Laminin α4 Deficient Mice Exhibit Decreased Capacity for Adipose Tissue Expansion and Weight Gain

Obesity is a global epidemic that contributes to the increasing medical burdens related to type 2 diabetes, cardiovascular disease and cancer. A better understanding of the mechanisms regulating adipose tissue expansion could lead to therapeutics that eliminate or reduce obesity-associated morbidity and mortality. The extracellular matrix (ECM) has been shown to regulate the development and function of numerous tissues and organs. However, there is little understanding of its function in adipose tissue. In this manuscript we describe the role of laminin α4, a specialized ECM protein surrounding adipocytes, on weight gain and adipose tissue function. Adipose tissue accumulation, lipogenesis, and structure were examined in mice with a null mutation of the laminin α4 gene (Lama4−/−) and compared to wild-type (Lama4+/+) control animals. Lama4−/− mice exhibited reduced weight gain in response to both age and high fat diet. Interestingly, the mice had decreased adipose tissue mass and altered lipogenesis in a depot-specific manner. In particular, epididymal adipose tissue mass was specifically decreased in knock-out mice, and there was also a defect in lipogenesis in this depot as well. In contrast, no such differences were observed in subcutaneous adipose tissue at 14 weeks. The results suggest that laminin α4 influences adipose tissue structure and function in a depot-specific manner. Alterations in laminin composition offers insight into the roll the ECM potentially plays in modulating cellular behavior in adipose tissue expansion.</p

Laminin α4 Deficient Mice Exhibit Decreased Capacity for Adipose Tissue Expansion and Weight Gain

Obesity is a global epidemic that contributes to the increasing medical burdens related to type 2 diabetes, cardiovascular disease and cancer. A better understanding of the mechanisms regulating adipose tissue expansion could lead to therapeutics that eliminate or reduce obesity-associated morbidity and mortality. The extracellular matrix (ECM) has been shown to regulate the development and function of numerous tissues and organs. However, there is little understanding of its function in adipose tissue. In this manuscript we describe the role of laminin α4, a specialized ECM protein surrounding adipocytes, on weight gain and adipose tissue function. Adipose tissue accumulation, lipogenesis, and structure were examined in mice with a null mutation of the laminin α4 gene (Lama4-/-) and compared to wild-type (Lama4+/+) control animals. Lama4-/- mice exhibited reduced weight gain in response to both age and high fat diet. Interestingly, the mice had decreased adipose tissue mass and altered lipogenesis in a depot-specific manner. In particular, epididymal adipose tissue mass was specifically decreased in knock-out mice, and there was also a defect in lipogenesis in this depot as well. In contrast, no such differences were observed in subcutaneous adipose tissue at 14 weeks. The results suggest that laminin α4 influences adipose tissue structure and function in a depot-specific manner. Alterations in laminin composition offers insight into the roll the ECM potentially plays in modulating cellular behavior in adipose tissue expansion

The weight difference of 16 male <i>Lama4^−/−</i> mice and 12 wild-type controls were statistically significantly (p = 0.002).

<p>(A). When fed a high-fat diet (B), 8 male wild-type control mice gained statistically significant (p<0.001) more weight than the 8 <i>Lama4^−/−</i> mice. The weekly intake of standard food (C) and high fat diet (D) related to the weight of the animals were not significantly different.</p

Lipogenesis levels in adipocytes from epididymal (A) and subcutaneous (B) adipose tissue in age matched <i>Lama4^−/−</i> and <i>Lama4^+/+</i>mice.

<p>Epididymal fat pad basal lipogenesis is statistically significant between <i>Lama4^−/−</i> and <i>Lama4^+/+</i>mice (p<0.05). Subcutaneous fat pad in <i>Lama4^+/+</i>mice had statistically significant increase in lipogenesis between basal and insulin stimulated (p<0.05). The epididymal and subcutaneous n = 4. Error bars represent standard error.</p

Immunostaining of WAT.

<p>The capillaries and BMs of adipocytes of wild-type control and <i>Lama4Lama4^−/−</i> mice were positive with antibodies against laminin α2 (A, B). Laminin α4 antibodies stained both adipocytic BMs and capillaries in wild-type controls (C), while no staining was seen in mutants (D). The laminin α5 antibody (E, F) stained capillaries in <i>Lama4^−/−</i> and wild-type controls, but not the adipocytic BM. Antibodies against type IV collagen (G; H), nidogen (I, J) and perlecan (K, L) all stained both capillaries and adipocytic BMs. Laminin α1 staining was completely negative (not shown). Arrows indicate a few locations where the adipocytic BM of the <i>Lama4^−/−</i> mice appeared slightly thickened. Bar 100 µm.</p

Adipocyte diameter in subcutaneous and epididymal adipose tissue depots for age matched <i>Lama4^−/−</i> and <i>Lama4^+/+</i>mice (A).

<p>For epididymal n = 4 and subcutaneous n = 5, standard error shown as the error bars. There is a statistical difference between epididymal and subcutaneous (P<0.05). Histology images of epididymal and subcutaneous <i>Lama4^−/−</i> and <i>Lama4^+/+</i>, scale bar equals 300 µm (B). Adipocyte cell density in subcutaneous and epididymal adipose tissue depots for age matched <i>Lama4^−/−</i> and <i>Lama4^+/+</i>mice (C). For epididymal n = 4 and subcutaneous n = 5, standard error shown as error bars.</p

The <i>Lama4</i>^−/− mice had reduced fat depots.

<p>The epididymal fat is delineated in an opened 40 week old male wild-type control mice (A) and a male <i>Lama4</i>^−/− mice is shown in (B). Normalized fat pad depot mass as a % of total animal mass (C). Epididymal fat pad mass in <i>Lama4^−/−</i> mice was significantly lower than <i>Lama4^+/+</i> mice (p<0.05). Age matched animal <i>Lama4^−/−</i> and <i>Lama4^+/+</i>, n = 4 for epididymal and subcutaneous. Error bars represent standard error.</p