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Abstract: FR-PO392

Circadian Clock Provides Beneficial Effects Against the Endothelial Dysfunction by Regulating Porphyrins Synthesis and Heme Oxygenase-1 Expression

Session Information

  • Hypertension and CVD: Basic
    November 03, 2023 | Location: Exhibit Hall, Pennsylvania Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Hypertension and CVD

  • 1601 Hypertension and CVD: Basic


  • Negoro, Hideyuki, Harvard Medical School, Boston, United States

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. Heme oxygenase-1 (HO-1) is an intracellular enzyme which catalyzes the oxidation of heme to generate ferrous iron, carbon monoxide, and biliverdin, which is subsequently converted to bilirubin. 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 HO-1generation which play an important part in the protection of vascular diseases.


Congenic 12- to 16-week-old male, wild-type and Bmal1-KO littermate mice were generated from heterozygote breeding. 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). We also knocked down Bmal1 to evaluate the protein levels of HO-1 expression in the knocked down cells.


In aorta from Bmal1 KO mice, there was a reduction in HO-1 expression 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 to lead to increase of HO-1. HO-1 levels followed a circadian pattern, and this pattern was absent in Bmal1 KO mice.


These findings indicate that circadian clock provides beneficial effects against the endothelial dysfunction to promote atherogenesis by regulating Porphyrins synthesis and HO-1 expression. This study establishes a mechanistic connection between Bmal1 and cardiovascular phenotype.


  • Government Support – Non-U.S.