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Loss of HIF-1α in the notochord results in cell death and complete disappearance of the nucleus pulposus.

Merceron C, Mangiavini L, Robling A, Wilson TL, Giaccia AJ, Shapiro IM, Schipani E, Risbud MV - PLoS ONE (2014)

Bottom Line: This structure is covered superior and inferior side by cartilaginous endplates (CEP).The NP is a unique tissue within the IVD as it results from the differentiation of notochordal cells, whereas, AF and CEP derive from the sclerotome.Loss of the NP in mutant mice significantly reduced the IVD biomechanical properties by decreasing its ability to absorb mechanical stress.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, Medical School, University of Michigan, Ann Arbor, Michigan, United States of America; Inserm, UMRS 791-LIOAD, Centre for Osteoarticular and Dental Tissue Engineering, Group STEP 'Skeletal Tissue Engineering and Physiopathology', Nantes, France; LUNAM, Nantes University, Faculty of Dental Surgery, Nantes, France.

ABSTRACT
The intervertebral disc (IVD) is one of the largest avascular organs in vertebrates. The nucleus pulposus (NP), a highly hydrated and proteoglycan-enriched tissue, forms the inner portion of the IVD. The NP is surrounded by a multi-lamellar fibrocartilaginous structure, the annulus fibrosus (AF). This structure is covered superior and inferior side by cartilaginous endplates (CEP). The NP is a unique tissue within the IVD as it results from the differentiation of notochordal cells, whereas, AF and CEP derive from the sclerotome. The hypoxia inducible factor-1α (HIF-1α) is expressed in NP cells but its function in NP development and homeostasis is largely unknown. We thus conditionally deleted HIF-1α in notochordal cells and investigated how loss of this transcription factor impacts NP formation and homeostasis at E15.5, birth, 1 and 4 months of age, respectively. Histological analysis, cell lineage studies, and TUNEL assay were performed. Morphologic changes of the mutant NP cells were identified as early as E15.5, followed, postnatally, by the progressive disappearance and replacement of the NP with a novel tissue that resembles fibrocartilage. Notably, lineage studies and TUNEL assay unequivocally proved that NP cells did not transdifferentiate into chondrocyte-like cells but they rather underwent massive cell death, and were completely replaced by a cell population belonging to a lineage distinct from the notochordal one. Finally, to evaluate the functional consequences of HIF-1α deletion in the NP, biomechanical testing of mutant IVD was performed. Loss of the NP in mutant mice significantly reduced the IVD biomechanical properties by decreasing its ability to absorb mechanical stress. These findings are similar to the changes usually observed during human IVD degeneration. Our study thus demonstrates that HIF-1α is essential for NP development and homeostasis, and it raises the intriguing possibility that this transcription factor could be involved in IVD degeneration in humans.

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Massive cell death in the mutant NP at birth.Tunel assay of NP at birth in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice, respectively. DAPI (a,b), TUNEL (c,d) and merged (e, f) microphotographs are presented. Bar = 200 µm.
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pone-0110768-g010: Massive cell death in the mutant NP at birth.Tunel assay of NP at birth in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice, respectively. DAPI (a,b), TUNEL (c,d) and merged (e, f) microphotographs are presented. Bar = 200 µm.

Mentions: Next, we evaluated cell death by TUNEL staining. Massive cell death (39.2±4.46%) occurred at birth in the mutant NP, whereas no positive TUNEL signal could be detected in the NP of control specimens (Figure 10 and Figure S3). Conversely, no positive TUNEL signal was present at E15.5 and postnatally in either control or mutant specimens (Figure S4).


Loss of HIF-1α in the notochord results in cell death and complete disappearance of the nucleus pulposus.

Merceron C, Mangiavini L, Robling A, Wilson TL, Giaccia AJ, Shapiro IM, Schipani E, Risbud MV - PLoS ONE (2014)

Massive cell death in the mutant NP at birth.Tunel assay of NP at birth in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice, respectively. DAPI (a,b), TUNEL (c,d) and merged (e, f) microphotographs are presented. Bar = 200 µm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4206488&req=5

pone-0110768-g010: Massive cell death in the mutant NP at birth.Tunel assay of NP at birth in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice, respectively. DAPI (a,b), TUNEL (c,d) and merged (e, f) microphotographs are presented. Bar = 200 µm.
Mentions: Next, we evaluated cell death by TUNEL staining. Massive cell death (39.2±4.46%) occurred at birth in the mutant NP, whereas no positive TUNEL signal could be detected in the NP of control specimens (Figure 10 and Figure S3). Conversely, no positive TUNEL signal was present at E15.5 and postnatally in either control or mutant specimens (Figure S4).

Bottom Line: This structure is covered superior and inferior side by cartilaginous endplates (CEP).The NP is a unique tissue within the IVD as it results from the differentiation of notochordal cells, whereas, AF and CEP derive from the sclerotome.Loss of the NP in mutant mice significantly reduced the IVD biomechanical properties by decreasing its ability to absorb mechanical stress.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, Medical School, University of Michigan, Ann Arbor, Michigan, United States of America; Inserm, UMRS 791-LIOAD, Centre for Osteoarticular and Dental Tissue Engineering, Group STEP 'Skeletal Tissue Engineering and Physiopathology', Nantes, France; LUNAM, Nantes University, Faculty of Dental Surgery, Nantes, France.

ABSTRACT
The intervertebral disc (IVD) is one of the largest avascular organs in vertebrates. The nucleus pulposus (NP), a highly hydrated and proteoglycan-enriched tissue, forms the inner portion of the IVD. The NP is surrounded by a multi-lamellar fibrocartilaginous structure, the annulus fibrosus (AF). This structure is covered superior and inferior side by cartilaginous endplates (CEP). The NP is a unique tissue within the IVD as it results from the differentiation of notochordal cells, whereas, AF and CEP derive from the sclerotome. The hypoxia inducible factor-1α (HIF-1α) is expressed in NP cells but its function in NP development and homeostasis is largely unknown. We thus conditionally deleted HIF-1α in notochordal cells and investigated how loss of this transcription factor impacts NP formation and homeostasis at E15.5, birth, 1 and 4 months of age, respectively. Histological analysis, cell lineage studies, and TUNEL assay were performed. Morphologic changes of the mutant NP cells were identified as early as E15.5, followed, postnatally, by the progressive disappearance and replacement of the NP with a novel tissue that resembles fibrocartilage. Notably, lineage studies and TUNEL assay unequivocally proved that NP cells did not transdifferentiate into chondrocyte-like cells but they rather underwent massive cell death, and were completely replaced by a cell population belonging to a lineage distinct from the notochordal one. Finally, to evaluate the functional consequences of HIF-1α deletion in the NP, biomechanical testing of mutant IVD was performed. Loss of the NP in mutant mice significantly reduced the IVD biomechanical properties by decreasing its ability to absorb mechanical stress. These findings are similar to the changes usually observed during human IVD degeneration. Our study thus demonstrates that HIF-1α is essential for NP development and homeostasis, and it raises the intriguing possibility that this transcription factor could be involved in IVD degeneration in humans.

Show MeSH
Related in: MedlinePlus