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Customer Article | Sci. Adv. | Jinhao Sun’s Team at Shandong University Unveils: How Does the Brain “Remember” Gastric Inflammation? Hcn1-Dependent PVN Engram Neurons Are the Key!

Release time：2026-06-10 14:37:37

Beyond local factors such as Helicobacter pylori infection and drug-induced irritation, bidirectional brain–immune regulation and psychological stress are critical triggers of gastritis. Clinically, gastritis often recurs even after H. pylori eradication, suggesting the presence of central inflammatory memory (central inflammation sensitization), though the underlying mechanisms remain unclear. The paraventricular nucleus of the hypothalamus (PVN), as a hub for neuroendocrine and autonomic integration, had an undefined role in gastritis regulation.

On May 15, 2026, Jinhao Sun’s team from the School of Basic Medical Sciences at Shandong University published a study titled Hcn1-dependent engram neurons in the PVN encode gastric inflammatory sensitization in Science Advances. This research focuses on the central neural mechanisms by which the brain regulates gastritis, revealing the pivotal roles of PVN Fos-positive neurons (Fos^PVN neurons) and the ion channel Hcn1 in stress–gastritis interactions, providing new targets for chronic inflammatory diseases.

https://doi.org/10.1126/sciadv.aeb6961

Activation of Fos^PVN Neurons in an HCl/Ethanol-Induced Gastritis Model

In an HCl/ethanol-induced mouse gastritis model, severe gastric mucosal hemorrhage and disrupted cellular architecture were observed 3 hours after induction (Fig. 1A–D), accompanied by significantly elevated levels of IL-1β and TNF-α in gastric tissues (Fig. 1E). To identify neurons activated during gastritis, the researchers used Fos-CreER^T2 × Rosa-TdT mice, in which 4-hydroxytamoxifen (4-OHT) induced the nuclear translocation of Cre recombinase, permanently labeling neurons activated within a specific time window (Fig. 1F). This approach was combined with retrograde polysynaptic tracing through gastric wall injection of PRV-CAG-EGFP pseudorabies virus (Fig. 1G). Whole-brain imaging revealed co-localization of EGFP- and Fos-TdT-positive neurons across multiple brain regions, with the highest overlap observed in the paraventricular nucleus of the hypothalamus (PVN), followed by the parasubthalamic nucleus (PSTh) (Fig. 1H, I). c-Fos immunofluorescence further confirmed that gastritis-induced neuronal activation was most prominent in the PVN and secondarily in the PSTh (Fig. 1J, K). Together, these findings demonstrate that gastritis selectively activates neurons in the PVN and PSTh, a subset of which directly or indirectly innervate the gastric wall.

Figure 1. Specific Activation of Fos^PVN Neurons in a Gastritis Model

Functional Role and Activation Mechanism of Fos^PVN Neurons in Gastritis

To investigate how gastritis regulates PVN neuronal activity, GCaMP6s was injected into the PVN and fiber photometry-based calcium imaging was performed (Fig. 2A). Three hours after gastritis induction, both the amplitude and frequency of calcium signals in PVN neurons were significantly increased (Fig. 2B–D), indicating enhanced neuronal activity. Using a Tet-Off system to label gastritis-activated Fos^PVN neurons and drive the expression of chemogenetic effectors (Fig. 2E, F), inhibition of gastritis-activated Fos^PVN neurons markedly reduced Fos expression within the PVN and alleviated gastric mucosal inflammation (Fig. 2G–L). Optogenetic inhibition further confirmed that suppressing this neuronal population significantly improved gastric mucosal injury (Fig. 2M–Q). In contrast, inhibition of Fos^PSTh neurons produced only modest anti-inflammatory effects.

Figure 2. Fos^PVN Neurons Regulate Gastritis

Mechanisms by Which Fos^PVN Neurons Regulate Gastritis

Immunofluorescence analysis showed that Fos^PVN neurons were predominantly corticotropin-releasing hormone (CRH)-positive neurons. Following gastritis induction, CRH expression in the PVN was significantly increased, accompanied by elevated plasma corticosterone levels (Fig. 3A–C). Intraperitoneal administration of the CRH receptor antagonist antalarmin markedly reduced gastric inflammation (Fig. 3D–G), suggesting that Fos^PVN neurons regulate gastritis through the hypothalamic–pituitary–adrenal (HPA) axis.

Electrophysiological recordings revealed that the firing frequency of gastric-innervating nerves was significantly elevated in gastritis mice (Fig. 3H, I). Retrograde tracing from the gastric wall combined with immunohistochemistry demonstrated that these neurons were primarily cholinergic neurons located in the dorsal motor nucleus of the vagus (DMV) (Fig. 3J, K). Furthermore, axonal terminals of gastritis-activated Fos+ neurons in the PVN co-localized with gastric wall retrograde tracing signals in the DMV (Fig. 3L, M), providing anatomical evidence for a Fos^PVN–DMV–stomach neural circuit.

