Every mammalian cell contains a molecular clock built from interlocking transcription-translation feedback loops. Core activators such as BMAL1 and CLOCK drive the rhythmic expression of thousands of genes, which in turn coordinate time-of-day-dependent processes including glucose handling, lipid oxidation, protein quality control and immune surveillance. When these clocks falter, the consequences are well documented: inflammation, impaired glucose homeostasis and distorted lipid metabolism, all of which are hallmark features of cancer cachexia. Previous work has shown that tumours can remotely rewire circadian programs in the liver, and the Florida group had already demonstrated that pancreatic cancer disrupts circadian gene expression in a limb muscle, the tibialis anterior. What remained unknown was whether the cardiorespiratory muscles, whose wasting is thought to be a key driver of cachexia-related morbidity and mortality, suffer the same fate.

To find out, the researchers used an orthotopic model of pancreatic ductal adenocarcinoma in which aggressive KPC tumour cells are injected directly into the pancreas of mice. Twelve days after inoculation, a time point corresponding precisely to the onset of cachexia, they collected diaphragm and heart tissue every four hours across a full twenty-four-hour cycle in constant darkness, ensuring that any rhythms they detected reflected endogenous clocks rather than external light cues. They then performed bulk RNA sequencing on each sample and applied sophisticated statistical models that treat gene expression as a continuous sinusoidal function over the day, allowing them to identify rhythmically expressed genes and to detect changes in amplitude, phase and basal expression. The design was powered at over ninety-seven percent to detect circadian rhythmicity, lending confidence to the results.

The findings were striking. In healthy mice, the diaphragm showed robust rhythmicity in 308 genes, but in tumour-bearing mice sixty-four percent of those genes lost their daily oscillations entirely. At the same time, 718 genes that were never rhythmic in healthy diaphragm gained rhythmicity in the cancer state, a wholesale remodelling of the tissue’s temporal architecture. Among the genes losing their rhythm were Nrf1, which guards mitochondrial homeostasis; Pik3c3, a key mediator of autophagy; and Fgf1, a positive modulator of glucose disposal. Genes that gained rhythmicity included inflammatory players such as Tlr7, Il18 and Il18r1, alongside troubling time-of-day-dependent losses in Glut4, the major insulin-regulated glucose transporter, and in Tfeb and Psme4, master regulators of the autophagy-lysosome system and proteasomal quality control.

The heart told a partially different story. Of 1274 genes rhythmic in healthy hearts, fifty-six percent lost their oscillations in tumour-bearing animals, while 246 genes gained rhythmicity. Crucially, core clock gene rhythmicity was largely preserved in the heart, with only Per1 showing elevated basal expression, whereas the diaphragm exhibited significant repression of core clock components including Bmal1 itself, the gene whose deletion in muscle is known to cause metabolic reprogramming, weakness and atrophy. Only about ten percent of the rhythmic genes disrupted in the cancerous hearts overlapped with those altered by cardiomyocyte-specific Bmal1 deletion, suggesting that factors extrinsic to the cardiac clock, such as systemic inflammatory or autonomic signals, are driving much of the disruption.

The temporal coordination of biological processes also collapsed in a tissue-specific manner. In healthy diaphragms, peak expression times of rhythmic genes are spread evenly across the day, reflecting a smooth distribution of daily functions. In cachectic diaphragms, that even distribution vanished, with peak expression re-clustering around the transitions between rest and activity. Genes governing lipid metabolism and amino acid sensing, which normally peak during rest and activity respectively, no longer fired at their proper times. Instead, inflammatory genes and components of ubiquitin-dependent protein breakdown dominated those windows, implying that the muscle’s daily schedule had been hijacked to prioritize immune activation and protein catabolism over metabolic maintenance.

In the heart, the overall distribution of peak expression remained even, but the content of the schedule changed. Genes that regulate heart rate, including Hcn4 and Pde4d, normally peak during the active phase to support the diurnal rise in heart rate and cardiac output driven by sympathetic tone. In tumour-bearing mice, this temporal upregulation was lost, and inflammatory genes such as Il33 and Edn1 peaked during the active phase instead. Phase-stratified analysis revealed that genes involved in adrenergic signalling and contractility, including the beta-1 adrenergic receptor Adrb1, the SERCA2 calcium pump encoded by Atp2a2, and the fatty acid oxidation regulator Ppara, were downregulated in a time-of-day-dependent fashion, while platelet activation genes rose specifically during the active phase, echoing processes implicated in cancer-associated thromboinflammation.

Perhaps the most clinically provocative discovery came from a time-course analysis spanning the entire cachexia trajectory. Drawing on a published RNA-sequencing dataset from diaphragms collected before cachexia, during mild-to-moderate disease and at severe endpoint, the team found that Bmal1 and Clock were significantly repressed by day eight after tumour inoculation, days before any measurable loss of body or muscle mass, and remained suppressed thereafter. The secondary-loop genes Rora and Nr1d1, which encode RORα and REV-ERBα, were also repressed early. Both factors have clock-independent roles in muscle: REV-ERBα promotes mitochondrial biogenesis, represses atrophy genes and is essential for muscle mass maintenance, while RORα regulates lipid homeostasis and protects against pathological fat accumulation. Their early suppression, combined with the fact that both normally restrain NF-κB inflammatory signalling, suggests that clock disruption may precede and actively contribute to diaphragm wasting rather than merely accompanying it.

Why the diaphragm is hit hardest remains an open question, but the authors point to its anatomical proximity to the pancreas, which may expose it to a concentrated bath of tumour-derived factors and a heightened inflammatory microenvironment. Previous work from the same group documented pronounced immune cell infiltration in the diaphragm before cachexia onset, and NF-κB signalling is known to suppress core clock gene expression and interfere with CLOCK:BMAL1 activity. The researchers caution that their study has limitations, including the absence of phenotypic measurements on the same animals used for circadian sequencing and uncertainty about whether the milder cardiac disruption reflects a distinct pathology or simply an earlier stage of a shared trajectory.

The therapeutic implications are considerable. Because the transcriptional damage in these muscles is time-of-day dependent, the findings support testing chronotherapy-based interventions timed to protect muscle mass and function, and they reinforce growing evidence that restoring circadian machinery can halt wasting. Recent work has shown that re-establishing hepatic circadian function in tumour-bearing mice through REV-ERBα overexpression is sufficient to spare both limb muscles and the heart from atrophy, pointing to circadian programs as master regulators of tissue cross-talk during cancer. If similar strategies can be developed for the diaphragm and heart, they could offer a fundamentally new way to defend the muscles that pancreatic cancer patients can least afford to lose.

Subject of Research: Circadian clock disruption in cardiorespiratory muscles during pancreatic cancer cachexia

Article Title: Pancreatic Cancer Disrupts Circadian Patterns of Gene Expression in Cardiorespiratory Muscles

Article References: Ducharme, J. B., Schonk, M. M., Gutierrez‐Monreal, M. A., Ferreira, L. F., Esser, K. A., Judge, A. R., & Judge, S. M. (2026). Pancreatic Cancer Disrupts Circadian Patterns of Gene Expression in Cardiorespiratory Muscles. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70383. https://doi.org/10.1002/jcsm.70383

Image Credits: AI Generated

DOI: 10.1002/jcsm.70383

Keywords: pancreatic cancer, cachexia, circadian clock, diaphragm, heart, gene expression, Bmal1, inflammation, muscle wasting, RNA sequencing, metabolism, chronotherapy