The research team started from a simple but consequential observation: aging is accompanied by progressive functional decline and morphological defects in cholinergic neurons, the nerve cells that use the neurotransmitter acetylcholine and whose degeneration is a hallmark of disorders such as Alzheimer’s disease. Because the human gut harbors between 10^13 and 10^14 bacteria comprising at least a thousand different species, and because bacterial metabolites can enter the circulation and cross the blood-brain barrier, the so-called microbiota-gut-brain axis has become a major focus of research into both neuroprotection and neurological disease. Lowered biodiversity and dysbiosis of the gut microbiota have been documented in elderly people and in patients with Alzheimer’s and Parkinson’s disease, raising the question of whether specific probiotic bacteria might counteract these changes.

Biofilms were central to the investigation. These are complex three-dimensional structures of adherent, cooperative bacterial communities embedded in a secreted extracellular matrix, and growth within them helps bacteria survive hostile environments. Previous work in rodent and C. elegans models had identified biofilm proficiency as a crucial determinant of both pro- and anti-neurodegenerative actions of gut bacteria. In particular, neuroprotective effects of probiotic B. subtilis strains have been linked to biofilm formation in the gut and the release of biofilm-derived metabolic and signaling factors. Some B. subtilis strains also secrete proteolytic enzymes, including the fibrin-degrading enzyme nattokinase first isolated from the Japanese food natto, which can degrade amyloid fibrils characteristic of Alzheimer’s disease.

To find the most promising candidate, the researchers screened several B. subtilis strains in vitro for biofilm production and fibrinolytic activity. The proprietary strain B4U 50, deposited at the German Collection of Microorganisms and Cell Cultures as DSM 34350, was grown for 24 hours at 37 degrees Celsius in a simulated-colonic-environment medium in 96-well plates, after which attached biofilms were stained with crystal violet and quantified spectrophotometrically. B4U 50 developed extensive biofilms under these sessile growth conditions, clearly outperforming the widely used laboratory strain NCIB3610, which showed only modest biofilm formation, while the strains 168 and JH642 produced none. On fibrin agar plates, B4U 50 also displayed the highest fibrinolytic activity of the four strains tested, generating the largest transparent hydrolysis halos, whereas strain 168 showed no detectable fibrinolytic activity at all. The biofilm- and protease-deficient strain 168 therefore served as the control in all subsequent feeding experiments.

The experimental animal was the transgenic nematode strain LX929, in which cholinergic neurons are labeled with green fluorescent protein, allowing researchers to watch neuronal aging unfold in living animals. C. elegans offers distinct advantages for this kind of work: the worms nourish on bacteria, some ingested bacteria survive to become part of their gut flora, key longevity and stress-response pathways are evolutionarily conserved between worm and human, the nervous system contains only 302 well-characterized neurons, and the animals’ transparency and short lifespan permit rapid, longitudinal evaluation of dietary interventions. In aging nematodes, cholinergic neurons undergo progressive damage without cell loss, a process that mirrors the progressive dendritic, axonal and synaptic degeneration of cholinergic neurons seen in aging humans.

Synchronized worms were fed from their first larval stage for up to 15 days on either B4U 50 or the control strain 168, and their neurons were imaged by fluorescence microscopy on days 3, 7, 11 and 15. Three blinded researchers classified the neurons into three categories: normal neurons showed a continuous, uniform GFP signal along the ventral nerve cord; mildly damaged neurons displayed scattered minor swellings or knots without breaks in fluorescence; and severely damaged neurons showed multiple large swellings or visible ruptures in the nerve cord. From these categories the team calculated a neurodegeneration index, a composite score obtained by weighting normal, mildly damaged and severely damaged neurons with values of 0, 1 and 2 respectively.

The results were striking. Neuronal damage increased progressively with age in all groups, but the decline was markedly more pronounced in worms kept on the control strain: by days 11 and 15 these animals showed a steep drop in the proportion of normal neurons and a higher incidence of both mild and severe defects. Worms continuously fed B4U 50 retained a greater proportion of morphologically intact neurons throughout the observation period, and their neurodegeneration index remained significantly lower. The team also ran dietary switch experiments, transferring worms initially raised on strain 168 to B4U 50 on day 4, day 8 or day 12. Switching early, on day 4, produced a neuroprotective effect comparable to continuous feeding with B4U 50; switching on day 8 still conferred a moderate benefit; but switching on day 12 no longer protected the neurons. This defines a window of early and middle adulthood for optimal dietary intervention.

