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Biomedical subjects

B Lamothe

Publications and source records attributed to B Lamothe.

11 recordsLinked to original sources
PubMed2001

IGF-1 receptor as an alternative receptor for metabolic signaling in insulin receptor-deficient muscle cells.

We have derived skeletal muscle cell lines from wild-type (wt) and insulin receptor (IR) knockout mice to unravel the metabolic potential of IGF-1 receptor (IGF-1R). Both wt and IR(-/-) myoblasts differentiated into myotubes with similar patterns of expression of muscle-specific genes such as MyoD, myogenin and MLC1A indicating that IR is not required for this process. Binding of 125I-IGF-1 on wt and IR(-/-) myotubes was similar showing that IGF-1R was not upregulated in the absence of IR. Stimulation of IR(-/-) myotubes with IGF-1 (10(-10) to 10(-7) M) increased glucose uptake and incorporation into glycogen, induced IRS-1 phosphorylation and activated PI 3-kinase and MAP kinase, two enzymes of major signaling pathways. These effects were comparable to those obtained with wt myotubes using insulin or IGF-1 or with IR(-/-) myotubes using insulin at higher concentrations. This study provides a direct evidence that IGF-1R can represent an alternative receptor for metabolic signaling in muscle cells.

Animals↗
PubMed2001

Endocrine pancreas in insulin receptor-deficient mouse pups.

Insulin receptor (IR)-deficient pups rapidly become hyperglycemic and hyperinsulinemic and die of diabetic ketoacidosis within a few days. Immunocytochemical analysis of the endocrine pancreas revealed that IR deficiency did not alter islet morphology or the number of beta-, alpha-, delta-, and pancreatic polypeptide (PP) cells. The lack of IR did not result in major changes in the expression of islet hormone genes or of beta-cell-specific marker genes encoding pancreas duodenum homeobox-containing transcription factor-1 (PDX-1), glucokinase (GCK), and GLUT2, as shown by reverse transcriptase-polymerase chain reaction analysis. The serum glucagon levels in IR-deficient and nondiabetic littermates were comparable. Finally, total insulin content in the pancreas of IR-deficient pups was gradually depleted, indicating sustained insulin secretion, not compensated for by increased insulin biosynthesis. These findings are discussed in light of recent results suggesting a role of IR in beta-cell function.

Animals↗
PubMed2000

Current developments and future prospects for HIV gene therapy using interfering RNA-based strategies.

Acquired immunodeficiency syndrome (AIDS) is a slow, progressive, degenerative disease of the human immune system, ultimately leading to premature death of the patient. This disease is primarily caused by human immunodeficiency virus type-1 (HIV-1). The major targets of HIV infection are blood cells, namely lymphocytes and macrophages. While the immune response fails to eliminate the infected cells, the virus continues to spread. The purpose of HIV gene therapy is to provide "anti-HIV" genes to cells that are susceptible to HIV infection. Anti-HIV genes may be designed to express RNAs or proteins that interfere with the function of viral or cellular RNA(s)/protein(s), thereby inhibiting virus replication. Whereas interfering proteins may be cytotoxic and/or immunogenic, interfering RNAs are not. Interfering protein-based strategies requiring inducible gene expression (under the control of HIV regulatory proteins) can only be designed to block steps subsequent to the viral regulatory protein production. In contrast, interfering RNAs can be produced in a constitutive manner, which further enhances their antiviral activity and allows one to design strategies to inhibit virus replication before viral regulatory protein production occurs. Thus, interfering RNAs are of particular interest and are the focus of this review. Genes expressing interfering RNAs were designed to inhibit syncytium formation to prevent the death of the gene-modified cells. Strategies may also be developed to prevent gene-modified cells from becoming infected by HIV or from supporting HIV replication. Genes expressing interfering RNAs have been designed to inhibit HIV-1 entry and to cleave the incoming virion RNA, thus blocking virus replication before provirus DNA synthesis can be completed. A number of genes were also designed to express interfering RNAs that inhibit HIV replication at a post-integration step, by inhibiting the function of HIV RNAs or proteins produced in the infected cell. Also in development are anti-HIV genes that produce RNAs that would not only inhibit HIV replication in the gene-modified cell, but also prevent HIV RNA packaging and/or reverse transcription such that the progeny virus produced would be non-infectious. Further refinements to these strategies may lead to the development of "self-propagating" anti-HIV genes. These genes would express interfering RNAs that not only inhibit virus replication in the cell and prevent HIV RNA packaging and/or reverse transcription in the progeny virus, but also make use of the HIV itself to deliver the anti-HIV gene(s) to other cells. Thus, more and more cells susceptible to HIV infection would become resistant. Such "self-propagation" of anti-HIV-1 genes would only occur in cells that are susceptible to HIV infection, and would continue to take place for as long as HIV exists in the body.

