Mycoplasmas are frequent contaminants of cell cultures. Contamination leads to altered synthetic and metabolic pathways. We have found that contamination of
neuroblastoma SH-SY5Y cells by a strain of Mycoplasma hyorhinis derived from SH-SY5Y cell culture (NDMh) leads to increased levels of
calpastatin (the endogenous inhibitor of the Ca(2+)-dependent
protease,
calpain) in NDMh-infected cells. We have now examined effects of
amyloid-β-
peptide (Aβ) (central to the pathogenesis of
Alzheimer's disease) on uncontaminated (clean) and NDMh-infected SH-SY5Y cells. Aβ was toxic to clean cells, resulting in necrotic cell damage. Aβ treatment led to activation of
calpain and enhanced proteolysis, cell swelling, cell membrane permeability to
propidium iodide (PI) (without nuclear apoptotic changes), and diminished mitochondrial
enzyme activity (XTT reduction). Aβ-toxicity was attenuated in the high
calpastatin-containing NDMh-infected cells, as shown by inhibition of
calpain activation and activity, no membrane permeability, normal cell morphology, and maintenance of mitochondrial
enzyme activity (similar to attenuation of Aβ-toxicity in non-infected cells overexpressing
calpastatin following
calpastatin-plasmid introduction into the cells). By contrast,
staurosporine affected both clean and infected cells, causing apoptotic damage (cell shrinkage, nuclear apoptotic alterations,
caspase-3 activation and
caspase-promoted proteolysis, without PI permeability, and without effect on XTT reduction). The results indicate that mycoplasma protects the cells against certain types of insults involving
calpain. The ratio of
calpastatin to
calpain is an important factor in the control of
calpain activity. Exogenous pharmacological means, including
calpastatin-based inhibitors, have been considered for
therapy of various diseases in which
calpain is implicated. Mycoplasmas provide the first naturally occurring
biological system that upregulates the endogenous
calpain inhibitor, and thus may be of interest in devising treatments for some disorders, such as
neurodegenerative diseases.