The researchers also tested whether the bacterial diet could be combined with a known neuroprotective compound. They used TEBONIN intens, a standardized extract prepared from Ginkgo biloba leaves, which has been reported to enhance cognitive performance in patients with mild and moderate dementia and to extend lifespan and alleviate amyloid-beta-induced pathology in C. elegans models. Supplementation with the Ginkgo biloba preparation was neuroprotective in worms fed on either B. subtilis strain, reducing both the occurrence and the timing of mild and severe neuronal defects. Notably, the combination of B4U 50 and the Ginkgo biloba extract yielded the highest proportion of morphologically intact neurons by day 15 and the lowest neurodegeneration index values of any group, while worms on the control strain without the extract fared worst. Representative fluorescence images of day-15 animals made the difference visible: worms receiving the combined intervention displayed largely intact GFP-labeled ventral nerve cords, whereas those fed only the control strain exhibited pronounced swellings and discontinuities.

Why might a biofilm-forming bacterium protect nerve cells? The authors point to a proposed model in which B. subtilis spores ingested with food survive gastric transit, germinate in the intestine, and grow in biofilms that produce and secrete substances spreading from the gut throughout the body, exerting anti-aging and neuroprotective effects. Previous studies have identified the quorum-sensing pentapeptide known as competence sporulation-stimulating factor and the gasotransmitter nitric oxide as key mediators of the benefits of B. subtilis biofilms, and probiotic biofilm-producing strains have been shown to counteract neurodegeneration in wild-type worms as well as in transgenic models of Alzheimer’s and Parkinson’s disease expressing human amyloid-beta and alpha-synuclein. Metabolic remodeling during biofilm development is complex, affecting cellular respiration, lipid metabolism and the production of secondary metabolites and signaling molecules.

The authors are careful about the limits of their work. They did not examine whether B4U 50 actually forms a biofilm inside the worm gut, nor did they identify the specific signaling or metabolic factors mediating the neuroprotective effect, and they note this as a limitation of the study. It is also worth noting that the research was funded by Evonik Operations GmbH, the company that maintains the proprietary B4U 50 strain, and that three of the co-authors are Evonik employees, though the other authors report no competing interests. Nevertheless, the study extends a promising line of research suggesting that B. subtilis strains with strong biofilm proficiency, whether laboratory strains like NCIB3610 or probiotic isolates from East Asian fermented foods, can extend lifespan and protect the nervous system in C. elegans. If the findings translate beyond the nematode, combining biofilm-proficient probiotic bacteria with established natural products such as standardized Ginkgo biloba extract could yield dietary supplements with enhanced neuroprotective capacity for the prevention and amelioration of neurodegenerative disorders.

Subject of Research: Neuroprotective effects of a biofilm-forming Bacillus subtilis probiotic strain on aging cholinergic neurons in C. elegans

Article Title: A Bacillus subtilis strain with high proficiency for biofilm formation delays the onset of aging-associated morphological defects in cholinergic neurons of C. elegans

Article References: Gong, W., Priebs, J., Ohse, V. A., Bremges, A., Dieck, H. T., Klotz, L.-O., Dargatz, M., & Steinbrenner, H. (2026). A Bacillus subtilis strain with high proficiency for biofilm formation delays the onset of aging-associated morphological defects in cholinergic neurons of C. elegans. GeroScience. https://doi.org/10.1007/s11357-026-02594-0

Image Credits: AI Generated

DOI: 10.1007/s11357-026-02594-0

Keywords: Bacillus subtilis, C. elegans, biofilm, cholinergic neurons, neurodegeneration, probiotics, Ginkgo biloba, microbiota-gut-brain axis, aging, nattokinase, neuroprotection, GeroScience

The neurons in question produce acetylcholine, a chemical messenger that is critical for a range of functions including sleep, cognition and movement. Their gradual loss is linked to some of Parkinson’s most disabling and treatment-resistant symptoms: problems with gait and balance, disturbed sleep, cognitive decline and, in some people, psychosis. While much of the public and scientific attention on Parkinson’s has centred on dopamine-producing neurons in the midbrain, which underlie the condition’s characteristic tremor, rigidity and slowness of movement, this study shifts focus to a brainstem population whose decline shapes the broader, often harder-to-treat burden of the illness.