To verify functional connectivity within this circuit, a mixture of AAV-DIO-ChR2-GFP and Fos-CreER^T2 viruses was injected into the PVN, and optical fibers were implanted above the DMV (Fig. 3N). Following gastritis induction and 4-OHT labeling, optogenetic stimulation of Fos^PVN axon terminals in the DMV significantly increased the firing frequency of gastric nerves in the ChR2 group (Fig. 3O, P), confirming functional connectivity of the circuit. In a conditioned place aversion (CPA) assay, optogenetic activation of Fos^PVN neurons induced environmental aversion behavior in mice (Fig. 3Q, R), suggesting a role in the regulation of negative emotional states.

Figure 3. Fos^PVN Neurons Regulate Gastritis Through the HPA Axis and Validation of the Fos^PVN–DMV Circuit

Further investigation of the Fos^PVN–DMV circuit demonstrated that optogenetic inhibition of Fos^PVN axon terminals within the DMV alleviated gastric inflammation and reduced gastric nerve firing frequency without affecting corticosterone levels (Fig. 4A–H). Conversely, activation of these terminals induced mild gastritis and enhanced gastric nerve activity, while similarly producing no changes in corticosterone or circulating inflammatory cytokine levels (Fig. 4I–O). Collectively, these findings indicate that Fos^PVN neurons regulate gastritis through two complementary pathways: the Fos^PVN–DMV–stomach neural circuit and the HPA axis.

Figure 4. Fos^PVN Neurons Regulate Gastritis Through the Fos^PVN–DMV Circuit

Repeated Activation of Fos^PVN Neurons Induces Chronic Gastritis

To investigate the effects of sustained abnormal activation of Fos^PVN neurons on chronic gastritis, rAAV-F-RAM-d2tTA-hM3Dq-mCherry was bilaterally injected into the PVN of mice. Two weeks after viral expression, gastritis was induced and Fos-positive neurons activated during this period were labeled. After a 3-week recovery period, mice were intraperitoneally injected with either CNO or saline on days 2–5 (Fig. 5A). In the saline group, Fos-positive PVN neurons rapidly declined after gastritis induction (minimal expression at 24 h, almost gone at 48 h). In contrast, CNO-mediated activation of Fos^PVN neurons maintained high Fos expression for an extended period (still abundant at 48 h and 96 h) (Fig. 5B, C).

In the experimental group, gastric wall structure was disrupted, inflammatory cytokines, corticosterone, and gastric nerve firing were significantly elevated, with no notable differences between 48 h and 96 h (Fig. 5D–I), suggesting that Fos^PVN neuron activation primarily initiates inflammatory responses rather than delaying recovery. After complete resolution of gastritis, optogenetic activation of Fos^PVN neurons for 5 consecutive days in the activation group resulted in disordered gastric wall cell arrangement, increased inflammatory cytokines, and enhanced gastric nerve firing, while serum inflammatory markers remained unchanged (Fig. 5J–O). Overall, repeated activation of Fos^PVN neurons specifically induces persistent chronic gastritis, mainly via local inflammatory responses rather than systemic inflammation.

Figure 5. Repeated Activation of Fos^PVN Neurons Induces Chronic Inflammation

snRNA-seq Identifies Hcn1 as a Key Regulatory Factor of Fos^PVN Neurons

Single-nucleus RNA sequencing (snRNA-seq) was performed on PVN tissue from control and gastritis mice (Fig. 6A). PVN neurons were classified into 15 subpopulations, and Fos-positive neurons were further subdivided into 13 subpopulations (Fig. 6B, C). Heatmaps showed marker genes for each subpopulation (Fig. 6D), with significant differences in subpopulation proportions between the two groups (Fig. 6E). Differentially expressed genes were involved in multiple biological processes. Among the top 30 differentially expressed genes, Hcn1 and CRH were significantly upregulated in gastritis mice (Fig. 6F), with the proportion of Hcn1 co-localized in CRH neurons increasing from 38% in controls to 53% in gastritis (Fig. 6G, H).

Figure 6. snRNA-seq Analysis Identifies Differentially Expressed Gene Hcn1

Immunofluorescence confirmed that both Hcn1 expression and Hcn1–CRH co-localization were significantly increased in gastritis mice (Fig. 7A–D). Injection of the Hcn1 inhibitor RO-275 into the PVN (Fig. 7E) markedly alleviated gastritis (Fig. 7F–I), and significantly reduced plasma corticosterone, gastric nerve firing, Fos expression in the PVN, and calcium activity (Fig. 7J–Q). Collectively, these results indicate that Hcn1 is a critical regulator of Fos^PVN neuronal activity.

