Biology subjects

Stumpf, I. G.

Publications and source records attributed to Stumpf, I. G..

3 recordsLinked to original sources

bioRxiv2026

The circadian clock regulates KCNH2 (hERG) promoter activity through daily temperature rhythms.

Background: KCNH2 encodes Kv11.1 channel proteins that conduct the rapidly activating delayed-rectifier K+ current (IKr), which is critical for cardiac repolarization. KCNH2 encodes two functional isoforms, Kv11.1a and Kv11.1b, via alternative transcription start sites. Kv11.1a is the principal determinant of cardiac IKr and ventricular repolarization. The circadian clock, a transcriptional-translational feedback loop that cycles with a period of ~24 hours and drives the circadian expression of many genes, including Kcnh2 in the mouse heart. Because daily body temperature rhythms provide a systemic signal that synchronizes cardiac circadian clocks, we tested whether physiological temperature cycles drive the circadian promoter activity of the cloned human KCNH2 (hKCNH2) promoter. Hypothesis: hKCNH2 is a direct transcriptional target of the circadian clock, with temperature driving its promoter activity through BMAL1:CLOCK acting at a conserved tandem E-box. Methods: We cloned the conserved proximal promoter of KCNH2 (-1631 bp upstream of Kv11.1a exon 1) to generate hKCNH2 promoter luciferase reporter constructs. Constructs were transfected into C2C12 myotubes and synchronized by serum shock (static 37{degrees}C) or temperature cycling (36.5-38.5{degrees}C). Bioluminescence was recorded and assessed for period, phase, and amplitude. BMAL1:CLOCK dependence was tested via dominant-negative CLOCK{Delta}19 co-expression. Results: Temperature cycling did not exhibit the rapid damping characteristic of serum-shock-synchronized oscillations, consistent with continuous entrainment by an external zeitgeber rather than a free-running oscillator. Deletion analysis identified a conserved tandem E-box required for oscillation under both serum shock and temperature cycling, and for BMAL1:CLOCK-dependent transactivation (1.75 {+/-} 0.21 vs. 0.86 {+/-} 0.06 RLU, p = 0.0038). CLOCK{Delta}19 reduced hKCNH2 promoter amplitude under temperature cycling without altering period. Conclusion: The circadian clock regulates KCNH2 promoter activity through daily temperature rhythms.

cell biology↗

bioRxiv2026

Housing Mice in Thermoneutrality Causes Tissue-specific Changes in Number, Identity, and Phase of Circadian-expressed mRNA Transcripts

Most laboratory mice are housed at room temperature (20-25{degrees}C), which exposes them to chronic mild cold stress because it is below their thermoneutral temperature (30{degrees}C). We hypothesized that mild cold stress suppresses circadian gene expression in peripheral tissues. We performed RNA sequencing on hearts, livers, and diaphragms collected every 4 hours over 48 hours in constant darkness from male mice to identify transcripts with approximately 24-hour rhythms. Thermoneutral housing produced tissue-specific changes in the number, identity, and timing of rhythmic transcripts without altering the expression of core circadian clock genes. In the heart, the number of rhythmic transcripts increased fourfold, whereas the diaphragm showed a 1.5-fold increase. In the liver, the overall number of rhythmic transcripts showed little change, but their identity changed by 30%. Gene Ontology analysis revealed coordinated changes in the temporal organization of metabolic pathways in the heart and liver. Together, these findings demonstrate that ambient housing temperature is a major determinant of tissue-specific circadian gene expression, altering the abundance, identity, and timing of rhythmic transcripts independently of the core circadian clock. SignificanceScientists typically house laboratory mice at room temperature, below their thermoneutrality, forcing them to increase their metabolic rate to maintain core body temperature. Since ambient temperature plays an important role in metabolism, cold stress could disrupt circadian gene expression. Comparing mice housed at room temperature with a warmer, thermoneutral temperature, we found that housing temperature causes tissue-specific differences in rhythmically expressed genes in the heart, liver, and diaphragm, without altering core clock genes. The heart was especially sensitive, with rhythmic genes peaking at the transition between subjective light and dark cycles, increasing fourfold. These results identify ambient housing temperature as an underrecognized variable that biases circadian gene expression in cardio-metabolic tissues, affecting interpretation of preclinical studies of metabolism and disease.

physiology↗

bioRxiv2024

New role of cardiomyocyte Bmal1 in the regulation of sex-specific heart transcriptomes

It has been well established that cardiovascular diseases exhibit significant differences between sexes in both preclinical models and humans. In addition, there is growing recognition that disrupted circadian rhythms can contribute to the onset and progression of cardiovascular diseases. However little is known about sex differences between the cardiac circadian clock and circadian transcriptomes in mice. Here, we show that the the core clock genes are expressed in common in both sexes but the circadian transcriptome of the mouse heart is very sex-specific. Hearts from female mice expressed significantly more rhythmically expressed genes (REGs) than male hearts and the temporal pattern of REGs was distinctly different between sexes. We next used a cardiomyocyte-specific knock out of the core clock gene, Bmal1, to investigate its role in sex-specific gene expression in the heart. All sex differences in the circadian transcriptomes were significantly diminished with cardiomyocyte-specific loss of Bmal1. Surprisingly, loss of cardiomyocyte Bmal1 also resulted in a roughly 8-fold reduction in the number of all the differentially expressed genes between male and female hearts. We conclude that cardiomyocyte-specific Bmal1, and potentially the core clock mechanism, is vital in conferring sex-specific gene expression in the adult mouse heart.

physiology↗