title: Circadian factors BMAL1 and RORα control HIF-1α transcriptional activity in nucleus pulposus cells: implications in maintenance of intervertebral disc health.
abstract: BMAL1 and RORα are major regulators of the circadian molecular oscillator. Since previous work in other cell types has shown cross talk between circadian rhythm genes and hypoxic signaling, we investigated the role of BMAL1 and RORα in controlling HIF-1-dependent transcriptional responses in NP cells that exist in the physiologically hypoxic intervertebral disc. HIF-1-dependent HRE reporter activity was further promoted by co-transfection with either BMAL1 or RORα. In addition, stable silencing of BMAL1 or inhibition of RORα activity resulted in decreased HRE activation. Inhibition of RORα also modulated HIF1α-TAD activity. Interestingly, immunoprecipitation studies showed no evidence of BMAL1, CLOCK or RORα binding to HIF-1α in NP cells. Noteworthy, stable silencing of BMAL1 as well as inhibition of RORα decreased expression of select HIF-1 target genes including VEGF, PFKFB3 and Eno1. To delineate if BMAL1 plays a role in maintenance of disc health, we studied the spinal phenotype of BMAL1-null mice. The lumbar discs of null mice evidenced decreased height, and several parameters associated with vertebral trabecular bone quality were also affected in nulls. In addition, null animals showed a higher ratio of cells to matrix in NP tissue and hyperplasia of the annulus fibrosus. Taken together, our results indicate that BMAL1 and RORα form a regulatory loop in the NP and control HIF-1 activity without direct interaction. Importantly, activities of these circadian rhythm molecules may play a role in the adaptation of NP cells to their unique niche.
authors.affiliation: Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, USA.|Department of Orthopaedic Surgery, Surgical Science, Tokai University School of Medicine, Isehara, Kanagawa, Japan.|Department of Anatomy and Cellular Biology, Basic Medical Science, Tokai University School of Medicine, Isehara, Kanagawa, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Suyama
authors.affiliation: Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, USA.|Program in Cell and Developmental Biology, Jefferson College of Biomedical Sciences, Thomas Jefferson University, Philadelphia, USA.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Silagi
authors.affiliation: Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, USA.|Program in Cell and Developmental Biology, Jefferson College of Biomedical Sciences, Thomas Jefferson University, Philadelphia, USA.
authors.forename: Hyowon
authors.initials: H
authors.lastname: Choi
authors.affiliation: Department of Anatomy and Cellular Biology, Basic Medical Science, Tokai University School of Medicine, Isehara, Kanagawa, Japan.
authors.forename: Kou
authors.initials: K
authors.lastname: Sakabe
authors.affiliation: Department of Orthopaedic Surgery, Surgical Science, Tokai University School of Medicine, Isehara, Kanagawa, Japan.
authors.forename: Joji
authors.initials: J
authors.lastname: Mochida
authors.affiliation: Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, USA.|Program in Cell and Developmental Biology, Jefferson College of Biomedical Sciences, Thomas Jefferson University, Philadelphia, USA.
authors.forename: Irving M
authors.initials: IM
authors.lastname: Shapiro
authors.affiliation: Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, USA.|Program in Cell and Developmental Biology, Jefferson College of Biomedical Sciences, Thomas Jefferson University, Philadelphia, USA.
authors.forename: Makarand V
authors.initials: MV
authors.lastname: Risbud
mesh_terms: D056930:ARNTL Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D002940:Circadian Rhythm; D005786:Gene Expression Regulation; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics*; D007403:Intervertebral Disc / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1 / Q000235:genetics / Q000378:metabolism*; D000070614:Nucleus Pulposus / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
chemical_list: D056930:ARNTL Transcription Factors; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1
keywords: BMAL1; HIF-1; Pathology Section; RORα; intervertebral disc; nucleus pulposus