PANoptosis is a relatively recent concept in cell biology. Rather than treating inflammatory cell death as a set of separate pathways, researchers have come to view pyroptosis, apoptosis, and necroptosis as deeply intertwined, with shared molecular machinery forming a large complex known as the PANoptosome. That complex, assembled from proteins such as RIP1, RIP3, and NLRP3 in response to damage signals, executes a death program that is simultaneously inflammatory, self-dismantling, and membrane-rupturing. PANoptosis has been documented in heart injury, retinal ischemia, glaucoma, and lung damage, but whether it occurs in neurons after a mild knock to the brain had remained an open question. The new study provides some of the clearest evidence yet that it does.

Using a controlled cortical impact model in mice calibrated to produce mild injury, the researchers first tracked Snapin expression over time. Protein levels in the injured cortex climbed significantly within twelve hours and stayed elevated for roughly three days, with a similar but slightly delayed rise in the hippocampus. Immunofluorescence staining one day after injury revealed that the upregulated Snapin was concentrated almost exclusively in neurons, co-localizing with the neuronal marker NeuN far more than with markers of microglia or astrocytes. This neuronal specificity mattered, because it pointed the finger at the cells whose loss underlies the cognitive and motor decline that follows concussion.

To test whether Snapin was merely a bystander or an active participant, the team used adeno-associated viruses to deliver a short hairpin RNA that silenced Snapin specifically in the injured brain region. The results were striking. Twenty-four hours after injury, when cell death peaks, mice with reduced Snapin showed significantly lower levels of the full PANoptosis toolkit: pyroptosis markers including NLRP3, caspase-1, gasdermin D, ASC, and interleukin-1 beta; apoptosis markers including caspase-3 and Bax; and necroptosis markers RIP1 and RIP3. Double-label imaging confirmed that fewer neurons carried caspase-3, gasdermin D, or RIP1 signals. Silencing Snapin also reduced degenerating neurons on Nissl and Fluoro-Jade B stains and preserved brain tissue volume at twenty-eight days.

The behavioral consequences were equally compelling. Injured mice with Snapin knockdown recovered grip strength faster on the wire-grip test, moved less anxiously in the open field, performed better on novel object recognition, and navigated the Morris water maze with shorter escape latencies and more platform crossings than injured controls. Reduced activation of astrocytes and microglia around the injury site suggested that dampening the cell death program also quieted the neuroinflammatory aftermath. Interestingly, the story was not simply that less Snapin is always better: in uninjured sham animals, Snapin silencing actually increased some degeneration, indicating that the protein performs essential housekeeping duties under healthy conditions and only turns destructive in the altered chemistry of the injured brain.

That chemistry centers on hydrogen sulfide, the pungent gas better known for its rotten-egg smell but increasingly recognized as a versatile signaling molecule in the nervous system. Hydrogen sulfide is synthesized by three enzymes, including cystathionine beta-synthase, or CBS, and it modifies proteins through a post-translational reaction called S-sulfhydration, which attaches sulfur to cysteine residues and can alter protein activity. The Soochow team found that after mild brain injury, Snapin physically interacts with CBS, an interaction confirmed by co-immunoprecipitation and supported by molecular docking simulations that predicted a stable complex with a favorable binding score. Yet despite elevated CBS expression, tissue hydrogen sulfide levels fell after injury, and silencing Snapin partially restored them. Blocking hydrogen sulfide synthesis with aminooxyacetic acid erased the protective effect of Snapin knockdown, placing the gas firmly downstream of Snapin in the pathway.

