Cutting Baseline Research Report in Nature Neuroscience: Pancreas–Hippocampus Feedback Mechanism Regulates Circadian Rhythm and Depression-Related Behaviors

1. Introduction and Academic Background

In recent decades, the comorbidity of neuropsychiatric disorders and metabolic dysregulation has become a research hotspot in neuroscience and psychiatric medicine. In particular, the high correlation between bipolar disorder (BD) and diabetes or insulin metabolic abnormalities (metabolic syndrome) has drawn widespread medical attention. It has been found that about 40% of patients with bipolar disorder present with diabetes or insulin metabolic symptoms. BD patients with coexistent metabolic dysregulation tend to show a chronic disease course, rapid mood fluctuations, and diminished responses to mood stabilizers. This suggests that metabolism–behavior interactive mechanisms might play a key role in the pathogenesis of bipolar disorder.

Insulin, as a key hormone in glucose metabolism, has its receptors (insulin receptor, InsR) not only widely distributed in peripheral organs but also in the hippocampus and cerebral cortex within the central nervous system. Previous studies have shown that abnormal insulin signaling can result in neuronal atrophy, cognitive impairment, and even neurodegeneration. In addition to pancreatic secretion, hippocampal neurons are also capable of secreting insulin, participating in the regulation of their own function and manifesting the complex physiological interaction between central and peripheral insulin pathways. However, the reverse question—how hippocampal neuronal activity may influence insulin secretion—remains unclear.

At the molecular level, RORβ (Retinoic acid-related orphan receptor β) functions as a circadian rhythm regulatory factor, believed to participate in the regulation of the biological clock and is linked to susceptibility to neuropsychiatric diseases such as bipolar disorder and epilepsy. However, RORβ’s precise physiological role in the pancreas, brain development, etc., has yet to be fully elucidated. Recent reports suggest aberrant expression of RORβ may be associated with β-cell dysfunction, but direct mechanistic evidence demonstrating its influence on mood and behavior is still lacking.

Based on the above background, this study aims to explore the role of RORβ in the pancreas–hippocampus feedback loop, clarify the molecular and neural circuit basis of metabolic and circadian behavioral fluctuations, and provide new insights into the pathogenesis of bipolar disorder.

2. Paper Source Information

This article was completed by Yao-nan Liu and colleagues, with authors affiliated with the School of Life Sciences at Tsinghua University, the Salk Institute in the United States, Beijing Tiantan Hospital, Affiliated Brain Hospital of Guangzhou Medical University, Beijing Institute of Genomics (Chinese National Center for Bioinformation), among other prestigious institutions. The paper was published in October 2025 in the top international journal Nature Neuroscience, titled “A pancreas–hippocampus feedback mechanism regulates circadian changes in depression-related behaviors.”

3. Detailed Research Procedure

1. Overall Research Design

This study utilizes multidisciplinary technical approaches, including human induced pluripotent stem cell (iPSC) disease modeling, organoid culture, molecular assays, multi-omics (RNA-seq), Western blotting, animal model gene editing (CRISPRa), behavioral testing, electrophysiology, chemogenetics, and optogenetics. These are applied to systematically elucidate how pancreatic RORβ expression regulates insulin secretion, hippocampal neural activity, and circadian behavioral fluctuation.

2. Clinical Sample Collection and iPSC Derivation

The team first collected skin fibroblasts from five patients each with bipolar II disorder (BDII), major depressive disorder (MDD), and five healthy controls (HCII), using Sendai virus reprogramming to generate iPSC lines. Additionally, six previously established bipolar I disorder (BDI) and four healthy control (HCI) iPSC lines were included. These iPSCs were used for downstream organoid differentiation studies.

3. Forebrain and Islet Organoid Modeling

Using a spinning bioreactor system, the iPSCs were differentiated into mature forebrain organoids, verifying the expression of deep- and upper-layer markers (CTIP2, TBR1, BRN2, SATB2) and intact electrophysiological function (Na+, K+ currents, AP firing). Quantitative analysis showed no significant differences in tissue thickness or neuron composition between patients and controls.