Clinical Trials as Topic↗
PubMed1998

Genetic engineering in mice: impact on insulin signalling and action.

The expression of a number of genes encoding key players in insulin signalling and action, including insulin, insulin receptor (IR), downstream signalling molecules such as insulin receptor substrate-1 (IRS-1) and IRS-2, glucose transporters (GLUT4, GLUT2) and important metabolic enzymes such as glucokinase, has now been altered in transgenic or knockout mice. Such mice presented with phenotypes ranging from mild defects, revealing complementarity between key molecules or pathways, to severe diabetes with ketoacidosis and early postnatal death. Insulin action could also be improved by overproduction of proteins acting at regulatory steps. The development of diabetes by combining mutations, which alone do not lead to major metabolic alterations, validated the 'diabetogenes' concept of non-insulin-dependent diabetes mellitus. Genes encoding insulin-like growth factors (IGF-I and IGF-II) and their type I receptor (IGF-IR) have also been disrupted. It appears that although IR and IGF-IR are both capable of metabolic and mitogenic signalling, they are not fully redundant. However, IR could replace IGF-IR if efficiently activated by IGF-II. Studies with cell lines lacking IR or IGF-IR lend support to such conclusions. Concerning the issues of specificity and redundancy, studies with cell lines derived from IRS-1-deficient mice showed that IRS-1 and IRS-2 are also not completely interchangeable.

Animals↗
PubMed1998

Insulin receptor-deficient cells as a new tool for dissecting complex interplay in insulin and insulin-like growth factors.

Cell systems derived from knockout mice for the insulin receptor (IR) or the IGF-1 receptor (IGF-1R) represent unique tools for dissecting complex interplay in the actions of insulin and insulin-like growth factors through their cognate versus non-cognate receptor. In this study, we used a fibroblast cell line derived from IR-deficient mice to investigate metabolic and mitogenic effects of IGF-1 and insulin. IGF-1 was able to stimulate glucose uptake, glucose incorporation into glycogen and thymidine incorporation in such cells. Phosphatidylinositol 3-kinase and mitogen-activated protein kinase, two enzymes of major metabolic-mitogenic signaling pathways, were activated upon stimulating these cells with IGF-1. All these effects were also achieved when IR-deficient cells were stimulated with insulin. Thus, IGF-1R can represent an alternative receptor through which insulin might exert some of its effects.

Animals↗
PubMed1998

Genetic manipulation of insulin action and beta-cell function in mice.

Transgenic and gene targeting approaches have now been applied to a number of genes in order to investigate the metabolic disorders that would result by manipulating insulin action or pancreatic beta-cell function in the mouse. The availability of such mutant mice will allow in the future to develop animal models in which the pathophysiologies resulting from polygenic defects might be reconstituted and studied in detail. Such animal models hopefully will lead to better understanding of complex polygenic diseases such as non-insulin-dependent diabetes mellitus (NIDDM).

Animals↗
PubMed1997

Genetically engineered mice as animal models for NIDDM.

Genetically engineered animals carrying defined alterations in their genome can represent invaluable tools for better understanding complex polygenic diseases such as non-insulin-dependent diabetes mellitus (NIDDM) at the molecular level. The structure or expression of a number of genes potentially involved in insulin action or pancreatic beta-cell function have recently been altered in the mouse using transgenic or gene-targeting approaches. The obtention of such mice is the first step towards the development of animal models carrying multiple gene defects which would be very useful in NIDDM research.

