Different early ER-stress responses in the CLN8(mnd) mouse model of neuronal ceroid lipofuscinosis.

Neuronal ceroid lipofuscinoses (NCLs) are a group of inherited neurodegenerative disorders characterized by epilepsy, progressive motor and cognitive decline, blindness, and by the accumulation of autofluorescent lipopigment. Late-infantile onset forms (LINCL) include those linked to mutations in CLN8 gene, encoding a transmembrane protein at the endoplasmic reticulum (ER). In the motor neuron degeneration (mnd) mouse model of the CLN8-LINCL (CLN8(mnd)), we carried out an analysis of ER stress-related molecules in CNS structures that exhibit a variable rate of disease progression (early retinal degeneration and delayed brain and motoneuron dysfunction). At the presymptomatic state of 1-month-old CLN8(mnd) mice, we found an upregulation of GRP78 and activation of the transcription factor-6 (ATF6) in all structures examined, an activation of a CHOP-dependent pathway in the cerebellum, hippocampus and retina, a caspase-12-dependent pathway in the retina and no activation of these two pathways in the cerebral cortex and spinal cord. An increased CHOP expression was detected in the cortex and spinal cord at the early symptomatic state (4 months). Caspase-3 cleavage occurred presymptomatically in the cerebellum, hippocampus and retina, and symptomatically in the cerebral cortex and spinal cord. We also monitored activation of NF-κB, which is engaged in the alarming phase of ER stress, together with increased levels of TRAF2, TNF-α and TNFR1, and no activation of ASK-1/JNK signalling pathway, all over mnd structures. The results suggest that early ER-stress responses distinctly combined and ER-stress pathways integrated with inflammatory responses may contribute to the progression of the CLN8(mnd) disease in CNS structures.

Retinal oxidation, apoptosis and age- and sex-differences in the mnd mutant mouse, a model of neuronal ceroid lipofuscinosis.

Retinal degeneration is an early and progressive event in many forms of neuronal ceroid lipofuscinoses (NCLs), a heterogeneous group of neurodegenerative disorders with unknown pathogenesis. We here used the mutant motor neuron degeneration (mnd) mouse, a late-infantile NCL variant, to investigate the retinal oxidative state and apoptotic cell death as a function of age and sex. Total superoxide dismutase (SOD) activities and thiobarbituric acid-reactive substance (TBARS) levels revealed progressive increases in retinal oxyradicals and lipid peroxides of mnd mice of both sexes. Female mnd retinas showed a higher oxidation rate and consistently exhibited the 4-hydroxy-2-nonenal (4-HNE)-adducts staining and advanced histopathologic profile when compared to male mnd retinas matched for age. In situ DNA fragmentation (TUNEL staining) appeared in the outer nuclear layer (ONL) as early as 1 month of age. At 4 months, there were more intense and numerous TUNEL-positive cells in the same layer and in the inner nuclear (INL) and ganglion cell (GCL) layers; whereas at 8 months TUNEL staining was restricted to a few scattered cells in the INL and GCL, when a severe retinal cell loss had occurred. Caspase-3 activation confirmed apoptotic demise and its processing turned out to be higher in mnd females than males. These results demonstrate the involvement of oxidation and apoptotic processes in mnd mouse retinopathy and highlight sex-related differences in retinal vulnerability to oxidative stress and damage.