Figure 7. Hcn1 Is a Key Regulatory Factor of Fos^PVN Neurons

Stress Exacerbates Gastritis via Fos^PVN Neurons

Water-immersion restraint stress (RS) was used to investigate the effect of stress on gastritis (Fig. 8A). RS mice exhibited anxiety-like behavior, gastric mucosal hemorrhage, disrupted cell arrangement, increased gastric inflammatory cytokines, elevated corticosterone levels, and enhanced gastric nerve firing, along with pronounced PVN neuronal activation (Fig. 8B–J). Using Fos-CreER^T2 × Rosa-TdT mice combined with PRV retrograde trans-synaptic tracing from the gastric wall, RS was shown to strongly activate Fos^PVN neurons and increase their projections to the gastric wall (Fig. 8K–M).

Figure 8. RS Induces PVN Neuronal Activation

Comparing the overlap between stress- and gastritis-activated neurons, both water-immersion restraint stress and social defeat stress (SDS) reactivated approximately 80% of gastritis-associated Fos^PVN neurons (Fig. 9A–D), suggesting that psychological stress can reactivate gastritis-encoding circuits. Inhibition of Fos^PVN neurons during stress reduced gastric inflammation (Fig. 9E–I). Immunofluorescence showed that Hcn1 expression was upregulated in stressed mice (Fig. 9J, K), and PVN-targeted Hcn inhibition alleviated stress-induced gastritis while reducing corticosterone levels and gastric nerve firing (Fig. 9L–R). Together, these findings indicate that water-immersion restraint stress exacerbates gastric inflammation by activating Fos^PVN neurons.

Figure 9. Stress Exacerbates Gastritis via Activation of Fos^PVN Neurons

Summary

This study systematically demonstrates that Fos^PVN neurons bidirectionally regulate gastritis through both the neuroendocrine HPA axis and the PVN–DMV–stomach neural circuit. Chronic activation of these neurons induces inflammatory sensitization and promotes the progression of chronic gastritis. Hcn1 serves as a key regulatory molecule, and psychological stress can reactivate these neurons to exacerbate inflammation. These findings provide new insights and experimental evidence for understanding the central regulation of gastric inflammation and for developing targeted therapies for chronic gastritis.

Tools Used in This Study (Available from Brain Case Biotech)

Product Category	Product Number	Product Name
Calcium Imaging	BC-0077	rAAV-hSyn-GCaMP6s
Chemogenetics	BC-2434	rAAV-F-RAM-d2tTA-TRE-hM3D(Gq)-mCherry
Optogenetics	BC-0107	rAAV-EF1α-DIO-hChR2(H134R)-EYFP
Optogenetics	BC-0125	rAAV-EF1α-DIO-eNpHR3.0-EYFP
Fluorescent Proteins	BC-2640	rAAV-F-RAM-d2tTA-TRE-mCherry
Recombinases	BC-3390	rAAV-cFos-iCre-ERT2
Retrograde trans-synaptic	BC-PRV-531	PRV-CAG-EGFP

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Customer Article | Sci. Adv. | Jinhao Sun’s Team at Shandong University Unveils: How Does the Brain “Remember” Gastric Inflammation? Hcn1-Dependent PVN Engram Neurons Are the Key!

Activation of Fos^PVN Neurons in an HCl/Ethanol-Induced Gastritis Model

Functional Role and Activation Mechanism of Fos^PVN Neurons in Gastritis

Mechanisms by Which Fos^PVN Neurons Regulate Gastritis

Repeated Activation of Fos^PVN Neurons Induces Chronic Gastritis

snRNA-seq Identifies Hcn1 as a Key Regulatory Factor of Fos^PVN Neurons

Stress Exacerbates Gastritis via Fos^PVN Neurons

Summary

Tools Used in This Study (Available from Brain Case Biotech)

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Customer Article | Sci. Adv. | Jinhao Sun’s Team at Shandong University Unveils: How Does the Brain “Remember” Gastric Inflammation? Hcn1-Dependent PVN Engram Neurons Are the Key!

Activation of FosPVN Neurons in an HCl/Ethanol-Induced Gastritis Model

Functional Role and Activation Mechanism of FosPVN Neurons in Gastritis

Mechanisms by Which FosPVN Neurons Regulate Gastritis

Repeated Activation of FosPVN Neurons Induces Chronic Gastritis

snRNA-seq Identifies Hcn1 as a Key Regulatory Factor of FosPVN Neurons

Stress Exacerbates Gastritis via FosPVN Neurons

Summary

Tools Used in This Study (Available from Brain Case Biotech)

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