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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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Progressive disappearance of the mutant NP postnatally.A. H&E staining of NB (a,b), 1 month (c,d) and 4 months (e,f) NP in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice. Bar = 50 µm. B. Safranin O staining of 1 month (a,b) NP in control (HIF-1αf/f) (a) and mutant (Foxa2iCre;HIF-1αf/f) (b) mice. Bar = 100 µm.
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pone-0110768-g004: Progressive disappearance of the mutant NP postnatally.A. H&E staining of NB (a,b), 1 month (c,d) and 4 months (e,f) NP in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice. Bar = 50 µm. B. Safranin O staining of 1 month (a,b) NP in control (HIF-1αf/f) (a) and mutant (Foxa2iCre;HIF-1αf/f) (b) mice. Bar = 100 µm.

Mentions: The mutant NP phenotype was more severe at birth (Figure 4A a-b), and by 1 month the NP had virtually disappeared in mutant mice (Figure 4A c-f). In addition, the space previously occupied by the NP was now filled by a fibrocartilaginous tissue that strongly stained for Safranin O (Figure 4B), thus resembling the inner layer of AF. Interestingly, whole mount Alizarin Red S/Alcian Blue staining performed at birth (Figure S2A) and H&E staining of specimens collected between E15.5 and 4 months of age (Figure S2B) did not reveal any obvious abnormality in either mutant VB, AF or CEP, when compared to controls.


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)

Progressive disappearance of the mutant NP postnatally.A. H&E staining of NB (a,b), 1 month (c,d) and 4 months (e,f) NP in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice. Bar = 50 µm. B. Safranin O staining of 1 month (a,b) NP in control (HIF-1αf/f) (a) and mutant (Foxa2iCre;HIF-1αf/f) (b) mice. Bar = 100 µm.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0110768-g004: Progressive disappearance of the mutant NP postnatally.A. H&E staining of NB (a,b), 1 month (c,d) and 4 months (e,f) NP in control (Foxa2iCre;HIF-1αf/+) (a,c,e) and mutant (Foxa2iCre;HIF-1αf/f) (b,d,f) mice. Bar = 50 µm. B. Safranin O staining of 1 month (a,b) NP in control (HIF-1αf/f) (a) and mutant (Foxa2iCre;HIF-1αf/f) (b) mice. Bar = 100 µm.
Mentions: The mutant NP phenotype was more severe at birth (Figure 4A a-b), and by 1 month the NP had virtually disappeared in mutant mice (Figure 4A c-f). In addition, the space previously occupied by the NP was now filled by a fibrocartilaginous tissue that strongly stained for Safranin O (Figure 4B), thus resembling the inner layer of AF. Interestingly, whole mount Alizarin Red S/Alcian Blue staining performed at birth (Figure S2A) and H&E staining of specimens collected between E15.5 and 4 months of age (Figure S2B) did not reveal any obvious abnormality in either mutant VB, AF or CEP, when compared to controls.

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