Scientists Found a New Abnormality Inside Human Glaucoma Nerve Cells — Could It Lead to a New Treatment?

This audio article is from VisualFieldTest.com.Read the full article here: https://visualfieldtest.com/en/scientists-found-a-new-abnormality-inside-human-glaucoma-nerve-cells-could-it-lead-to-a-new-treatmentTest your visual field online: https://visualfieldtest.comSupport the show so new episodes keep coming: https://www.buzzsprout.com/2563091/supportExcerpt:Scientists Found a New Abnormality Inside Human Glaucoma Nerve Cells — Could It Lead to a New Treatment? Short answer: Possibly—but the evidence is still early. A newly published human donor-retina study found that glaucoma was associated with less sphingomyelin inside retinal ganglion cells, more acid sphingomyelinase protein, and greater activity of the lysosomal form of that enzyme. The study also found more retinal ganglion cells containing ceramide aggregates, although total ceramide was not significantly higher overall. That pattern is biologically interesting because acid sphingomyelinase can break down sphingomyelin into ceramide. Excessive or mislocalized ceramide can disturb lysosomes, cell membranes, autophagy, mitochondria, inflammatory signaling, and programmed cell death. However, the human study is observational and postmortem. It does not prove that acid sphingomyelinase starts glaucoma or that inhibiting it will preserve vision. The strongest evidence for causality still comes from animal and cell studies, not from patients. > My overall interpretation: Acid sphingomyelinase is a credible contributor to retinal ganglion-cell injury in at least a subset of glaucoma, but it is unlikely to be the only cause or a universal treatment target. --- What the New Human Study Actually Found The newest study, published online on August 31, 2026, examined donated human retinas from people with and without a glaucoma diagnosis. It used a sphingomyelin-binding probe called enhanced green fluorescent protein-conjugated non-toxic lysenin and identified retinal ganglion cells using the retinal ganglion-cell marker RNA-binding protein with multiple splicing. The researchers also measured acid sphingomyelinase, neutral sphingomyelinase, sphingomyelin synthase 1, sphingomyelin synthase 2, enzyme activity, and ceramide distribution. Human glaucoma donor-retina study () What can be determined from the currently accessible report? For the full table, please open this article on visualfieldtest.com. The article is currently labeled an early accepted version that may undergo further editing before the final version of record. Therefore, exact numeric values should be taken from the full downloadable article and supplementary data once they are accessible in a stable form, rather than reconstructed from figures or secondary summaries. Scientific Reports article page () The most important negative finding The study did not show a simple, uniform increase in total ceramide throughout the retina. That matters. A straightforward model would predict: > More acid sphingomyelinase → less sphingomyelin → more total ceramide. Instead, the study found: > Less sphingomyelin in retinal ganglion cells → more acid sphingomyelinase → more ceramide-containing aggregates, but no statistically significant increase in total retinal ganglion-cell ceramide. This suggests that the important abnormality may be local ceramide clustering, rather than a large increase in the average ceramide concentration across the whole retina. That is biologically plausible because ceramide can act as a membrane-organizing signal. A small amount concentrated in the wrong lysosomal or plasma-membrane domain may be more damaging than a larger amount dispersed throughout the cell. --- Why the Study Is Interesting but Not Yet Proof of Cause The human findings support a coherent mechanism, but several alternative explanations remain possible. Acid sphingomyelinase may increase because retinal ganglion cells are already dying Damaged neurons often activate lysosomal enzymes, inflammatory pathways, and membrane-recycling systems. Therefore, increased acid sphingomyelinase could be: an early cause of retinal ganglion-cell injury; a response to mechanical, vascular, or metabolic injury; or a late consequence of degeneration. The human study cannot determine the timing because postmortem tissue provides only one snapshot. Lower sphingomyelin may partly reflect cell loss Glaucomatous retinas contain fewer retinal ganglion cells. A whole-retina dot blot can therefore show lower sphingomyelin simply because the tissue contains fewer sphingomyelin-rich neurons. The cell-level analysis is stronger because it compares sphingomyelin labeling in identified retinal ganglion cells. Even then, survivor bias remains possible: the analysis may compare surviving glaucoma