Abstract: TH-PO0258
Circadian Clock Provides Beneficial Effects Against Endothelial Dysfunction by Regulating Porphyrin Generation and Heme Biosynthesis
Session Information
- Hypertension and CVD: Mechanisms
November 06, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Hypertension and CVD
- 1601 Hypertension and CVD: Basic
Author
- Negoro, Hideyuki, Harvard Medical School, Boston, Massachusetts, United States
Background
The circadian clock is a molecular mechanism that confers 24 hours variations in gene expression and function to regulate many physiological functions. Chronic circadian clock disruption is associated with vascular stiffness and dysfunction in endothelial signaling and responses.
Heme is a ligand of REV-ERBα and REV-ERBβ which modulate circadian rhythms by binding to the ROR region of CLOCK or BMAL1 to suppress the expression of these genes.
5-Aminolevulinic acid (ALA) is the common precursor of heme. The iron ion is inserted into Protoporphyrin IX to form heme in the mitochondria and incorporated into hemoproteins. These products have anti-inflammatory, anti-apoptotic and anti-thrombotic properties. In this study, we observed if the deletion of Bmal1, a critical component of the circadian clock, can influence porphyrins and heme synthesis which play an important part in the protection of vascular diseases.
Methods
Congenic 12- to 16-week-old male, wild-type and Bmal1-KO littermate mice were generated from heterozygote breeding to be used for these studies. We also knocked down Bmal1 to evaluate the levels of porphyrin and heme expression in the knocked down cells. To synchronize circadian rhythms, serum stimulations were performed. Cells were also pre-incubated with or without 1 mM ALA and 0.5 mM sodium ferrous citrate (SFC).
Results
In aorta from Bmal1 KO mice, there was a reduction in porphyrin and heme synthesis in mice with a dysfunctional circadian rhythm. Bmal1 KO mice display pre-mature aging to have a dramatic prothrombotic phenotype. This phenotype is linked to the regulation of key risk factors for cardiovascular disease. These include HO-1 which is significantly reduced in Bmal1 KO mice.
ALA/SFC co-incubation affected the oscillation and phase of core clock genes and led to increase of porphyrin generation and heme biosynthesis. Heme levels followed a circadian pattern, and this pattern was absent in Bmal1 KO mice.
Conclusion
These findings indicate that circadian clock provides beneficial effects against the dysfunction in endothelial signaling to promote atherogenesis by regulating porphyrin generation and heme biosynthesis. This study establishes a mechanistic connection between Bmal1 and cardiovascular phenotype.
Funding
- Government Support – Non-U.S.