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Abstract: PO1830

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

Session Information

Category: Hypertension and CVD

  • 1403 Hypertension and CVD: Mechanisms


  • 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 number of physiological functions in humans. Chronic circadian clock disruption is associated with vascular stiffness and dysfunction in endothelial signaling and responses.
5-Aminolevulinic acid (ALA) is the common precursor of heme. The iron ion is inserted into PpIX to form heme in the mitochondria and incorporated into hemoproteins. 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.
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 HO-1 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 breedings to be used for these studies. We also knocked down Bmal1 to evaluate the protein levels of HO-1 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).


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 and led 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 Heme synthesis and HO-1 expression. This study establishes a mechanistic connection between Bmal1 and cardiovascular phenotype.


  • Government Support – Non-U.S.