◉ Colloquy — research, out loud
Scientific Reports · 2026 · doi:10.1038/s41598-026-65928-0
Abstract In various cancers, tumor suppressor neprilysin plays a crucial role in preventing tumorigenesis. Neprilysin levels are decreased cancers and neuronal disorders. the brain, NEP is expressed by astrocytes. However, with oncogenic markers glioblastoma has not been explored. this study, we investigated possible effects of progression on signalling using rat model. The western blot analysis PTEN, AKT, p53, Pro-caspase-3 VEGF-A, immunofluorescence GFAP, FAK, FGF-2, EGFR VEGFR-2 were performed. protein activity attenuated tissues as well cerebrum glioblastoma-induced animals, consistent reduced MME expression TCGA cohort. Hypoxia recognized contributor to downregulation, hypoxic histopathological regions associated elevated pro-caspase-3 expression. positively correlated PTEN p53 proteins, which also glioblastoma. addition, EGFR, GFAP surface expressions negatively neprilysin. Also, substrate- its downstream effector increased tissues. These correlations further supported human glioma transcriptomic data from TCGA, examining marker associations Within cohort, only , AKT1 showed significant study findings suggest that modulation may serve potential therapeutic strategy for
Researcher A When glioblastoma, the most aggressive brain tumor, takes hold, a protective enzyme called neprilysin drops dramatically—and the cancer's worst drivers surge. This study in rats shows that loss of this one enzyme tracks with the tumor's ability to escape control, raising a question: could restoring it fight back?
Researcher B Okay, so neprilysin is the hero here, and it's disappearing. But I'm guessing this is correlative, not causal—they're showing these things happen together, not that one causes the other?
Researcher A Exactly right. The authors are clear: they've mapped the landscape, not proven cause and effect. That's the honest catch.
Researcher B So what's the gap in the field? Why does neprilysin in glioblastoma matter now?
Researcher A Neprilysin—also called neutral endopeptidase or NEP—has been shown to suppress tumors in prostate, lung, breast, and other cancers. But until now, nobody had mapped what happens to neprilysin *during* glioblastoma progression in a living animal, or how it correlates with the key oncogenes and tumor suppressors that drive the disease.
Researcher B In other words, it's been studied in cell culture, but not in vivo, and not specifically in glioblastoma?
Researcher A Right. There were hints from U87 glioma cells in a dish, but the in vivo regulatory network—how neprilysin sits within the web of PTEN, AKT, p53, and all the pro-growth factors—that was uncharted.
Researcher B Walk me through the experiment.
Researcher A They used two approaches. First, they mined human data: they looked at MME gene expression—that's the gene that codes for neprilysin—across 667 glioma patients from the TCGA database, stratified by tumor grade and type. They also checked survival outcomes.
Researcher B And the animal work?
Researcher A They injected C6 rat glioma cells—one hundred thousand cells in ten microliters—directly into the cerebrum of adult male Wistar rats using a stereotaxic instrument. Three groups: normal controls, sham controls who got saline, and tumor-bearing rats. Twenty-five days later, they harvested brains and measured neprilysin protein levels, activity, and surface expression using Western blots and immunofluorescence. They also quantified PTEN, AKT, p53, VEGF-A, pro-caspase-3, FAK, FGF-2, EGFR, and VEGFR-2.
Researcher B Sample size?
Researcher A Ten animals per group initially; two died from tumor progression, leaving eight in the glioblastoma group. For Western blots they used n equals twelve, for immunofluorescence n equals twenty.
Researcher B So they did *not* do a therapeutic intervention—they didn't try to boost neprilysin and see if it slowed the tumor?
Researcher A Correct. This is a mapping study, not a treatment trial. They explicitly note that causation and therapeutic potential require further investigation.
Researcher B Okay, the key results. Give me numbers.
Researcher A In the human data: high MME expression was associated with significantly better overall survival. In the combined glioma cohort, patients with high MME had a median survival of seventy-five months versus thirty-four point nine months for low MME—a forty-month difference. Hazard ratio was one point eighty-five, p less than zero point zero zero one.
