/6J mice. The differentially expressed proteins between old and young, as well as between the retina and RPE/Cho, were visualized using volcano plots and heatmaps, and functional analyses were assessed by Gene Ontology enrichment tools. Results: Aging altered the expression of 85 retinal proteins and 272 RPE/Cho, with 16 shared between tissues. In the aged retina, proteins associated with NADP(H) metabolism, neurodegeneration, and immunity were mostly upregulated, while proteins in lipid metabolism, transcription, and epigenetic regulation decreased. In the aged RPE/Cho, all 21 significantly altered lysosomal enzymes and transport proteins increased, together with complement components, and photoreceptor outer segment proteins. These changes accompanied increases in proteins associated with lipid metabolism and protection against lipid peroxidation, while several glutathione metabolism enzymes decreased. Seven shared proteins involved in lipid and NADP(H) metabolism, changed in opposite directions between retina and RPE/Cho. Comparison of the retinal and RPE/Cho proteomes identified 3073 differentially abundant proteins, of which 2452 maintained tissue-specific differences across both age groups, while approximately 17% showed age-dependent shifts in tissue enrichment. These shifts involved proteins associated with metabolism, extracellular matrix, visual function, lysosomal pathways, and innate immunity. Within the metabolic proteome, several glycolytic and fatty acid oxidation proteins showed greater relative enrichment in RPE/Cho with age, whereas glucose transporters and mitochondrial complexes shifted toward the retina. Conclusions: Overall, these findings show that aging differentially remodels the retina and RPE/Cho proteome, accompanied by altered metabolic specialization between the two tissues.

biochemistry↗

bioRxiv2026

Exosomal Profiling Reveals Mechanisms of Hibernation-Associated Neuroprotection

Glaucoma is a group of eye diseases that affects 4 million people in the US and is one of the leading causes of vision loss due to damage to the eyes optic nerve (ON) which is composed of axons from retinal ganglion cells (RGCs) that transmit visual information to the brain. Injury to the ON often triggers RGC death and subsequent loss of visual function. Despite its increasing prevalence worldwide, effective therapies for glaucoma remain elusive. Notably, the thirteen-lined ground squirrel (TLGS) exhibits intrinsic neuroprotection during hibernation; however, reproducing this protective state pharmacologically has proven challenging. To elucidate the metabolic mechanisms underlying this resilience, we conducted untargeted metabolomic analyses on TLGS retinas at 6 hours, 3 days, and 7 days following ON crush. Retinas from awake and hibernating animals were compared to identify temporal and state-dependent metabolic signatures. Distinct metabolomic profiles were observed in hibernating animals relative to their awake counterparts. Pathway analyses revealed coordinated regulation of amino acid, lipid, and purine metabolism that likely contributes to hibernation-induced resilience. Furthermore, our findings indicate that hibernating TLGS retinas increase exosome biogenesis, prompting in vitro validation using TLGS-derived exosomes, which demonstrated robust neuroprotective and anti-inflammatory effects. Proteomic and transcriptomic characterization of exosomal cargo identified conserved miRNAs, mRNAs, and proteins implicated in redox balance, cytoskeletal stabilization, and stress-response regulation. Collectively, these data support the hypothesis that metabolic reprogramming and exosome-mediated intercellular signaling underlie hibernation-associated neuroprotection. Modulating these pathways may provide a blueprint for novel therapeutic strategies to mitigate neurodegeneration and promote recovery following optic nerve injury. Graphical AbstractIllustration depicting state-dependent metabolic responses to optic nerve crush (ONC) injury in Thirteen-lined Ground Squirrels (TLGS). In Awake animals, injury triggers enhanced ATP production through the TCA cycle, leading to excessive reactive oxygen species (ROS) generation and subsequent retinal ganglion cell (RGC) death. In contrast, Hibernating animals shift toward lipid metabolism and utilize ATP for the biosynthesis of ceramides and sphingolipids, promoting membrane integrity and exosomal signaling. Additionally, a range of metabolites associated with hibernation-linked neuroprotection are elevated, contributing to enhanced RGC survival. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/733742v1_ufig1.gif" ALT="Figure 1"> View larger version (81K): org.highwire.dtl.DTLVardef@1ef3a7eorg.highwire.dtl.DTLVardef@e9293dorg.highwire.dtl.DTLVardef@192729forg.highwire.dtl.DTLVardef@1a32cb5_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2026

Metabolic Intervention with Dimethyl Malonate Impairs Phagocytic Clearance but Fails to Protect Neurons

Secondary degeneration following optic nerve crush (ONC) is driven in part by mitochondrial dysfunction and microglial activation. Inspired by hibernation, where reduced succinate oxidation limits reactive oxygen species (ROS) production, we tested whether pharmacological inhibition of this pathway confers neuroprotection. Using in vivo ONC models and in vitro microglial assays, we evaluated the effects of dimethyl malonate (DMM), an inhibitor of succinate dehydrogenase, and a cell-permeable succinate analog (succinate-NV). Succinate-NV increased pro-inflammatory cytokine expression (IL-1{beta}) and reduced anti-inflammatory IL-10, whereas non-permeable succinate had no effect, indicating that intracellular succinate can drive microglial activation. In hibernating animals, succinate-NV disrupted neuroprotection and reduced retinal ganglion cell (RGC) survival following optic nerve injury. Although DMM partially reduced select inflammatory cytokines, it failed to normalize IL-1{beta} or IL-10 and suppressed microglial phagocytosis while exhibiting cytotoxic effects. In vivo, DMM-treated animals showed reduced IBA1{square} microglia but increased CD68{square} activation and accumulation of DAPI{square} cells at 7 days post-injury at the crush site. RGC somas persisted but were Caspase3+ consistent with impaired clearance. Astrocyte reactivity increased at lesion borders, while reduced and fragmented GFAP at the lesion site indicated localized astrocyte loss. Collectively, these findings demonstrate that inhibition of succinate oxidation alone is insufficient for neuroprotection and underscore the need for coordinated metabolic and immune regulation that cannot be achieved through single-pathway pharmacological intervention.