To interrogate these cells, the team used advanced single-cell mitochondrial DNA sequencing combined with computational analysis, examining individual neurons from brain tissue generously donated by people who had lived with Parkinson’s disease, alongside tissue from healthy controls. Rather than averaging signals across thousands of cells, the single-cell approach allowed the researchers to read out the mitochondrial genome of each neuron separately, revealing the extent and pattern of damage cell by cell. Dr Ilse Pienaar of the University of Birmingham, a senior author of the study, noted that this is the first time single-cell mitochondrial genetic sequencing has been applied to these specific brainstem neurons in people with Parkinson’s disease, and that studying individual neurons has allowed the team to see, in unprecedented detail, the mitochondrial changes associated with their vulnerability.

What the sequencing revealed was striking. The affected neurons carried extensive large-scale deletions in their mitochondrial DNA, and these deletions were particularly concentrated within a stretch of the mitochondrial genome known as the major arc. This region is densely populated with genes that are essential for producing energy in cells, so removing chunks of it strikes directly at the machinery that keeps a neuron powered. Mitochondria are often described as the powerhouses of the cell, and damage to their DNA can interfere with their ability to generate the energy that neurons need, potentially leaving these cells less able to cope with the relentless electrical and metabolic demands placed on them across a human lifetime.

The biological logic of this vulnerability is compelling. Neurons are among the most energy-hungry cells in the body, and brainstem cholinergic neurons must sustain long projections and continuous signalling to regulate sleep-wake cycles, attention and motor control. If their mitochondrial genomes accumulate deletions in the very region that encodes core components of the energy-production system, the resulting power deficit could compound over time, gradually eroding the cell’s capacity to survive. The new findings therefore provide a mechanistic account of why these acetylcholine-producing neurons may be particularly susceptible to degeneration in Parkinson’s disease, complementing decades of work on dopaminergic cell loss.

Yet the study is not simply a catalogue of damage. Despite the extensive mitochondrial DNA lesions, the researchers found evidence that the neurons may be mounting an active protective response. The affected cells showed increased levels of PINK1, a gene central to mitochondrial quality control. PINK1 helps cells identify mitochondria that have become damaged and target them for removal, a process that clears dysfunctional power units from the network and helps maintain a population of healthy mitochondria capable of sustaining energy production. In other words, even as the mitochondrial genomes of these neurons crumbled, the cells appeared to be ramping up the molecular machinery that weeds out the worst-affected organelles.

Perhaps the most intriguing observation concerns individual variation. Higher levels of PINK1 were particularly evident in neurons from people who had survived longer after their Parkinson’s diagnosis. This pattern raises the possibility that a stronger mitochondrial quality-control response helps some neurons withstand damage for longer, effectively buying time and preserving function in the face of accumulating genetic injury. If confirmed, the finding would suggest that the trajectory of Parkinson’s disease is shaped not only by the forces that damage neurons but also by the variable vigour of the brain’s own defences against that damage.

Dr Joanna Elson of Newcastle University, a senior author of the study, described the results as revealing an extraordinary resilience within these vulnerable neurons. Although the team observed extensive mitochondrial DNA damage, the cells appear to mount a protective response through increased PINK1 expression, likely as an attempt to maintain healthy mitochondria and preserve energy production. She added that understanding why this response appears to be more effective in some individuals than others could open new avenues for therapies aimed at supporting the brain’s own protective mechanisms. Dr Pienaar similarly emphasised that the findings point towards biological pathways that could potentially be harnessed therapeutically, and that strengthening the mechanisms which maintain mitochondrial health could ultimately help slow disease progression and improve quality of life for people living with Parkinson’s.

The therapeutic implications are considerable. PINK1 has long been known to the Parkinson’s field because mutations in the gene cause early-onset, inherited forms of the disease, placing it at the heart of the cellular pathway that surveys mitochondrial health and dispatches damaged organelles. The new data suggest that this same pathway is active in the vulnerable brainstem neurons of people with sporadic Parkinson’s, and that its activity correlates with survival after diagnosis. That correlation makes mitochondrial quality control an attractive target for drug development: if researchers can identify why the response is more effective in some patients and find ways to amplify it in others, treatments might be developed that enhance the brain’s natural protective mechanisms rather than simply replacing lost neurotransmitters.