Researcher B That's striking. But glioblastoma alone?
Researcher A Interestingly, glioblastoma-specific analysis did *not* show significant survival difference. High MME median was eleven point three months, low was fourteen point nine months. The authors attribute this to the heterogeneity and smaller sample size of glioblastoma alone—n equals one hundred fifty.
Researcher B So the protective signal is clearer in lower-grade tumors?
Researcher A Or diluted by glioblastoma's molecular noise. Now, in the rat model: neprilysin activity dropped significantly in both cerebrum and tumor tissue. In the cerebrum, p equals zero point zero zero forty-seven; in tumor, p less than zero point zero zero zero five.
Researcher B And the correlations?
Researcher A Neprilysin showed positive correlation with tumor suppressors PTEN and p53—Spearman's rho equals zero point six nine nine three and zero point six zero one four respectively. But strong negative correlations with oncogenic drivers: AKT, VEGF-A, FAK, FGF-2, EGFR, VEGFR-2. VEGF-A had the strongest inverse correlation: rho equals negative zero point nine six five, p less than zero point zero zero zero one.
Researcher B That VEGF-A correlation is nearly perfect inverse. What about the quieter finding?
Researcher A Histopathology showed hypoxic regions in tumor tissue, and those hypoxic areas had elevated pro-caspase-3 and reduced neprilysin. The authors note that glioblastoma cells accumulate micromolar pools of inactive pro-caspase-3 as a resistance mechanism—they don't actually undergo apoptosis, they just accumulate the precursor. That's a subtlety most people miss.
Researcher B What does the paper itself flag?
Researcher A The authors are explicit: this is correlative, not causative. They write, 'the present study demonstrates significant correlations between NEP downregulations and multiple oncogenic pathways in glioblastoma; however, causative relationships and therapeutic potential require further investigation.' They also note they measured pro-caspase-3 protein abundance, not enzymatic activity, so they can't directly confirm the caspase-3 degradation pathway.
Researcher B What about the GFAP correlation? That seemed odd.
Researcher A Good catch. The elevated GFAP they see is mostly reactive astrogliosis—the brain's response to tumor presence and the injection trauma—not tumor cells themselves expressing GFAP. The authors acknowledge they lack single-cell double-labeling to definitively separate cell types. So the GFAP-neprilysin inverse correlation may be partly an artifact of spatial distribution rather than direct antagonism.
Researcher B Worth noting beyond the authors' list?
Researcher A The C6 rat model is well-established but it's a xenograft—not a spontaneous tumor. The tumor microenvironment may differ from human glioblastoma. Also, they used only male rats, so sex effects are unknown. And the human survival analysis is based on mRNA, not protein; the authors themselves note that glioblastoma shows a disconnect between transcriptome and proteome, with heavy post-translational modification. So the human MME signal may not fully predict neprilysin protein levels in actual tumors.
Researcher A Three audiences, I'd say. First: neuro-oncologists and glioblastoma researchers. The reason is this maps a potential new axis—neprilysin-PTEN-AKT—that's distinct from the usual EGFR and VEGF targets, and it's consistent across rat protein data and human transcriptomics.
Researcher B Second?
Researcher A Drug developers interested in neprilysin modulation. There are already neprilysin inhibitors in clinical use—sacubitril, for instance, used in heart failure. The question is: could upregulating neprilysin, or stabilizing it, be a glioblastoma strategy? This paper gives a rationale.
Researcher B And third?
Researcher A Researchers studying tumor suppressors and the PI3K-AKT pathway broadly. The PTEN-neprilysin-AKT axis may be relevant in other cancers too. The paper cites evidence from prostate cancer, and the mechanism—neprilysin stabilizing PTEN—could apply elsewhere.
Researcher A This is Sankhe, Reddy, Gopinathan, Begum, Pai, Upadhya, and Kishore, published in Scientific Reports, twenty twenty-six. The D O I is ten point one zero three eight, slash, s four one five nine eight, dash, zero two six, dash, six five nine two eight, dash, zero.
Researcher B And the thread is open on Colloquy.