The downstream target turned out to be cathepsin D, or CTSD, the dominant aspartate protease of the brain’s lysosomes, accounting for roughly ninety percent of acidic protease activity there. CTSD is born as an inactive precursor, pro-CTSD, and must mature through the endosome-lysosome pathway into its active form. After mild injury, the researchers found that pro-CTSD levels were unchanged but mature CTSD surged, and mature CTSD escaping from leaky lysosomes is well positioned to trigger caspase-3 activation and apoptotic death. Crucially, the team’s modified biotin-switch assays showed that S-sulfhydration of pro-CTSD dropped after injury, and that hydrogen sulfide treatment restored this modification while simultaneously reducing mature CTSD accumulation. In other words, sulfur modification of the precursor acts as a brake on CTSD maturation, and the injured brain loses that brake.

To confirm that the mature protease was the executioner, the researchers administered pepstatin A, a CTSD inhibitor, or sodium hydrosulfide, a hydrogen sulfide donor, immediately after injury. Both interventions reduced mature CTSD, suppressed the entire PANoptosis marker panel, cut the number of degenerating neurons, and improved long-term outcomes. Treated mice showed better motor scores on wire-grip and beam-balance tests, less anxiety-like behavior, improved recognition and spatial memory, greater preserved hemisphere volume at twenty-eight days, and fewer activated microglia and astrocytes. The convergence of a protease inhibitor and a gas donor on the same outcome strengthens the causal chain from Snapin through hydrogen sulfide and CTSD maturation to neuronal death.

The emerging picture is one of a compensatory response gone wrong. The authors propose that Snapin rises after injury as part of an attempt to shore up synaptic and lysosomal function, consistent with its known roles in endosome-lysosome trafficking and autophagosome-lysosome fusion. But in the redox-impaired environment of the injured brain, where sulfur metabolism falters, that same elevation disrupts hydrogen sulfide homeostasis, weakens S-sulfhydration of pro-CTSD, accelerates CTSD maturation, and ignites PANoptosis. Snapin thus undergoes a functional shift from homeostatic guardian to accomplice in neuronal loss, a context-dependent duality that may explain why broadly suppressing such proteins is risky while timed, injury-specific intervention appears beneficial.

The clinical implications are tantalizing but preliminary. Concussion affects millions of people each year, and the persistent translational gap in traumatic brain injury research reflects both the heterogeneity of clinical phenotypes and incomplete understanding of secondary cell death. A defined axis, Snapin to hydrogen sulfide to CTSD to PANoptosis, offers multiple points of potential intervention, from modulating Snapin-CBS interaction to boosting sulfur modification of lysosomal enzymes. Notably, prior clinical work has found CTSD gene upregulation in salivary extracellular vesicles of patients with mild traumatic brain injury, hinting at biomarker potential. The mouse findings, behavioral windows limited to the acute and subacute phases, and the dual role of Snapin in healthy neurons all caution against premature translation. Still, the study adds a striking entry to the growing list of gasotransmitter-controlled switches in the brain, and it suggests that the aftermath of a mild head injury may one day be tamed by chemistry as simple as sulfur.

Subject of Research: The role of Snapin, hydrogen sulfide signaling, and cathepsin D maturation in neuronal PANoptosis after mild traumatic brain injury

Article Title: Snapin mediates neuronal PANoptosis after mild traumatic brain injury via H 2 S-dependent S-sulfhydration of CTSD

Article References: Chen, X., Huang, X., An, Y., Gao, C., Gao, Y., Shan, H., Tao, L., Chen, X., & Zhang, M. (2026). Snapin mediates neuronal PANoptosis after mild traumatic brain injury via H2S-dependent S-sulfhydration of CTSD. Journal of Advanced Research, 88, 911-927. https://doi.org/10.1016/j.jare.2026.01.039

Image Credits: AI Generated

DOI: 10.1016/j.jare.2026.01.039

Keywords: mild traumatic brain injury, PANoptosis, Snapin, hydrogen sulfide, cathepsin D, S-sulfhydration, CBS, lysosomes, neurodegeneration, neuroinflammation, programmed cell death, concussion