Next, using the latest differentiation protocols, iPSCs were induced to form islet-like organoids (containing β-like cells), confirmed by the expression of β-cell markers (C-peptide, NKX6.1) and the presence of insulin-secreting granules. Flow cytometry, immunofluorescence, and RT-qPCR verified a similar β-cell differentiation efficiency of about 20% across all groups.

4. Multi-Omics and Molecular Mechanism Screening

RNA sequencing (RNA-seq) on organoids identified disease-related differences in gene expression and signaling pathways. KEGG pathway analysis revealed that the insulin secretion pathway was abnormally regulated in BDII forebrain organoids and presented common features with BDI dentate gyrus (DG) neurons and BDII organoids, but not in MDD.

Molecular analyses of islet organoids found that iPSC-derived islet-like organoids from BDI and BDII patients had significantly reduced insulin mRNA (ins) and protein, with impaired insulin secretion—providing direct evidence of insulin secretion abnormalities in bipolar disorder.

5. RORβ Screening and Functional Verification

Screening for BD susceptibility genes using the Malacards database and analyzing their expression in forebrain and islet organoids revealed that RORβ is significantly upregulated in the islet organoids of BDI and BDII patients, but not in forebrain organoids, and its increase is restricted to β-like cells. RORβ mRNA in patient peripheral plasma was also found to be significantly elevated, whereas in postmortem brain tissues it was unchanged, indicating a disease-specific alteration in the periphery rather than the brain.

Using a CRISPRa system, the authors activated RORβ expression specifically in mouse pancreatic β-cells and verified that increased RORβ expression and mRNA remained restricted to the pancreas. Behavioral tests showed that such transgenic mice (sg1/sg2 group) exhibited an inverted circadian pattern of insulin secretion: whereas in normal mice insulin is higher during the day and lower at night, in sg1/sg2 mice, insulin is lower during the day and higher at night.

6. Behavioral Testing and Neural Circuit Investigation

Behaviorally, sg1/sg2 mice exhibited depression-like behaviors (e.g., increased immobility in forced swim test [FST], reduced sucrose preference) during the day, and mania-like behaviors (reduced immobility, increased sucrose preference) at night. Three-chamber social tests showed no significant change in social interaction, but social novelty preference was diminished.

Mechanistic probing using peripheral or intrahippocampal administration of insulin and an insulin receptor blocker (BMS-536924) revealed that insulin could reverse day-phase depression-like behaviors in sg1/sg2 mice, while central insulin receptor blockade deepened the behavioral phenotype. Notably, blocking brain insulin receptors unexpectedly activated pancreatic insulin secretion, suggesting feedback from the CNS to the periphery.

Optogenetic and chemogenetic experiments further demonstrated that manipulating hippocampal neural activity could directly alter pancreatic secretion and behavioral phenotypes. Activation (Chr2) or inhibition (NphR) of hippocampal neurons induced long-lasting circadian changes in insulin secretion and corresponding behavioral transitions. The VCA1-LHA projection in the hippocampus was also shown to play a role in regulating behaviors in sg1/sg2 mice.

4. Main Results and Logical Interpretation

1. Insulin Secretion Abnormalities in Human iPSC-Derived Islet Organoids Are Strongly Associated with Bipolar Disorder

iPSC-derived islet organoids from BD patients showed significantly reduced insulin secretion at baseline and after glucose stimulation, which was reversible with RORβ inhibitors or specific shRNA. This means that RORβ upregulation is a key molecular mechanism underlying insulin secretion deficits.

