Biomedical subjects

Erik Helmerhorst

Publications and source records attributed to Erik Helmerhorst.

3 recordsLinked to original sources

PubMed2005

Correlation between inactive cathepsin D expression and retinal changes in mcd2/mcd2 transgenic mice.

PURPOSE: To investigate the correlation between the presence of the inactive cathepsin D (CatD) and retinal changes in mcd2/mcd2 transgenic mice. METHODS: Computational modeling was used to examine whether CatD mutants maintain competitive substrate binding. D407 cells were transfected with pcDNACatDM1 or pcDNACatDM2, containing procathepsin D (pro-CatD) with 6-bp (CatDM1) or 12-bp (CatDM2) deletions, respectively, flanking the pro-CatD cleavage site, and the aspartic protease activity of the transfected cells was measured. Subsequently, transgenic mice (mcd2/mcd2) containing CatDM2 were generated. Relative transgene copy number and transcript levels in the previously produced mcd/mcd (carrying CatDM1) and mcd2/mcd2 mice were measured by quantitative real-time PCR. Western blot analysis and aspartic protease activity were used to characterize the mutated proteins. Retinal changes were described by using color fundus photography and fluorescein angiography, histology, immunohistochemistry, and electron microscopy. RESULTS: Computational modeling of the CatDM1 and CatDM2 structures indicated that the substrate binding site was not altered. There was limited or no aspartic protease activity associated with CatDM1 and CatDM2 proteins, respectively. Mcd2/mcd2 animals contained a higher amount of inactive CatD than mcd/mcd or wild-type mice. Retinal abnormalities in mcd2/mcd2 mice developed at 3 months of age, earlier than in mcd/mcd mice. These changes included hypopigmentation, hyperfluorescence, retinal pigment epithelial (RPE) cell depigmentation or clumping, cell proliferation, and pleomorphism. Proliferating cells were identified as being of RPE origin. CONCLUSIONS: This study demonstrated a correlation between the presence of the inactive CatD in RPE cells and the development of ophthalmoscopic, cellular, and histologic changes in the retina.

Animals↗

PubMed2002

Alzheimer's beta-amyloid peptides compete for insulin binding to the insulin receptor.

The amyloid-beta (Abeta) peptide is neurotoxic and associated with the pathology of Alzheimer's disease (AD). We investigated the effect of Abeta peptides on insulin binding to the insulin receptor because it is known that (1) Abeta and insulin are both amyloidogenic peptides sharing a common sequence recognition motif, (2) Abeta and insulin are substrates for the same insulin degrading enzyme, and (3) impaired glucose metabolism is a characteristic event in the pathology of AD. We discovered that Abeta(1-40) and Abeta(1-42,) the main physiological forms, reduced insulin binding and receptor autophosphorylation. The reduction in binding was caused by a decrease in the affinity of insulin binding to the insulin receptor. This reduction was independent of the receptor concentration. The reverse, control peptide Abeta(40-1) did not reduce insulin binding or insulin receptor autophosphorylation. These results demonstrate that Abeta is a direct competitive inhibitor of insulin binding and action. We speculate that the increased levels of Abeta in Alzheimer's disease may be linked to the associated insulin resistance that has been observed previously in this disease.

Alzheimer Disease↗

PubMedDate not supplied

Insulin decreases the secretion of apoB-100 from hepatic HepG2 cells but does not decrease the secretion of apoB-48 from intestinal CaCo-2 cells.

We compared the acute effect of insulin on the human colonic intestinal epithelial cell line CaCo-2 and the transformed human hepatic cell line HepG2. Over 24 h, 100 nM and 10 microM insulin significantly inhibited the secretion of apolipoprotein (apo) B-100 from HepG2 cells to 63 and 49% of control, respectively. Insulin had no effect on the secretion of apoB-48 from CaCo-2 cells. There was no effect of insulin on the cholesterol ester or free cholesterol concentrations in HepG2 or CaCo-2 cells. HepG2 and CaCo-2 cells bound insulin with high affinity, leading to similar stimulation of insulin receptor protein tyrosine kinase activation. Protein kinase C or mitogen-activated protein kinase activity in the presence or absence of insulin was not correlated with apoB-48 production in CaCo-2 cells. Therefore, insulin acutely decreases the secretion of apoB-100 in hepatic HepG2 cells, but does not acutely modulate the production or secretion of apoB-48 from CaCo-2 intestinal cells.

Apolipoprotein B-100↗