MASLD has become one of the most common chronic liver conditions in the pediatric population, tracking closely with the global rise in childhood obesity. The disease involves the abnormal accumulation of fat within liver cells and, in a subset of patients, can progress to inflammation, fibrosis, and eventually cirrhosis. The challenge for clinicians is that the liver is remarkably silent in its early stages: children with accumulating hepatic fat typically feel well, and standard liver enzymes such as alanine aminotransferase can remain within normal limits even when fat infiltration is well established. The current diagnostic gold standard, liver biopsy, is rarely justified in children because of its invasiveness, cost, and sampling variability. Abdominal ultrasound is the usual screening tool, but it is operator-dependent and loses sensitivity when hepatic fat content is modest. This diagnostic gap is precisely what the Chinese team set out to address.

The researchers, led by Huanyu Wang and Zongming Yang of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, with corresponding authors Shimin Wu and Xiaoping Luo, conducted a cross-sectional study of children with obesity who presented to the hospital’s Department of Pediatrics between January 2023 and September 2024. The final analysis included 84 children, 53 boys and 31 girls, of whom 43—just over half—were diagnosed with MASLD based on abdominal ultrasound findings. Each child underwent anthropometric assessment, including body mass index z-score and waist-to-height ratio, alongside fasting metabolic panels. The team then quantified serum concentrations of five candidate biomarkers using enzyme-linked immunosorbent assays: cathepsin D, leptin, adiponectin, insulin-like growth factor 1, and growth differentiation factor 15.

These five molecules were not chosen at random. Each represents a distinct biological axis implicated in obesity-related liver disease. Cathepsin D is a lysosomal protease involved in intracellular protein degradation, and emerging evidence links it to lipid metabolism, insulin signaling, and hepatic inflammation. Leptin, the prototypical adipocyte-derived hormone, signals energy stores to the brain and participates in immune and fibrotic pathways in the liver. Adiponectin, another adipokine, is generally insulin-sensitizing and anti-inflammatory, and its levels tend to fall as metabolic health deteriorates. Insulin-like growth factor 1 mediates growth hormone action and is often altered in states of insulin resistance. Growth differentiation factor 15 is a stress-responsive cytokine of the transforming growth factor beta superfamily that rises in mitochondrial stress and systemic inflammation, and it has attracted attention as a broad marker of cardiometabolic risk.

The statistical approach was deliberately conservative. Rather than simply asking whether biomarker levels differed between children with and without MASLD, the investigators calculated odds ratios across tertiles of each biomarker after adjusting for established risk factors: age, sex, body mass index z-score, and waist-to-height ratio. This adjustment matters because any marker that merely reflects the degree of obesity adds little clinical value; the question was whether these proteins carry independent information about liver fat beyond what a clinician already knows from measuring a child’s size. The team also tested the shape of each association, allowing for nonlinear relationships rather than assuming a straight line.

The results were striking for cathepsin D. Children in the highest tertile of logarithmically transformed serum CTSD had roughly twelve-fold higher odds of MASLD compared with those in the lowest tertile, with an odds ratio of 12.63 and a 95 percent confidence interval spanning 2.57 to 84.62, and the association was linear across the distribution. Growth differentiation factor 15 also showed a robust positive association: children in the top tertile had nearly five times the odds of MASLD relative to the bottom tertile, with an odds ratio of 4.86 and a confidence interval of 1.14 to 23.57. Leptin told a more nuanced story. After full adjustment, its relationship with MASLD risk was inverse U-shaped, meaning risk peaked at intermediate leptin concentrations rather than rising monotonically. Children in the middle tertile had an odds ratio of 6.70 compared with the lowest tertile, and the test for nonlinearity yielded a p-value of 0.004. Adiponectin and insulin-like growth factor 1, by contrast, lost any significant independent association once conventional risk factors were accounted for.

