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Client Article | Neuron | Prof. Jingdun Xie’s Team at Sun Yat-sen University Decodes PDAC Comorbidity: How the Tumor–Metabolism–Neuron Axis Drives Pain and Depression

Release time：2025-12-16 11:13:54

Patients with pancreatic ductal adenocarcinoma (PDAC) often suffer from severe, difficult-to-control pain and comorbid depression, which markedly impair quality of life and survival. However, the central mechanisms underlying these comorbidities remain unclear. Neuro–tumor interactions and metabolic reprogramming play important roles in PDAC-associated comorbidity, yet the precise mechanisms by which they regulate neural dysfunction are still to be elucidated. N⁶-methyladenosine (m⁶A) modification and methyltransferase 14 (METTL14) have been implicated in cancer as well as in the regulation of pain and depression. S-adenosylmethionine (SAM), the key substrate for m⁶A methylation, also participates in cancer progression. Nevertheless, whether METTL14-mediated epigenomic modification in the central nervous system contributes to PDAC-induced comorbidities remains unknown.

On November 4, 2025, Prof. Jingdun Xie’s team at Sun Yat-sen University published a study in Neuron entitled “METTL14 integrates tumor-derived SAM to drive parabrachial epigenetic rewiring in pancreatic cancer.” This work uncovers a novel mechanism underlying PDAC-induced pain–depression comorbidity. PDAC upregulates METTL14 expression in glutamatergic neurons of the lateral parabrachial nucleus (LPBN^{^Glu}) in mice. Together with tumor-derived SAM, elevated METTL14 enhances m⁶A modification of adrenomedullin (ADM) and increases its expression, leading to hyperexcitability of LPBN^{^Glu} neurons and activation of the LPBN^{^Glu}→PVT^{^Glu}/LH^{^Glu} circuits, ultimately driving comorbidity. Targeted inhibition or deletion of METTL14 in LPBN^Glu neurons, or reduction of SAM levels through a methionine-restricted diet, alleviates comorbid symptoms and suppresses tumor growth.

https://doi.org/10.1016/j.neuron.2025.10.002

Severe Pain–Depression Comorbidity in PDAC Mice Is Accompanied by Elevated METTL14 Expression in Glutamatergic Neurons of the Lateral Parabrachial Nucleus (LPBN^{^Glu})

Using an orthotopic PDAC model established by intrapancreatic injection of luciferase-expressing K8484 cells (Fig. 1A–C), the study found that tumor-bearing mice exhibited persistent pain-like behaviors (Fig. 1D) and depression-like behaviors (Fig. 1E). Because comorbid phenotypes stabilized in both male and female mice at 4 weeks post-surgery, subsequent experiments focused on this time point, with male mice used as the primary subjects. c-Fos staining further identified the LPBN as the principal brain region showing tumor-induced neural activation, rather than other related regions (Fig. 1G). In this region, the m⁶A methyltransferase METTL14 showed specific and enriched upregulation at both RNA and protein levels (Fig. 1H–J), and METTL14 expression was strongly positively correlated with pain-like and depression-like behaviors in PDAC mice (Fig. 1K). Cell-type–specific analyses revealed that METTL14 was predominantly expressed in neurons (Fig. 1L) and was specifically enriched in LPBN glutamatergic neurons (Fig. 1M). These findings indicate that METTL14 in LPBN^{^Glu} neurons plays a critical role in PDAC-associated comorbidity.

Figure 1. PDAC mice exhibit severe pain–depression comorbidity, accompanied by increased METTL14 expression in LPBN^{^Glu} neurons.

METTL14 in LPBN^{^Glu} Neurons Promotes PDAC-Induced Pain–Depression Comorbidity

To determine the functional specificity of METTL14 in LPBN^Glu neurons during PDAC-induced comorbidity, Mettl14^{^flox}^/flox (Mettl14^{^f/f}) mice were generated and injected in the LPBN with AAV-CaMKIIα-Cre-DsRed to produce conditional knockout (Mettl14-cKO) mice (Fig. 2A). Cre-mediated deletion markedly reduced METTL14 expression in LPBN^{^Glu} neurons (Fig. 2B–C) and significantly alleviated PDAC-induced nociceptive hypersensitivity and depression-like behaviors (Fig. 2D–E).

Conversely, co-injection of AAV-CaMKIIα-Cre-DsRed and AAV-DIO-Mettl14-mCherry into the LPBN of wild-type mice (Fig. 2F–H) revealed that, compared with empty vector controls (AAV-DIO-mCherry), METTL14 overexpression induced abdominal mechanical hyperalgesia, increased hunching scores, prolonged immobility times in the TST and FST, and reduced sucrose preference in the SPT—hallmark behaviors of pain–depression comorbidity (Fig. 2I–J). Collectively, these results demonstrate that METTL14 in LPBN^{^Glu} neurons is essential for the initiation and progression of PDAC-induced pain–depression comorbidity.

