Early upregulation of cytosolic phospholipase Aα in motor neurons is induced by misfolded SOD1 in a mouse model of amyotrophic lateral sclerosis.

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal multifactorial neurodegenerative disease characterized by the selective death of motor neurons. Cytosolic phospholipase A alpha (cPLAα) upregulation and activation in the spinal cord of ALS patients has been reported. We have previously shown that cPLAα upregulation in the spinal cord of mutant SOD1 transgenic mice (SOD1) was detected long before the development of the disease, and inhibition of cPLAα upregulation delayed the disease's onset. The aim of the present study was to determine the mechanism for cPLAα upregulation.

METHODS

Immunofluorescence analysis and western blot analysis of misfolded SOD1, cPLAα and inflammatory markers were performed in the spinal cord sections of SOD1 transgenic mice and in primary motor neurons. Over expression of mutant SOD1 was performed by induction or transfection in primary motor neurons and in differentiated NSC34 motor neuron like cells.

RESULTS

Misfolded SOD1 was detected in the spinal cord of 3 weeks old mutant SOD1 mice before cPLAα upregulation. Elevated expression of both misfolded SOD1 and cPLAα was specifically detected in the motor neurons at 6 weeks with a high correlation between them. Elevated TNFα levels were detected in the spinal cord lysates of 6 weeks old mutant SOD1 mice. Elevated TNFα was specifically detected in the motor neurons and its expression was highly correlated with cPLAα expression at 6 weeks. Induction of mutant SOD1 in primary motor neurons induced cPLAα and TNFα upregulation. Over expression of mutant SOD1 in NSC34 cells caused cPLAα upregulation which was prevented by antibodies against TNFα. The addition of TNFα to NSC34 cells caused cPLAα upregulation in a dose dependent manner.

CONCLUSIONS

Motor neurons expressing elevated cPLAα and TNFα are in an inflammatory state as early as at 6 weeks old mutant SOD1 mice long before the development of the disease. Accumulated misfolded SOD1 in the motor neurons induced cPLAα upregulation via induction of TNFα.