2. Aberrant RORβ Expression Causes a Reversal of the Circadian Rhythm of Insulin and Bidirectional Behavioral Feedback

Specific upregulation of RORβ in the pancreas reverses the circadian profile of insulin secretion—low during the day, high at night—in mice, closely mirroring behavioral rhythms. This circadian fluctuation is mapped onto hippocampal neuron spiking rates via the feedback mechanism. Low insulin levels facilitate hippocampal neuronal hyperactivity, which in the short term drives depression-like behavior, and in the long term promotes a compensatory increase in night-time insulin release, lowering hippocampal spiking and manifesting as mania-like behavior.

3. Verification of Central–Peripheral Feedback and Mechanistic Dissection

Blocking hippocampal insulin signaling can paradoxically promote pancreatic insulin secretion, and hippocampal neural activity modulates pancreatic signaling via the VCA1-LHA projection, establishing a complete feedback loop. Optogenetic and chemogenetic experiments confirm the neural basis of behavioral rhythm transitions and islet insulin secretion.

5. Conclusion and Evaluation

This work unveils a novel pancreas–hippocampus feedback mechanism, demonstrating that islet RORβ expression regulates circadian insulin secretion and subsequently drives hippocampal neural activity and behavioral cycles. This provides solid molecular, cellular, and systems neuroscience evidence for the metabolic and behavioral interplay seen in bipolar disorder and other neuropsychiatric conditions. The mechanism operates over both short-term (30 minutes to hours) and long-term (over 12 hours) intervals, and the feedback loop is substantiated using chemogenetics, optogenetics, behavioral, and transgenic mouse studies. This significantly expands the theoretical foundation for the interplay between metabolism and emotional neuroscience.

6. Scientific and Applied Value

1. Scientific Significance

• Reveals a novel molecular basis influencing circadian behavioral fluctuations: the RORβ-insulin–hippocampus circuit;
• First demonstration that peripheral pancreatic signaling can modulate its own secretion via CNS feedback, and hippocampal modulation of pancreatic signaling can reverse behavioral phenotypes;
• Expands the application of iPSC and organoid technologies in the study of psychiatric disease mechanisms, demonstrating the advantages of precise disease modeling.

2. Application Prospects

• Provides a mechanistic rationale for developing targeted therapies for bipolar disorder and psychiatric conditions with metabolic comorbidities, such as RORβ inhibitors and insulin sensitizers;
• Offers new avenues for precision medicine, behavioral intervention, and drug development;
• Lays a molecular foundation for identifying biomarkers for the screening of bipolar disorder.

7. Research Highlights

• Innovative use of the CRISPRa gene-editing system to achieve pancreas-specific activation of RORβ and generate a disease mouse model with reversed circadian rhythm;
• Combined use of iPSC-derived organoids and mouse models to robustly validate molecular pathology, strongly supporting the research conclusions;
• Comprehensive evidence from behavioral, electrophysiological, and molecular studies, constructing a complete pathological model from the cellular, organ, systems, and behavioral levels;
• Elucidation of the central–peripheral feedback circuit, filling a major gap in the study of metabolic–neuropsychiatric interaction mechanisms.

8. Other Noteworthy Findings

• The study suggests that in addition to RORβ, other BD-susceptibility genes related to the insulin pathway (such as Synaptotagmin-7) may also influence disease phenotypes, raising new avenues for mechanistic investigation;
• The data show that, despite limited sample sizes, there were significant inter-group differences, indicating the robustness of the findings;
• The study also implicates the involvement of the PI3K signaling pathway in insulin-related behavioral regulation, laying a foundation for future research.

9. Summary

This paper not only reveals, at the molecular and neural circuit levels, a cross-organ feedback mechanism between the pancreas and hippocampus, enriching knowledge of the interaction network between neuropsychiatric illness and metabolic disturbances, but also provides a solid theoretical basis and experimental paradigm for the individualized treatment, early warning, and mechanistic exploration of bipolar disorder in the future. As iPSC disease modeling and systems neuroscience techniques continue to converge, interdisciplinary perspectives like this are expected to drive breakthrough advances across a broad range of psychiatric disorders.