Figure 2. METTL14 in LPBN^{^Glu} neurons promotes PDAC-induced pain–depression comorbidity.

Hyperexcitability of LPBN^{^Glu} Neurons Contributes to METTL14-Mediated Comorbidity

To investigate the mechanisms by which METTL14 in LPBN^{^Glu} neurons contributes to PDAC-induced comorbidity, RNA sequencing (RNA-seq) was performed on the LPBN from PDAC and control mice. Pathway enrichment analysis revealed PDAC-associated enrichment of pathways related to behavioral regulation and synaptic translation (Fig. 3A). In the LPBN of Mettl14-cKO mice, 2,177 differentially expressed genes were identified (Fig. 3B). Gene Ontology analysis indicated that METTL14 regulates LPBN neural activity through pathways involving cytosolic calcium dynamics, calcium transport, and pain perception within G protein–coupled receptor signaling (Fig. 3C).

Fiber photometry recordings showed that spontaneous calcium signals and calcium transients evoked by von Frey and TST stimuli were significantly enhanced in LPBN^Glu neurons of PDAC mice (Fig. 3D–G). Whole-cell patch-clamp recordings confirmed intrinsic hyperexcitability of these neurons at both spontaneous and evoked levels (Fig. 3H–K). Chemogenetic inhibition of LPBN^{^Glu} neurons by co-injecting AAV-CaMKIIα-Cre and AAV-DIO-hM4Di-mCherry into the LPBN of PDAC mice, followed by intraperitoneal CNO administration, markedly improved nociceptive hypersensitivity and depression-like behaviors and slowed tumor growth (Fig. 3L–M). These findings indicate that hyperexcitability of LPBN^{^Glu} neurons not only mediates PDAC-induced pain–depression comorbidity but also promotes peripheral tumor growth.

Figure 3. Hyperexcitability of LPBN^{^Glu} neurons participates in METTL14-mediated pain–depression comorbidity.

METTL14 in LPBN^{^Glu} Neurons Regulates Neuronal Excitability and Contributes to Pain–Depression Comorbidity

To determine whether METTL14 affects PDAC-induced comorbidity by regulating LPBN^{^Glu} neuronal excitability, PDAC mice received co-injections of AAV-CaMKIIα-GCaMP6s and AAV-CaMKIIα-shMettl14-EGFP into the LPBN (Fig. 4A). Baseline neuronal activity was recorded, followed by behavioral testing with concurrent monitoring of stimulus-evoked calcium dynamics (Fig. 4B). METTL14 knockdown significantly reduced calcium signals in LPBN^{^Glu} neurons during 0.16 g von Frey stimulation, tail suspension, and forced swim tests (Fig. 4C–D). Whole-cell patch-clamp recordings further demonstrated that loss of METTL14 reduced LPBN^Glu excitability, as evidenced by decreased action potential firing frequency, more negative resting membrane potential, and increased rheobase (Fig. 4E–H).

Conversely, co-injection of AAV-DIO-Mettl14-mCherry and AAV-CaMKIIα-GCaMP6s into the LPBN of CaMKIIα-Cre mice (Fig. S7A–B) showed that METTL14 overexpression increased neuronal excitability, particularly under behaviorally relevant stimuli (Fig. 4I–J). Subsequent chemogenetic inhibition via AAV-DIO-hM4Di-mCherry significantly alleviated METTL14 overexpression–induced pain–depression comorbidity (Fig. 4K–L). Together, these results demonstrate that METTL14 modulates LPBN^Glu neuronal excitability and plays a pivotal role in PDAC-induced pain–depression comorbidity.

Figure 4. METTL14 in LPBN^{^Glu}neurons regulates neuronal excitability and contributes to pain–depression comorbidity.

METTL14-Mediated m⁶A Modification Regulates LPBN^{^Glu}Neuron–Associated Comorbidity via ADM

To elucidate how METTL14-mediated m⁶A modification drives PDAC-induced neural adaptation, methylated RNA immunoprecipitation sequencing (MeRIP-seq) revealed widespread m⁶A modifications in the LPBN of PDAC mice, with dot blot assays confirming a significant global increase (Fig. 5A–B). Enrichment analysis showed that differentially methylated genes were associated with neurobiological processes closely linked to neuronal hyperexcitability, including synaptic organization, glutamate receptor signaling, calcium signaling pathways, and neuroactive ligand–receptor interactions (Fig. 5C).