cell biology↗

bioRxiv2026

Early proteomic signatures of Alzheimer`s disease in the retina and brain of 3xTg-AD mice

Visual dysfunction and retinal structural alterations often precede brain pathology and cognitive decline in Alzheimers disease (AD), yet the molecular basis of these early changes and their relationship to the brain pathology remain unclear. Here, we performed quantitative proteomic profiling of retina and brain from 1-month of age triple-transgenic (3xTg-AD) mice harboring human PS1M146V, APPSwe, and tauP301L mutations, preceding detectable morphological abnormalities. Proteomic analysis identified 92 significantly altered proteins in the retina and 130 in the brain, with eight overlapping proteins between tissues. These shared proteins included three hemoglobin subunits (HBB1, HBB2, A8DUK4) and five proteins involved in metabolic regulation and intracellular transport. In addition to individual protein changes, pathway analysis demonstrated that mitochondrial metabolism and intracellular transport were commonly dysregulated in both tissues. Brain proteome was characterized by broad changes in mitochondrial-associated proteins, including respiratory chain components and mitochondrial ribosomal subunits, as well as proteins related to autophagy and synaptic vesicle pathways. In contrast, the retinal proteome was characterized by downregulation of vision-related proteins, altered small molecule transporters, and a marked reduction of the mitochondrial enzyme succinate-CoA ligase subunit {beta} (SUCB2). As SUCB2 links mitochondrial metabolism to epigenetic regulation through succinylation and lactylation, its depletion may promote mitochondria-to-nucleus signaling and early transcriptional reprogramming in the AD retina. Together, these findings demonstrate early metabolic and transport dysregulation in both retina and brain and highlight selective alterations of visual proteins in the retina. These early retinal proteomic changes provide valuable insight into understanding early metabolic disturbances in the eye and brain for AD detection.

biochemistry↗

bioRxiv2023

Proline provides a nitrogen source in the retinal pigment epithelium to synthesize and export amino acids for the neural retina

It is known that metabolic defects in the retinal pigment epithelium (RPE) can cause degeneration of its neighboring photoreceptors in the retina, leading to retinal degenerative diseases such as age-related macular degeneration. However, how RPE metabolism supports the health of the neural retina remains unclear. The retina requires exogenous nitrogen sources for protein synthesis, neurotransmission, and energy metabolism. Using 15N tracing coupled with mass spectrometry, we found human RPE can utilize the nitrogen in proline to produce and export 13 amino acids, including glutamate, aspartate, glutamine, alanine and serine. Similarly, we found this proline nitrogen utilization in the mouse RPE/Cho but not in the neural retina of explant cultures. Co-culture of human RPE with the retina showed that the retina can take up the amino acids, especially glutamate, aspartate and glutamine, generated from proline nitrogen in the RPE. Intravenous delivery of 15N proline in vivo demonstrated 15N-derived amino acids appear earlier in the RPE before the retina. We also found proline dehydrogenase (PRODH), the key enzyme in proline catabolism, is highly enriched in the RPE but not the retina. The deletion of PRODH blocks proline nitrogen utilization in RPE and the import of proline nitrogen-derived amino acids in the retina. Our findings highlight the importance of RPE metabolism in supporting nitrogen sources for the retina, providing insight into understanding the mechanisms of the retinal metabolic ecosystem and RPE-initiated retinal degenerative diseases.

biochemistry↗

bioRxiv2022

Isocitrate dehydrogenase 3b is required for spermiogenesis but dispensable for retinal degeneration

Isocitrate dehydrogenase 3 (IDH3), a key enzyme in mitochondrial tricarboxylic acid (TCA) cycle, catalyzes the decarboxylation of isocitrate into -ketoglutarate (KG), converting NAD+ into NADH. We have found that IDH3 {beta} subunit (IDH3B) is essential for IDH3 activity in multiple tissues. Loss of Idh3b in mice causes substantial accumulation of the isocitrate and its precursors in the TCA cycle, particularly in the testes, whereas the levels of the downstream metabolites remain unchanged or slightly increased. The Idh3b-knockout (KO) mice have normal visual function without retinal degeneration. However, the male KO mice are infertile. Loss of Idh3b causes energetic deficit and disrupts the biogenesis of acrosome and flagellum, resulting in spermiogenesis arrestment in sperm cells. Together, we demonstrate IDH3B controls its substrate levels in the TCA cycle and it is required for sperm mitochondrial metabolism and spermiogenesis, highlighting the importance of the tissue-specific function of the ubiquitous TCA cycle.

biochemistry↗