The researchers hope the findings will catalyse further studies of mitochondrial quality-control pathways as potential therapeutic targets in Parkinson’s disease, and that understanding how some neurons withstand damage could ultimately inform treatments that bolster these defences across the brain. For a condition that affects millions worldwide and for which current therapies address symptoms rather than halt progression, the demonstration that single-cell sequencing can expose both the vulnerabilities and the resilience of individual human neurons marks a methodological and conceptual advance. It reframes Parkinson’s disease, in part, as a struggle between mitochondrial damage and cellular self-repair, one in which the outcome may depend on how well each neuron can keep its power supply intact.

Subject of Research: Single-cell mitochondrial DNA sequencing of vulnerable brainstem cholinergic neurons in Parkinson's disease

Article Title: First study to sequence mitochondrial DNA from individual vulnerable brainstem neurons in Parkinson’s disease

Article References: First study to sequence mitochondrial DNA from individual vulnerable brainstem neurons in Parkinson’s disease. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Parkinson's disease, mitochondrial DNA, single-cell sequencing, brainstem neurons, PINK1, cholinergic neurons, mitochondrial quality control, neurodegeneration, major arc deletions, Brain journal, University of Birmingham, Newcastle University

A research team led by Qianqian Li, Jiale Chen, and Miao Ren of the Hainan University collaboration with the HUST-Suzhou Institute for Brainsmatics dissected specific subregions of the mouse basal forebrain, midbrain, and brainstem in both adult animals aged three to five months and aged animals aged eighteen to twenty-four months. Using the 10x Genomics Chromium platform, they generated single-nucleus RNA sequencing libraries and, after rigorous quality control, assembled an atlas of 108,062 high-quality cells. Computational annotation based on canonical marker genes identified eleven major cell types, including GABAergic and glutamatergic neurons, cholinergic neurons, oligodendrocytes and their precursors, microglia, astrocytes, endothelial cells, ependymal cells, pericytes, and fibroblasts. Reference-based label transfer with Seurat confirmed the assignments with high concordance, giving the team a reliable cellular census across three anatomically and functionally distinct cholinergic territories.

The first striking finding came from comparing how entire brain regions respond to age at the multicellular level. In the aged basal forebrain, upregulated differentially expressed genes were consistently enriched across multiple cell types in pathways tied to p53-mediated inflammatory responses, oxidative phosphorylation, synaptic translation, and protein synthesis. No comparable coordinated transcriptional activation appeared in the aged midbrain or brainstem. Meanwhile, genes downregulated with age in all three regions clustered around axon guidance and neuronal maintenance. In other words, the basal forebrain undergoes a robust, brain-wide transcriptional remodeling characterized by heightened stress and metabolic programs alongside erosion of the pathways that keep neurons structurally intact, a pattern conspicuously absent from its more resilient neighbors.

To probe how cells talk to one another, the researchers applied CellChat, a computational framework that infers intercellular communication from ligand-receptor expression. The analysis revealed a striking regional specificity. The ApoE signaling pathway, a major genetic risk factor for Alzheimer’s disease, was active exclusively in the basal forebrain, where microglia acted as the principal receivers of ApoE signals emitted by cholinergic neurons and other cell types. The aged brainstem instead showed specific activation of insulin-like growth factor signaling, a change the authors interpret as a potentially protective or compensatory mechanism supporting metabolic homeostasis and survival. The aged midbrain displayed enhanced protocadherin signaling, associated with neuronal identity and connectivity. These distinct signaling landscapes suggest that each cholinergic system ages within its own extracellular milieu, shaped by different glial and metabolic partners.

One pathway, however, spanned all three regions: amyloid precursor protein, or APP, signaling, with cholinergic neurons identified as the putative receiver cells. Here the regional differences proved decisive. In the basal forebrain and midbrain, the importance of APP signaling to cholinergic neurons rose substantially with age, driven largely by the App-Tnfrsf21 ligand-receptor pair, whereas the brainstem showed no such age-related increase. Given that APP processing lies at the heart of amyloid-beta generation in Alzheimer’s disease, the selective amplification of APP reception in aged basal forebrain cholinergic neurons hints at an extracellular signaling context that may prime these cells for degeneration. The finding dovetails with recent work showing that aging selectively increases the vulnerability of the cholinergic system to amyloid pathology.

