The caspase‐derived C‐terminal fragment of βAPP induces caspase‐independent toxicity and triggers selective increase of Aβ42 in mammalian cells

Abstract

During its physiopathological maturation, the b-amyloid precursor protein undergoes several distinct proteolytic events by activities called secretases. In Alzheimer's disease, the main histological hallmark called senile plaque is clearly linked to the overproduction of the amyloid peptides Ab40 and Ab42, two highly aggregable bAPP-derived fragments generated by combined cleavages by b-and g-secretases. Recently, an alternative hydrolytic pathway was described, involving another category of proteolytic activities called caspases, responsible for the production of a 31 amino acids bAPP C-terminal fragment called C31. C31 was reported to lower the viability of N2a cells but the exact mechanisms mediating C31-toxicity remained to be established. Here we show that the transient transfection of pSV2 vector encoding C31 lowers by about 80% TSM1 neuronal cells viability. Arguing against a C31-stimulated apoptotic response, we demonstrate by combined enzymatic and immunological approaches that C31 expression did not modulate basal or staurosporineinduced caspase 3-like activity and pro-caspase-3 activation. Furthermore, C31 did not modify Bax and p53 expressions, poly-(ADP-ribose)-polymerase cleavage and cytochrome c translocation into the cytosol. However, we established that C31 overexpression triggers selective increase of Ab42 but not Ab40 production by HEK293 cells expressing wild-type bAPP751. Altogether, our data demonstrate that C31 induces a caspase-independent toxicity in TSM1 neurons and potentiates the pathogenic bAPP maturation pathway by increasing selectively Ab42 species in wild type-bAPP-expressing human cells.

Aβ induces cell death by direct interaction with its cognate extracellular domain on APP (APP 597–624)

“…We previously suggested that a component of Aβ toxicity is APP dependent, and this requires an intact caspase cleavage site in the cytoplasmic domain at position 664 of APP (12,20,38). Further, we showed that forced dimerization of APP led to increased susceptibility to cell death (27).…”

“…On the other hand, this finding would not explain why C99, which does not contain the E2 region, also forms complexes. It is possible that the transmembrane sequence or cytosolic adaptor molecules are able to facilitate APP complex formations as well.We previously suggested that a component of Aβ toxicity is APP dependent, and this requires an intact caspase cleavage site in the cytoplasmic domain at position 664 of APP (12,20,38). Further, we showed that forced dimerization of APP led to increased susceptibility to cell death (27).…”

The Role of Apoptotic Pathways in Alzheimers Disease Neurodegeneration and Cell Death

“…Both the 3 kDa C31 peptide and the Nterminus APP∆C31 generated by caspase cleavage are toxic. The C31 peptide renders N2a and HEK293T cells more susceptible to apoptotic insult staurosporine and is toxic to primary cultures of neurons or glia and neuronal cell line, TSM1 [43,71,72]. Similarly, APP∆C31 can induce cell death in a number of neuronal and non-neuronal cell lines [73].…”

Caspase‐Independent and Autophagic Programmed Cell Death

“…Furthermore, caspase-independent forms of PCD have been observed in neurodegenerative and lymphatic diseases. Thus, the caspase-derived C-terminal fragment of beta-amyloid precursor (betaAPP) induces caspase-independent toxicity in TSM1 neurons and potentiates the pathogenic betaAPP maturation pathway by increasing selectively a beta42 species in wild-type betaAPP-expressing human cells (Dumanchin-Njock et al, 2001). Complement-mediated cell death induced by rituximab in B-cell lymphoproliferative disorders is mediated in vitro by a caspase-independent mechanism involving the generation of reactive oxygen species (Bellosillo et al, 2001).…”