Influence of low glucose supply on the regulation of gene expression by nucleus pulposus cells and their responsiveness to mechanical loading.
OBJECTIVE
Environmental alterations resulting in a decrease in the nutrient supply have been associated with intervertebral disc (IVD) degeneration, particularly of the nucleus pulposus (NP). The goal of the present study was to examine the hypothesis that glucose deprivation alters the metabolism of NP cells and their responsiveness to mechanical loading. A possible interaction of glucose supply and hydrostatic pressure (HP) with gene expression by NP cells has not been investigated.


METHODS
The influence of glucose supply (physiological concentration: 5 mM, reduction: 0 or 0.5 mM) and cyclic HP loading (2.5 MPa, 0.1 Hz, 30 minutes) on bovine and human NP cell matrix turnover was analyzed by quantitative real-time reverse transcriptase–polymerase chain reaction. Glucose-dependent effects on cell viability were determined by trypan blue exclusion. A glycosaminoglycan (GAG) assay was performed to determine nutritional effects on the protein level.


RESULTS
Glucose reduction resulted in significant downregulations (p < 0.05) of aggrecan, collagen-I, and collagen-II gene expression by bovine NP cells. Exemplary human donors also displayed a similar trend for aggrecan and collagen-II, whereas matrix metalloproteinases (MMPs) tended to be upregulated under glucose deprivation. After HP loading, human NP cells showed individual upregulations of collagen-I and collagen-II expression, while MMP expression tended to be downregulated under glucose reduction relative to a normal glucose supply. Cell viability decreased with glucose deprivation. The GAG content was similar in all groups at Day 1, whereas at Day 3 there was a significant increase under physiological conditions.


CONCLUSIONS
Glucose deprivation strongly affected NP cell metabolism. The effects of an altered glucose supply on gene expression were more pronounced than the mechanically induced effects. Data in this study demonstrate that the glucose environment is more critical for disc cell metabolism than mechanical loads. In individual human donors, however, adequate mechanical stimuli might have a beneficial effect on matrix turnover during IVD degeneration.
Rinkler
Christina
C
Institute of Orthopaedic Research and Biomechanics, Centre for Musculoskeletal Research, University of Ulm, Ulm, Germany.
Heuer
Frank
F
Pedro
Maria Teresa
MT
Mauer
Uwe Max
UM
Ignatius
Anita
A
Neidlinger-Wilke
Cornelia
C
D000328:Adult; D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002470:Cell Survival; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D003199:Computer Systems; D015536:Down-Regulation; D005260:Female; D015870:Gene Expression; D005947:Glucose / Q000172:deficiency*; D006025:Glycosaminoglycans / Q000032:analysis; D006801:Humans; D006874:Hydrostatic Pressure; D007403:Intervertebral Disc / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D008297:Male; D020782:Matrix Metalloproteinases / Q000378:metabolism; D008875:Middle Aged; D012313:RNA / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation; D055815:Young Adult
D053674:Aggrecans; D006025:Glycosaminoglycans; D012313:RNA; D003094:Collagen; D020782:Matrix Metalloproteinases; D005947:Glucose