Zooming in on the cholinergic neurons themselves, unbiased subclustering revealed that they segregate cleanly by anatomical origin, forming the most regionally distinctive transcriptional profile of any cell type in the atlas. Basal forebrain cholinergic neurons highly expressed Lhx8, Ngfr, and Ntrk1, the latter two encoding receptors for nerve growth factor, a trophic signal long known to sustain these cells. Midbrain neurons were enriched for Tgfbr2, Egflam, and Nos1, while brainstem neurons expressed Sv2b, Ryr3, and Nfia. RNAscope in situ hybridization validated the star of this list: Ngfr was expressed in nearly all basal forebrain cholinergic neurons and virtually absent from the midbrain and brainstem populations. Functional enrichment underscored the divide, with basal forebrain genes tied to neurodegenerative disease pathways and synaptic signaling, midbrain genes to nitric oxide and Wnt signaling, and brainstem genes to longevity-regulating and PI3K-Akt pathways.

High-dimensional weighted gene co-expression network analysis then exposed how aging rewrites these programs differently in each region. In the basal forebrain, an age-correlated module was enriched in neurodegenerative disease pathways, oxidative phosphorylation, ATP biosynthesis, and apoptotic signaling, and contained the aging-linked genes Malat1 and Ube3a. The midbrain’s age module pointed instead toward RNA processing, nuclear transport, and chromatin remodeling, while the brainstem’s declining module involved neuronal migration, axon guidance, and neurotransmitter transport. Gene set variation analysis confirmed the asymmetry: stress and apoptosis pathways climbed in aged basal forebrain cholinergic neurons, whereas metabolic homeostasis and growth signaling pathways, including insulin receptor recycling and IGF1 signaling, rose in the midbrain and brainstem while falling in the basal forebrain.

Differential expression between adult and aged cholinergic neurons within each region revealed remarkably little overlap, with 186 genes uniquely upregulated and 92 uniquely downregulated in the aged basal forebrain, and hundreds of region-specific changes in the brainstem but none in the midbrain. The basal forebrain losses were especially telling, encompassing axonal and cytosolic transport, neurotrophic signaling, lipid membrane metabolism, and the somatic and synaptic architecture that keeps a neuron connected. The brainstem, by contrast, upregulated gene sets for ion homeostasis, energy metabolism, cytoskeletal maintenance, and cell survival, an adaptive profile consistent with resilience. Two genes with opposite regional trajectories stood out. Oxr1, a conserved antioxidant protein that protects mitochondria and guards against oxidative damage, rose with age in basal forebrain cholinergic neurons and fell in the brainstem. Ptprs, a receptor tyrosine phosphatase governing axon growth, adhesion, and synapse formation, dropped in the basal forebrain and trended upward in the brainstem.

Using the machine-learning framework scTenifoldKnk, the team simulated virtual knockouts of these two candidates in basal forebrain cholinergic neurons. Perturbing Oxr1 disrupted 81 downstream genes, including 22 that were both age-related and hub genes of the oxidative stress module, with enrichment in the ERK1/2 cascade, synapse assembly, and neuron projection extension. Virtual knockout of Ptprs perturbed 69 genes, among them neurodevelopmental regulators such as Nfib and Reln, converging on axon guidance, synaptic organization, and neurotransmitter cycling. Both perturbations thus struck the same target: the gene networks that maintain neuronal structure and synaptic function. The authors are careful to note the caveats. Tissues from multiple mice were pooled per library, limiting replicate-level statistics; both sexes were combined, precluding assessment of sex-specific effects; and the findings remain transcriptomic predictions awaiting experimental validation in living models. Many brainstem cholinergic neurons are also motor neurons with fundamentally different physiological demands, which may partly explain their apparent resilience. Even so, the study delivers a compelling molecular framework for one of neuroscience’s enduring questions: why the neurons that sustain our memory and attention are precisely the ones that time attacks first, and where, in their shifting gene networks, the seeds of that vulnerability lie.

Subject of Research: Region-specific molecular mechanisms underlying selective aging vulnerability of cholinergic neurons in the mouse basal forebrain, midbrain, and brainstem

Article Title: Single-nucleus transcriptomics uncovers region-specific molecular features underlying selective aging vulnerability of cholinergic neurons

Article References: Li, Q., Chen, J., Liu, X., Gong, H., Li, X., & Ren, M. (2026). Single-nucleus transcriptomics uncovers region-specific molecular features underlying selective aging vulnerability of cholinergic neurons. iScience, 29(11), Article 117778. https://doi.org/10.1016/j.isci.2026.117778

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117778

Keywords: cholinergic neurons, basal forebrain, single-nucleus RNA sequencing, brain aging, Alzheimer's disease, ApoE signaling, APP signaling, Oxr1, Ptprs, neurodegeneration, CellChat, transcriptomics