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Articles by R. H Amin
Total Records ( 2 ) for R. H Amin
  R. H Amin , S. T Mathews , H. S Camp , L Ding and T. Leff

The nuclear receptor peroxisome proliferator-activated receptor (PPAR) plays a key role in regulating whole body glucose homeostasis and insulin sensitivity. Although it is expressed most highly in adipose, it is also present at lower levels in many tissues, including skeletal muscle. The role muscle PPAR plays in metabolic regulation and in mediating the antidiabetic effects of the thiazolidinediones is not understood. The goal of this work was to examine the molecular and physiological effects of PPAR activation in muscle cells. We found that pharmacological activation of PPAR in primary cultured myocytes, and genetic activation of muscle PPAR in muscle tissue of transgenic mice, induced the production of adiponectin directly from muscle cells. This muscle-produced adiponectin was functional and capable of stimulating adiponectin signaling in myocytes. In addition, elevated skeletal muscle PPAR activity in transgenic mice provided a significant protection from high-fat diet-induced insulin resistance and associated changes in muscle phenotype, including reduced myocyte lipid content and an increase in the proportion of oxidative muscle fiber types. Our findings demonstrate that PPAR activation in skeletal muscle can have a significant protective effect on whole body glucose homeostasis and insulin resistance and that myocytes can produce and secrete functional adiponectin in a PPAR-dependent manner. We propose that activation of PPAR in myocytes induces a local production of adiponectin that acts on muscle tissue to improve insulin sensitivity.

  E. J Cadera , F Wan , R. H Amin , H Nolla , M. J Lenardo and M. S. Schlissel

Because of the extreme diversity in immunoglobulin genes, tolerance mechanisms are necessary to ensure that B cells do not respond to self-antigens. One such tolerance mechanism is called receptor editing. If the B cell receptor (BCR) on an immature B cell recognizes self-antigen, it is down-regulated from the cell surface, and light chain gene rearrangement continues in an attempt to edit the autoreactive specificity. Analysis of a heterozygous mutant mouse in which the NF-B–dependent IB gene was replaced with a lacZ (β-gal) reporter complementary DNA (cDNA; IB+/lacZ) suggests a potential role for NF-B in receptor editing. Sorted β-gal+ pre–B cells showed increased levels of various markers of receptor editing. In IB+/lacZ reporter mice expressing either innocuous or self-specific knocked in BCRs, β-gal was preferentially expressed in pre–B cells from the mice with self-specific BCRs. Retroviral-mediated expression of a cDNA encoding an IB superrepressor in primary bone marrow cultures resulted in diminished germline and rearranged transcripts but similar levels of RAG expression as compared with controls. We found that IRF4 transcripts were up-regulated in β-gal+ pre–B cells. Because IRF4 is a target of NF-B and is required for receptor editing, we suggest that NF-B could be acting through IRF4 to regulate receptor editing.

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