A new Johns Hopkins study links the loss of a brain enzyme responsible for producing hydrogen sulfide — famously known as “fart gas” — to memory decline and Alzheimer’s-like brain damage in mice. This discovery could open new therapeutic pathways for treating neurodegenerative diseases by targeting the CSE enzyme pathway rather than symptom management.
Researchers at Johns Hopkins Medicine have identified a single brain enzyme — cystathionine γ-lyase (CSE) — as central to memory function. The enzyme generates tiny amounts of hydrogen sulfide (H2S), a gas notorious for its rotten egg odor, within neurons. The findings, published in Proceedings of the National Academy of Sciences (PNAS), suggest that maintaining normal levels of H2S signaling via CSE may be crucial for preventing age-related cognitive decline and neurodegeneration.
The team led by associate professor Bindu Paul studied genetically engineered mice lacking the CSE enzyme. These mice exhibited progressive memory loss beginning at six months of age, while performing normally at two months. The decline was not due to movement problems or general health issues — their locomotion, weight, and sensory functions remained intact. Instead, the deficit pointed squarely toward a neurodegenerative process.
Why Hydrogen Sulfide Matters
Hydrogen sulfide is one of several chemical messengers in the brain that regulate stress responses, protein function, and cell survival. While three enzymes — CSE, CBS, and 3-MST — can produce H2S in the brain, scientists previously believed CBS and 3-MST were the primary sources. CSE, mostly found in neurons, has long been overlooked outside neurological contexts.
Paul’s group argues that focusing solely on CBS and 3-MST misses critical roles played by CSE. The enzyme shapes H2S signaling in ways that influence synaptic proteins, oxidative stress control, and neuron survival. There’s also a delicate balance: too little H2S impairs brain function; too much causes toxicity. This makes drug development challenging — simply delivering H2S to the brain is risky. Instead, future therapies may aim to restore optimal low-level signaling without triggering toxicity.
A Clear Behavioral Signal
To isolate CSE’s impact, researchers used the Barnes maze test — where mice learn to find an escape hole under bright light. At two months, both wild-type and CSE-lacking mice performed similarly. By six months, however, the knockout mice struggled significantly, indicating a progressive onset of neurodegeneration attributable specifically to CSE loss.
Co-first author Sunil Jamuna Tripathi emphasized the scope of impairment: “The mice lacking CSE were compromised at multiple levels, which correlated with symptoms that we see in Alzheimer’s disease.” The team ruled out simple explanations like motor dysfunction or sensory deficits — confirming that the observed changes were purely cognitive.
Damaged Hippocampus Reveals Alzheimer’s Biomarkers
The hippocampus — a brain region vital for learning and memory — showed multiple signs of damage in CSE-deficient mice. Researchers detected elevated oxidative stress, DNA damage, and weakened blood-brain barrier integrity. Proteomic surveys revealed shifts in proteins tied to synapses and transport, alongside increased markers of lipid damage and DNA lesions.
Specifically, the dentate gyrus — a subregion of the hippocampus involved in neurogenesis — displayed decreased expression of doublecortin (DCX), a marker of immature neurons. Stem cell division markers also declined, leading to fewer newborn neurons surviving over time. These changes mirror early hallmarks of Alzheimer’s disease biology.
Leaky Barriers and Fewer New Neurons
Using high-powered electron microscopes, researchers observed structural damage to the blood-brain barrier (BBB) in CSE-lacking mice — a key protective layer that normally restricts harmful substances from entering the brain. Immune proteins such as IgG leaked into brain tissue, suggesting compromised barrier integrity.
Neurogenesis — the birth of new neurons — also declined sharply. Markers of immature neurons dropped, stem cell division slowed, and fewer newborn neurons survived. Since neurogenesis naturally declines with age and neurodegenerative diseases, these findings suggest CSE is essential for maintaining neuronal regeneration.
CREB and BDNF: The Molecular Links
Researchers connected these changes to established pathways tied to memory formation. They reported weaker activation of CREB — a transcription factor critical for turning on genes needed for learning — and alterations in BDNF, a well-known molecule supporting synaptic plasticity. These molecular disruptions align with Alzheimer’s pathology.
Practical Implications for Alzheimer’s Therapy
More than 6 million people in the United States currently live with Alzheimer’s disease — a number projected to rise dramatically. This study does not offer a cure, but it identifies a potential upstream target: the CSE enzyme pathway. Unlike traditional approaches focused on symptom suppression, this research suggests strategies aimed at preserving brain resilience — such as boosting CSE activity or stabilizing its signaling — without risking toxic exposure to hydrogen sulfide.
The findings also point toward possible biomarkers for early detection. Changes in blood-brain barrier integrity, iron handling, and neurogenesis could serve as indicators of early-stage neurodegeneration before full-blown symptoms appear. That could allow for earlier intervention and more effective therapies designed to slow decline.
What This Means for Future Research
If similar biology is confirmed in humans — which remains to be tested — CSE could become a major focus for drug development. The challenge will be designing compounds that safely modulate CSE activity without disrupting other cellular processes. The study also opens avenues for exploring how H2S signaling interacts with existing Alzheimer’s therapeutics.
As co-corresponding author Solomon Snyder noted, “This most recent work indicates that CSE alone is a major player in cognitive function and could provide a new avenue for treatment pathways in Alzheimer’s disease.” His lab’s prior work linking CSE to brain protection in Huntington’s models further supports its significance across neurodegenerative conditions.
While the research remains preliminary — conducted exclusively in mice — its implications are profound. If validated in human studies, this could shift the field’s approach from reactive symptom management to proactive preservation of neural function.
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