Adipose tissue collagen VI in obesity.
OBJECTIVE
Basic science studies show that the extracellular matrix of adipose tissue, mainly represented by collagen VI, is dysfunctional in obesity and contributes to the development of the metabolic syndrome. We hypothesized in humans that increased collagen VI alpha3-subunit (COL6A3) mRNA is associated with adipose tissue macrophage chemotaxis and inflammation and that weight gain is accompanied by changes in the expression of COL6A3.


METHODS
Adipose tissue biopsies were obtained from a cross-sectional study (n = 109), an overfeeding study (n = 9), and a pioglitazone treatment study (n = 14). Adipose tissue gene expression was measured by quantitative RT-PCR, immunohistochemistry, and adipocyte sizing by fixation with osmium and Coulter counting. Body composition was measured by dual-energy x-ray absorptiometry and visceral adipose tissue by computed tomography. Patients with high or low COL6A3 mRNA were compared by one-way ANOVA.


RESULTS
In humans, immunohistochemistry revealed that COL6 is present in adipose tissue extracellular matrix. COL6A3 mRNA is correlated with body mass index (r = 0.60, P < 0.0001) and fat mass (r = 0.41, P < 0.0001). COL6A3 expression was similar in obese vs. type 2 diabetes patients. Obese subjects with high COL6A3 mRNA had greater visceral adipose tissue mass (P < 0.05), lower size of small and medium adipocytes (P < 0.05), more CD68+ and CD163/MAC2+ macrophages, and increased macrophage inflammatory protein-1alpha and macrophage chemoattractant protein-1alpha mRNA (P < 0.05). Eight weeks of overfeeding increased body weight and COL6A3 mRNA (P < 0.05). Pioglitazone decreased COL6A3 mRNA, and the change was inversely proportional to baseline COL6A3 mRNA (r = -0.95, P < 0.0001).


CONCLUSIONS
These results are consistent with basic science data, suggesting that COL6A3 might contribute to adipose tissue inflammation.
Pasarica
Magdalena
M
Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, Louisiana 70808, USA.
Gowronska-Kozak
Barbara
B
Burk
David
D
Remedios
Isabel
I
Hymel
David
D
Gimble
Jeff
J
Ravussin
Eric
E
Bray
George A
GA
Smith
Steven R
SR
D017667:Adipocytes / Q000502:physiology / Q000648:ultrastructure; D000273:Adipose Tissue / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D015703:Antigens, CD / Q000096:biosynthesis; D015214:Antigens, Differentiation, Myelomonocytic / Q000096:biosynthesis; D001823:Body Composition / Q000235:genetics; D015992:Body Mass Index; D048429:Cell Size; D002634:Chemotaxis, Leukocyte / Q000502:physiology; D024142:Collagen Type VI / Q000096:biosynthesis* / Q000235:genetics*; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D006963:Hyperphagia / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D007150:Immunohistochemistry; D007249:Inflammation / Q000378:metabolism / Q000473:pathology; D008264:Macrophages / Q000378:metabolism; D008297:Male; D009765:Obesity / Q000378:metabolism*; D000077205:Pioglitazone; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D045162:Thiazolidinediones / Q000627:therapeutic use; D015430:Weight Gain / Q000235:genetics; D055815:Young Adult; D000097382:CD68 Molecule
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D024142:Collagen Type VI; D007004:Hypoglycemic Agents; D000077205:Pioglitazone; D012333:RNA, Messenger; D045162:Thiazolidinediones; C067980:CD68 antigen, human; D000097382:CD68 Molecule