ADAM12 induces actin cytoskeleton and extracellular matrix reorganization during early adipocyte differentiation by regulating β integrin function
Differentiation process changes the morphology of cells. ADAMS 12, a disintegrin and metalloprotease, affects the cell morphology in preadipocytes, changing them from flattened, fibroblastic shape to a more rounded shape. Temporal regulation of multiple and interacting signaling events characterize adipogenesis, leading to the expression of adipocyte-specific genes. A cascade of transcription factors is induced that involved the sequential activation of te CCAAT/enhancer-binding proteins and the peroxisome proliferator activated receptor , leading to the activation of several genes, such as those responsible for lipid transport and metabolism. Initially, fibroblastic preadipocytes stop diving and acquire a rounded morphology. The highest levels of ADAM12 mRNA were detected in preadipocytes at the onset of differentiation. This article explains the molecular mechanism of the effects of ADAM12 on adipocyte differentiation using Transient transfections, Nothern blot analysis, Flow cytometry, Triton X-100 extraction, Protein extraction, iRNA and Microinjection et cetera. The author hypothesized that ADAM12 itself could be part of a β1 integrin cell-adhesion complex and that this might influence the adipogenic differentiation pathway.
Using the immunostaining method, it is found that ADAM12 was transiently expressed at the cell surface consequently with the reduced activity of β1. According to the Co-immunoprecipitation studies, ADAM12/β1 integrin complexes were formed in preadipocytes. From the retroviral transduction method, overexpression of ADAM12 at the surface of 3T3-L1 preadipocytes led to the degradation of actin stress fibers and formation of cortical network beneath the cell membrane. ADAM12-expressing cells were more prone to apoptosis, which could be prevented by treating the cells with β1 activating antibodies. These results show that surface expression of ADAM12 impairs the function of β1 integrins and consequently alter the organization of extracellular matrix and cytoskeleton. In conclusion, ADAM12 induces reorganization of the actin cytoskeleton, reduced cell adhesion, changes in cell survival pathways and reorganization of the fibronectin-rich ECM in fibroblastic preadipocytes. ADAM12 at the cell surface mediates its effects via a direct or indirect interaction with β1 integrin that results in an impairment of β1integrin function.
... enough nutrients into the cell. Single celled organisms have a large surface area to volume ratio because they are ... the nearest mm. Discussion It is important that cells have a large surface area to volume ratio so that they can get ... will go up. Appendices (2002) Biology: The Surface Area to Volume Ratio of a Cell [Web document] //www.geocities.com/CapeCanaveral ...
From the article “ADAM12 induces actin cytoskeleton and extracellular matrix reorganization during early adipocyte differentiation by regulating β integrin function”, the author explains the process by which ADAM12 reorganises cytoskeleton and extracellular matrix at the onset of differentiation by regulating β1 integrin function. The author had performed a previous study regarding increased adipogenesis in transgenic mice overexpressing ADAM12.
The author has done a good research on the process of Adipogenesis and types of ADAM12. He used a good number of methods to support his study.ADAM12 expression was quantified at different stages of adipocyte development. The author used t-test for statistical analysis. He used only one method for statistical analysis instead of using two or more tests like F-test, ANOVA.
In the results section ’Expression of ADAM12 in adipose tissue and during in vitro Adipogenesis’, it is given that ADAM12 was detected by immunostaining in normal mouse white and brown adipose tissue, but ADAM12 was not detected in normal human adipose tissue. So, there is no evidence that ADAM12 induces cytoskeleton and extracellular matrix reorganization in normal human tissues.
... P 140. ). The structural elements of all connective tissues are extracellular matrix (nonliving material that separates the living cells in connective ... tissue consisting of ground substance and fibers) and ... of cells which unite together to form contrary tissues. Tissues are a group of similar cells and their ...
In the results section ‘Formation of ADAM12/β1 integrin complexes and reduced β1 integrin activity as assessed by 12G10 immunostaining upon ADAM12 cell-surface localizatin’, using the immunostaining method, there was little or no detectable difference in the total amount of β1 integrin as determined by immunostainin in K20 antibody. These results indicate that upon ADAM12 cell-surface expression, β1 integrin/ADAM complexed are formed, which appears to result in reduced β1 integrin activity.
RT-PCR showed that ADAM9, 10, 17 and 19 are also expressed in the 3T3-L1 cells during Adipogenesis. The finding that ADAM12 null mice do not exhibit striking defects in the white adipose tissue further suggests function overlap among the ADAMs.Therefore, other members of ADAMs family may be responsible for reorganization of cytoskeleton and extracellular matrix. The author should have done a research to evaluate the contribution by other members of ADAMs family.
The localization of ADAM12 and b1 integrin in the cell membrane has not yet been determined. Research is to be done on the physiological substrate for the ADAM12 protease. The recombinant cysteine-rich domain of ADAM12 intereacts with syndecans and mediates integrin-dependent cell spreading.
I conclude that the author has done a good research on the role of ADAM12 in the cytoskeleton and extracellular matrix reorganization, but he did not present the quantification of impairment of β1 integrin.