Loss of PERIOD1 disrupts the cardiac transcriptome and increases fibrosis in a sex-dependent manner in Dahl Salt Sensitive rats on high salt diet

Background: Salt-sensitive (SS) hypertension (HTN) drives heart disease, the leading cause of death in the United States. Investigation of cardiac mechanisms in HTN is necessary. One crucial mechanism in cardiac function is the molecular clock, which governs circadian physiology and functions in a tissue-specific manner. PERIOD1 (PER1) is a transcription factor and part of the core clock mechanism. Loss of PER1 drives HTN in pre-clinical models, and its expression is downregulated in the hearts of patients with heart disease. Previously, we published that male Dahl SS PER1 knockout (KO) rats on a high salt (HS) diet develop more severe SS HTN compared to control Dahl SS. This was associated with a disrupted circadian rhythm of heart rate. However, the mechanisms underlying cardiac dysfunction in male PER1 KO rats are unknown. Furthermore, sex differences in the loss of PER1 have not been characterized. Hypothesis: We performed unbiased hypothesis-generating transcriptomics on heart samples from male and female PER1 KO and Dahl SS rats. We hypothesized that genes associated with cardiac pathology would be preferentially upregulated in male, but not female, PER1 KO rats compared to controls, and that these transcriptomic changes would correspond to sex-dependent differences in cardiac fibrosis. Methods: Hearts were collected from male and female PER1 KO and Dahl SS rats (N=5-6) at 2 AM (active phase) after 3 weeks of a HS (4% NaCl) diet. Differentially expressed genes (DEGs) were identified through bulk RNA sequencing (Novogene). DEGs were analyzed using Qiagen Ingenuity Pathway Analysis (IPA) to determine upstream regulators and a mechanistic network. A separate cohort was used for histology. Hearts were collected at 2 PM (inactive phase) from male and female PER1 KO and Dahl SS rats. This collection timepoint is different from the previous cohort because we only needed to assess end-organ damage in this study. Cardiac fibrosis was assessed using picrosirius red staining and statistics for fibrosis were performed using two-way ANOVA. Results: For male KO vs SS comparisons, 1950 significant DEGs were identified. For male KO vs female KO, 1209 significant DEGs were identified; female KO vs SS comparisons revealed 1108 significant DEGs. IPA identified Angiotensinogen (Agt) as an upstream regulator of DEGs in male KO vs SS rats, likely acting through genes such as Tgfb1, Angpt2, and p38 Mapk (p=1.99E-32). In male KO vs female KO rats, the upstream regulator of DEGs was Agt, and its mechanistic network included Hgf, and Tgf beta (family). In female KO vs SS, Il1b was identified as an upstream regulator acting through p38 Mapk, Ifng, and Tnf (p=3.81E-13). Loss of PER1 was associated with significantly higher cardiac fibrosis in male (p=0.0026) but not female rats (p=0.4291) in post-hoc analysis. Two-way ANOVA revealed significant effects of genotype (p=0.0064) and sex (p=0.0139), with a trend towards interaction (p=0.0521). Conclusions: Loss of PER1 is associated with sex-dependent dysregulation of the cardiac transcriptome. Genes upregulated in male PER1 KO rats are associated with increased inflammation and fibrosis when compared to male SS or female PER1 KO rats. These transcriptional findings are consistent with our assessment of fibrosis, demonstrating that male PER1 KO rats indeed have significantly higher fibrosis than male SS or female KOs. It is possible that targeting the pathways identified by IPA could attenuate pathology associated with loss of PER1 in SS HTN. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.