Biomedical subjects

Hugo L Fernandez

Publications and source records attributed to Hugo L Fernandez.

3 recordsLinked to original sources

PubMed2005

Mu-calpain is functionally required for alpha-processing of Alzheimer's beta-amyloid precursor protein.

Alzheimer's beta-amyloid precursor protein (APP) is normally processed by an unidentified alpha-secretase. A unique feature of this protease is its high sensitivity to phorbol esters, yet the mechanism involved is unclear. We have previously reported that phorbol 12,13-dibutyrate (PDBu) activates calpain, a Ca2+-dependent protease, and PDBu-induced release of APPs (secreted APP) is sensitive to calpain inhibitors, suggesting that calpain is involved in APP alpha-processing. In the present study, we found that PDBu markedly promoted the expression of both mu- and m-calpains in cultured fibroblasts. Dose-response and time course studies revealed that mu-calpain was more sensitive to PDBu than m-calpain and the temporal course of the mu-calpain change coincides better with that of APPs release. Moreover, the stimulatory effect of PDBu on mu-calpain was selectively blocked by mu-calpain-specific siRNA (small interference RNA) and the blockage was accompanied by a concomitant decrease in APPs release. In contrast, m-calpain siRNA did not affect APPs release significantly. Measurement of amyloid beta protein (Abeta) release in the mu-calpain siRNA-treated cells indicated that Abeta40 and Abeta42 levels inversely changed in relation to APPs, and the changes in Abeta42 were more prominent than in Abeta40. Together, these data suggest that calpain, particularly mu-calpain, is a potential candidate for alpha-secretase in the regulated APP alpha-processing, and that changes in this protease can affect the outcome of the overall APP processing.

Alzheimer Disease↗

PubMed2004

Stimulation of beta-amyloid precursor protein alpha-processing by phorbol ester involves calcium and calpain activation.

Normal processing of Alzheimer's beta-amyloid precursor protein (APP) is markedly stimulated by phorbol esters, but the underlying mechanisms have yet to be fully understood. In this study, we observed that: (a) Phorbol 12,13-dibutyrate (PDBu)-stimulated APP secretion in cultured SH-SY5Y neuroblastoma and fibroblast cells was blocked by EGTA and calpain inhibitors in a concentration-dependent manner, but not by other protease inhibitors. (b) Secretion of fibronectin, another secretory protein tested for comparison, was enhanced by PDBu, but insensitive to calpain inhibitors. (c) PDBu stimulated intracellular calpain activity as measured by the hydrolysis of a fluorogenic calpain substrate. (d) PDBu also induced rapid proteolysis of two endogenous substrates of calpains, i.e., tau and microtubule-associated protein-2 (MAP-2) and the proteolysis was blocked by EGTA and calpain inhibitors. Taken together, these results suggest that stimulation of APP alpha-processing by PDBu is through a mechanism that involves the activation of Ca(2+) and, most notably, calpain. The implications of the findings are discussed in relation to the regulatory mechanism of APP alpha-processing.

Amyloid beta-Protein Precursor↗

PubMed2002

Implications of amyloid precursor protein and subsequent beta-amyloid production to the pharmacotherapy of Alzheimer's disease.

Alzheimer's disease is the most common type of dementia in older people. It is highly prevalent, affecting 35-45% of those aged 85 years or older. This disease has devastating consequences to patients, their families, caregivers, and the health care system. Much has been learned about its pathobiology, which has led to the beta-amyloid (Abeta) hypothesis. This hypothesis continues to be the predominant postulate of the pathobiology of Alzheimer's disease. Under this hypothesis, abnormal accumulation of Abeta is followed by a cascade of neurotoxic effects, which eventually result in neurodegeneration and development of Alzheimer's disease. This is thought to be the result of altered processing of the amyloid precursor protein (APP), preferentially by beta- and gamma-secretase enzymes rather than nonamyloidogenic processing by alpha-secretase. The growing body of knowledge regarding the processing of APP to various forms of Abeta has resulted in new approaches to the investigation of putative anti-Alzheimer's disease compounds, including immune-based therapies and various agents that can positively affect APP processing.

Alzheimer Disease↗