Association alone, however, does not make a biomarker clinically useful. The researchers therefore asked whether adding each protein to a base prediction model containing age, sex, BMI z-score, and waist-to-height ratio actually improved diagnostic performance. They evaluated this with three complementary metrics: the area under the receiver operating characteristic curve, which measures overall discrimination; the continuous net reclassification improvement, which quantifies how many patients are moved into more accurate risk categories; and the integrated discrimination improvement, which assesses gains in predicted probabilities. Individually, each biomarker produced only marginal and statistically non-significant increases in the optimism-corrected AUC—for example, adding cathepsin D yielded a change in AUC of 0.047 with a p-value of 0.096.

Yet the reclassification analyses told a more encouraging story. Incorporating cathepsin D produced the most prominent improvement in risk stratification, with a continuous net reclassification improvement of 1.147 (95 percent confidence interval 0.152 to 1.657, p = 0.032) and an integrated discrimination improvement of 0.142 (95 percent confidence interval 0.014 to 0.339, p = 0.008). Leptin and insulin-like growth factor 1 also generated significant reclassification gains, with all p-values below 0.05. In practical terms, this means that even when a biomarker does not dramatically shift the average discrimination statistic, it can still meaningfully re-sort individual children into more appropriate risk categories—correctly elevating the estimated risk of those who truly have hepatic steatosis and lowering it for those who do not. For a condition in which the decision to pursue further imaging or specialist referral hinges on risk thresholds, such reclassification can translate directly into better-targeted care.

The biological plausibility of the three signal-bearing markers strengthens the case. Cathepsin D’s strong association fits with its emerging role as a mediator of lysosomal lipid handling and inflammatory signaling in hepatocytes. The leptin finding is particularly intriguing: the inverse U-shaped curve suggests that both relatively low and very high leptin concentrations carry different risk implications than intermediate levels, a pattern that could reflect receptor desensitization, leptin’s dual roles in appetite regulation and hepatic fibrogenesis, or confounding by adiposity distribution that the adjustment model only partially captures. Growth differentiation factor 15’s positive association aligns with its established behavior as a marker of cellular metabolic stress, which would be expected to rise as hepatic fat accumulation imposes mitochondrial and inflammatory burdens on the liver.

The authors are careful to frame these results as preliminary. With only 84 participants, the confidence intervals are wide, and the odds ratios—especially the double-digit estimate for cathepsin D—carry substantial statistical uncertainty. The cross-sectional design also means the study captures a single snapshot; it demonstrates association, not causation, and cannot establish whether elevated cathepsin D or GDF15 precede the development of steatosis or accompany it. The single-center recruitment from one pediatric obesity clinic further limits generalizability, and ultrasound-based diagnosis, while standard in clinical practice, is an imperfect reference. The team explicitly calls for validation in larger, multicenter cohorts before these markers enter clinical decision-making. Still, the study was approved by the Tongji Hospital Ethics Committee and supported by China’s National Key Research and Development Program and the Natural Science Foundation of Hubei Province, and it offers a concrete, testable hypothesis: that a small panel of serum proteins, measured alongside routine anthropometry, could sharpen the non-invasive detection of MASLD in children. If larger studies confirm the reclassification gains observed here, pediatricians may one day identify which of their young patients with obesity carry silent liver disease with a routine blood test—catching, at an early and potentially reversible stage, a condition that otherwise hides in plain sight for decades.

Subject of Research: Serum cardiometabolic biomarkers for diagnosing metabolic dysfunction-associated steatotic liver disease in children with obesity

Article Title: Association and diagnostic value of serum cardiometabolic biomarkers for metabolic-associated steatotic liver disease in children with obesity

Article References: Wang, H., Yang, Z., Wu, S., Weng, Y., Hou, L., Wu, W., & Luo, X. (2026). Association and diagnostic value of serum cardiometabolic biomarkers for metabolic-associated steatotic liver disease in children with obesity. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07697-3

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07697-3

Keywords: MASLD, pediatric obesity, cathepsin D, leptin, GDF15, biomarkers, fatty liver disease, non-invasive diagnosis, risk stratification, ELISA, children, hepatic steatosis