Animals↗
PubMed1996

Reexamining interaction of the SH2 domains of SYP and GAP with insulin and IGF-1 receptors in the two-hybrid system.

Direct interaction of effector proteins such as the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), SYP (SH2-domain-containing tyrosine phosphatase) and GAP (Ras-GTPase activating protein) with the insulin receptor (IR) and insulin-like growth factor-1 (IGF-1) type 1 receptor (IGF-1R) has been reported in some studies. Interaction of SYP and GAP with IR and IGF-1R was re-investigated here in the two-hybrid system by assessing his3/lacZ activation in S. cerevisiae. The experiments were performed with the cytoplasmic beta domain of IR and IGF-1R and various SH2-subdomains of SYP and GAP. None of the subdomains of SYP and GAP tested were able to activate his3/lacZ, whereas these reporter genes were strongly activated when p85 was used as we have recently shown. Thus, interaction of SYP and GAP with IR and IGF-1R, if any, would be weak and/or transient as compared to that of p85.

Bacterial Proteins↗
PubMed1996

Targeted disruption of the insulin receptor gene in the mouse results in neonatal lethality.

Targeted disruption of the insulin receptor gene (Insr) in the mouse was achieved using the homologous recombination approach. Insr+/- mice were normal as shown by glucose tolerance tests. Normal Insr-/- pups were born at expected rates, indicating that Insr can be dispensable for intrauterine development, growth and metabolism. However, they rapidly developed diabetic ketoacidosis accompanied by a marked post-natal growth retardation (up to 30-40% of littermate size), skeletal muscle hypotrophy and fatty infiltration of the liver and they died within 7 days after birth. Total absence of the insulin receptor (IR), demonstrated in the homozygous mutant mice, also resulted in other metabolic disorders: plasma triglyceride level could increase 6-fold and hepatic glycogen content could be five times less as compared with normal littermates. The very pronounced hyperglycemia in Insr-/- mice could result in an increased plasma insulin level of up to approximately 300 microU/ml, as compared with approximately 25 microU/ml for normal littermates. However, this plasma level was still unexpectedly low when compared with human infants with leprechaunism, who lack IR but who could have extremely high insulinemia (up to > 4000 microU/ml). The pathogenesis resulting from a null mutation in Insr is discussed.

Animals↗
PubMed1995

Interaction of p85 subunit of PI 3-kinase with insulin and IGF-1 receptors analysed by using the two-hybrid system.

Interaction of the p85 subunit of PI 3-kinase with the insulin receptor (IR) and the IGF-1 receptor (IGF-1R) was investigated using the two-hybrid system by assessing for his3 and lacZ activation in S. cerevisiae. The experiments were performed with the cytoplasmic beta domain (wild type or mutated) of IR and IGF-1R and p85 or its subdomains (N + C-SH2, N-SH2, C-SH2, SH3 + N-SH2). The results of his3 activation indicated that p85, N + C-SH2 and C-SH2 interact with both IR beta and IGF-1R beta, whereas N-SH2 and SH3 + N-SH2 interact only with IR beta. Interaction of p85 and N+C-SH2 with IR beta (delta C-43) or IGF-1R beta(delta C-43) in which the C-terminal 43 amino acids (including the YXXM motif) were deleted, persisted. The internal binding site thus revealed was not altered by further mutating Y960/F for IR or Y950/F for IGF-1R. Activation of lacZ upon interaction of p85 with IR beta(delta C-43) was 4-fold less as compared to IR beta. This activation with p85 and IGF-1R beta was 4-fold less as compared to IR beta and was somewhat increased (2-fold) for IGF-1R beta (delta C-43). Thus, the C-terminal domain in IGF-1R appears to exert a negative control on binding of p85 thereby providing a possible regulatory mechanism for direct activation of the PI 3-kinase pathway.

Amino Acid Sequence↗