retinal ganglion cells with healthy cells while missing the most severely damaged cells that have already disappeared. The lysenin probe does not measure every sphingomyelin species equally Enhanced green fluorescent protein-conjugated lysenin preferentially binds certain, especially longer-chain, sphingomyelin species. It is therefore best interpreted as a measure of accessible membrane-associated sphingomyelin, not necessarily a complete measurement of every sphingomyelin molecule in the cell. Visualizing sphingomyelin in the retina () Postmortem tissue is vulnerable to artificial biochemical changes Important limitations include: postmortem delay, which can alter lysosomal pH and enzyme activity; hypoxia or agonal illness before death; systemic infection, diabetes, vascular disease, or inflammation; cause of death; age and sex differences; glaucoma medications; antidepressant or antihistamine exposure; retinal region sampled; fixation and tissue-processing differences; incomplete removal of vitreous or other surrounding tissue; loss of fragile or already-degenerated cells; uncertainty about the exact glaucoma subtype and severity. These factors are particularly important because acid sphingomyelinase is a stress-responsive enzyme. --- Reconstructing the Proposed Pathway The proposed pathway is: > Acid sphingomyelinase activation → sphingomyelin breakdown → ceramide generation and clustering → lysosomal and membrane dysfunction → mitochondrial stress → apoptosis → retinal ganglion-cell and axon loss Each step has a different level of evidence. Step 1: Acid sphingomyelinase activation Acid sphingomyelinase is encoded by the SMPD1 gene. Its main form is located inside lysosomes, where it works best in an acidic environment. A separate form can be processed and secreted outside the cell. The lysosomal form is often described as the zinc-independent pool, whereas secreted acid sphingomyelinase is more dependent on zinc at neutral extracellular pH. The new human study found increased retinal ganglion-cell acid sphingomyelinase expression and increased zinc-independent activity, while the secretory pool did not significantly change. That pattern points toward an intracellular lysosomal abnormality rather than a generalized rise in circulating or extracellular enzyme. Step 2: Sphingomyelin breakdown Acid sphingomyelinase converts sphingomyelin into: ceramide; phosphorylcholine. Sphingomyelin is not merely structural fat. It contributes to: plasma-membrane stability; membrane thickness and order; lipid-raft organization; receptor signaling; lysosomal membrane properties; vesicle trafficking. The 2022 retinal and optic-nerve-head study found that sphingomyelin species were concentrated in the retinal ganglion-cell layer, optic nerve, and choroidal regions. In experimental ocular hypertension, retinal acid sphingomyelinase activity increased from approximately 54.98 mU/mg protein at baseline to 121.6 mU/mg protein, about a 2.2-fold increase. In the optic nerve head, activity increased from approximately 95.6 to 267.0 mU/mg protein, about a 2.8-fold increase. Sphingomyelinases in retinas and optic nerve heads () Step 3: Ceramide accumulation and clustering Ceramide is a signaling lipid, not simply a waste product. Depending on its chain length, location, and concentration, ceramide can: promote membrane-domain formation; cluster death receptors; alter calcium handling; impair vesicle trafficking; affect lysosomal stability; stimulate inflammatory signaling; disrupt mitochondrial membranes; activate caspases and apoptosis. The new human glaucoma study suggests that ceramide aggregation in selected retinal ganglion cells may be more important than total retinal ceramide. This would explain why whole-tissue lipidomics may fail to detect a large increase: the damaging signal may be concentrated in a small number of vulnerable cells. Step 4: Lysosomal and autophagy dysfunction Lysosomes must maintain a precise lipid composition. Too much sphingomyelin can impair lysosomal function, but too little acid sphingomyelinase can also be harmful. This is demonstrated by acid sphingomyelinase-deficient mice. Complete deletion caused: progressive photoreceptor degeneration; reduced electroretinogram responses; retinal pigment epithelium dysfunction; lipofuscin accumulation; abnormal sphingomyelin and sphingosine accumulation; increased autophagosome-associated protein. Lack of acid sphingomyelinase induces age-related retinal degeneration () This is a critical warning: complete acid sphingomyelinase blockade is not a safe therapeutic goal. The likely goal would be partial, localized, and disease-stage-specific reduction. Step 5: Mitochondrial stress Retinal ganglion cells are highly energy-dependent neurons with long axons. Mitochondrial dysfunction is an established earlySupport the show