Integrative analysis of activity-regulated genes (ARGs), differentially expressed genes, and significant MeRIP-seq peaks identified Adm as a key overlapping gene (Fig. 5D). Adm mRNA and protein levels were markedly elevated in the LPBN of PDAC mice and showed strong spatial overlap with METTL14 expression (Fig. 5E–F). Epitranscriptomic profiling revealed specific m⁶A enrichment within the CDS and 3′UTR regions of Adm mRNA in PDAC mice (Fig. 5G), with MeRIP-qPCR confirming increased methylation (Fig. 5H). Luciferase reporter assays demonstrated that METTL14 overexpression selectively enhanced the activity of reporters containing the wild-type Adm 3′UTR m⁶A sites, an effect that was significantly attenuated when these sites were mutated (Fig. 5I–J).

Functionally, local administration of the ADM receptor antagonist ADM22–52 reduced c-Fos expression in relevant neurons and reversed METTL14 overexpression–induced comorbid behaviors (Fig. 5K–M). Together, these findings delineate a critical METTL14–m⁶A–ADM axis in the LPBN that drives PDAC-induced pain–depression comorbidity.

Figure 5. In LPBN^{^Glu} neurons, METTL14-mediated m⁶A modification of ADM drives pain–depression comorbidity.

The LPBN^^Glu→PVT^{^Glu}/LH^{^Glu} Circuit Regulates PDAC-Induced Pain–Depression Comorbidity

To identify the downstream circuits of LPBN^{^Glu} neurons involved in PDAC-induced pain–depression comorbidity, AAV-CaMKIIα-mCherry was injected into the LPBN of naïve mice to specifically label these neurons (Fig. 6A). Positive axonal fibers were detected in multiple brain regions, including the paraventricular thalamus (PVT) and lateral hypothalamus (LH), with the most prominent c-Fos induction observed in the PVT and LH of PDAC mice (Fig. 6B–C).

Subsequently, an anterograde viral strategy was used by injecting AAV2/1-hSyn-Cre into the LPBN and Cre-dependent AAV-DIO-EGFP into the PVT or LH (Fig. 6D), confirming direct excitatory projections from LPBN^Glu neurons to the PVT and LH (Fig. 6E–F). To assess the functional role of these circuits, AAV2/1-CaMKIIα-Cre was bilaterally injected into the LPBN of PDAC mice, together with Cre-dependent AAV-DIO-hM4Di-EGFP injected into the PVT or LH. Systemic CNO administration to silence these projections significantly alleviated comorbid behaviors (Fig. 6G–H). Consistently, optogenetic inhibition using DIO-eNpHR-mCherry and yellow-light stimulation also effectively reduced pain- and depression-like behaviors (Fig. 6I–J).

Together, these results demonstrate that the LPBN^{^Glu}→PVT^{^Glu}/LH^{^Glu} circuit is a key mediator of PDAC-induced pain–depression comorbidity and represents a potential therapeutic target.

Figure 6. The LPBN^{^Glu}→PVT^{^Glu}/LH^{^Glu} circuit regulates PDAC-induced pain–depression comorbidity.

Dysregulated SAM Metabolism Contributes to PDAC-Induced Pain–Depression Comorbidity

SAM, the central methyl donor in one-carbon metabolism and the direct substrate for m⁶A methylation (Fig. 7A), was investigated for its involvement in PDAC progression and comorbidity. Analysis of The Cancer Genome Atlas (TCGA) cohort focusing on SAM-pathway genes revealed that high expression of adenosylhomocysteinase (AHCY) and methionine adenosyltransferase 2B (MAT2B)—two key enzymes that enhance SAM production—was associated with poor prognosis and more severe comorbidity in PDAC patients (Fig. 7B).

Clinical measurements showed that circulating SAM levels were significantly elevated in PDAC patients with NRS pain scores >0 and were positively correlated with pain intensity (Fig. 7C–D). In PDAC mice, plasma SAM levels increased with tumor growth and peaked at week 8 (Fig. 7E), and were strongly correlated with the severity of pain-like and depression-like behaviors (Fig. 7F–G). To assess the functional role of SAM, the SAM inhibitor cycloleucine was locally injected into the LPBN of PDAC mice (Fig. 7H–I), which markedly alleviated abdominal pain, hunching behavior, and depression-like behaviors (Fig. 7J–K). These results indicate that SAM is a key driver of neuro–tumor interactions, with the LPBN serving as a central hub for comorbidity.

Furthermore, PDAC mice were assigned to either a methionine-restricted diet (MRD; 0.17% methionine) or a control diet (CD; 0.86% methionine) (Fig. 7L). Four weeks of MRD intervention reduced SAM levels in tumors, plasma, and the LPBN (Fig. 7M), inhibited tumor growth without affecting body weight (Fig. 7N–O), alleviated pain after 2 weeks and depression-like behaviors after 3 weeks, with benefits persisting until week 8 (Fig. 7P–Q). These findings demonstrate that SAM metabolism contributes to PDAC-induced pain and depression, and that MRD exerts protective effects on both comorbidity and tumor progression.

Figure 7. Dysregulated S-adenosylmethionine (SAM) metabolism contributes to PDAC-induced pain–depression comorbidity.

Conclusion

This study focuses on the mechanisms underlying PDAC-induced pain–depression comorbidity and, for the first time, delineates a core “tumor–metabolite–neuron” regulatory axis. Through bidirectional neuro–tumor interactions and metabolic reprogramming, PDAC leads to a marked elevation of circulating S-adenosylmethionine (SAM) levels in both patients and mouse models. Concurrently, tumor signals upregulate METTL14 expression in LPBN^{^Glu} neurons. Together, elevated SAM and METTL14 synergistically enhance m⁶A modification of ADM mRNA and increase its expression, triggering hyperexcitability of LPBN^{^Glu}neurons and activation of the LPBN^{^Glu}→PVT^{^Glu}/LH^{^Glu} neural circuits, ultimately driving comorbidity.

Targeted inhibition of METTL14, ADM, or the identified neural circuits, as well as reduction of SAM levels through a methionine-restricted diet, simultaneously alleviates comorbid symptoms and suppresses tumor progression. Clinical data further support circulating SAM as a potential biomarker of comorbidity. Given its ease of implementation and minimal side effects, methionine-restricted dietary intervention offers a promising new therapeutic avenue for the clinical management of PDAC-induced pain–depression comorbidity.

The viral tools used in this study are available from
Brain Case Biotech（bd@ebraincase.com):

Product Categories	Number	Product Name
Fluorescent Proteins	BC-0015	rAAV-EF1α-DIO-EGFP
	BC-0016	rAAV-EF1α-DIO-mCherry
	BC-0027	rAAV-CaMKIIα-EGFP
	BC-0028	rAAV-CaMKIIα-mCherry
Recombinases	BC-0164	rAAV-CaMKIIα-Cre
	BC-0159	rAAV-hSyn-SV40NLS-Cre
	BC-1468	AAV-CaMKIIα-Cre-P2A-DsRed2
Chemogenetic	BC-0155	rAAV-EF1α-DIO-hM4D(Gi)-mCherry
Optogenetic	BC-0126	rAAV-EFα-DIO-eNpHR3.0-mCherry
Calcium Indicator	BC-0081	rAAV-CaMKIIα-GCaMP6s

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Client Article | Neuron | Prof. Jingdun Xie’s Team at Sun Yat-sen University Decodes PDAC Comorbidity: How the Tumor–Metabolism–Neuron Axis Drives Pain and Depression

Severe Pain–Depression Comorbidity in PDAC Mice Is Accompanied by Elevated METTL14 Expression in Glutamatergic Neurons of the Lateral Parabrachial Nucleus (LPBN^{^Glu})

METTL14 in LPBN^{^Glu} Neurons Promotes PDAC-Induced Pain–Depression Comorbidity

Hyperexcitability of LPBN^{^Glu} Neurons Contributes to METTL14-Mediated Comorbidity

METTL14 in LPBN^{^Glu} Neurons Regulates Neuronal Excitability and Contributes to Pain–Depression Comorbidity

METTL14-Mediated m⁶A Modification Regulates LPBN^{^Glu}Neuron–Associated Comorbidity via ADM

The LPBN^^Glu→PVT^{^Glu}/LH^{^Glu} Circuit Regulates PDAC-Induced Pain–Depression Comorbidity

Dysregulated SAM Metabolism Contributes to PDAC-Induced Pain–Depression Comorbidity

Conclusion

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Client Article | Neuron | Prof. Jingdun Xie’s Team at Sun Yat-sen University Decodes PDAC Comorbidity: How the Tumor–Metabolism–Neuron Axis Drives Pain and Depression

Severe Pain–Depression Comorbidity in PDAC Mice Is Accompanied by Elevated METTL14 Expression in Glutamatergic Neurons of the Lateral Parabrachial Nucleus (LPBN^Glu)

METTL14 in LPBN^Glu Neurons Promotes PDAC-Induced Pain–Depression Comorbidity

Hyperexcitability of LPBN^Glu Neurons Contributes to METTL14-Mediated Comorbidity

METTL14 in LPBN^Glu Neurons Regulates Neuronal Excitability and Contributes to Pain–Depression Comorbidity

METTL14-Mediated m⁶A Modification Regulates LPBN^Glu Neuron–Associated Comorbidity via ADM

The LPBN^Glu→PVT^Glu/LH^Glu Circuit Regulates PDAC-Induced Pain–Depression Comorbidity

Dysregulated SAM Metabolism Contributes to PDAC-Induced Pain–Depression Comorbidity

Conclusion

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