Endogenous macrophage migration inhibitory factor reduces the accumulation and toxicity of misfolded SOD1 in a mouse model of ALS

Abstract

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease characterized by the loss of upper and lower motor neurons in the brain and spinal cord. It has been suggested that the toxicity of mutant SOD1 results from its misfolding and accumulation on the cytoplasmic faces of intracellular organelles, including the mitochondria and endoplasmic reticulum (ER) of ALS-affected tissues. Recently, macrophage migration inhibitory factor (MIF) was shown to directly inhibit the accumulation of misfolded SOD1 and its binding to intracellular membranes, but the role of endogenous MIF in modulating SOD1 misfolding in vivo remains unknown. To elucidate this role, we bred MIF-deficient mice with SOD1 G85R mice, which express a dismutase-inactive mutant of SOD1 and are considered a model of familial ALS. We found that the accumulation of misfolded SOD1, its association with mitochondrial and ER membranes, and the levels of sedimentable insoluble SOD1 aggregates were significantly higher in the spinal cords of SOD1 G85R -MIF −/− mice than in their SOD1 G85R -MIF +/+ littermates. Moreover, increasing MIF expression in neuronal cultures inhibited the accumulation of misfolded SOD1 and rescued from mutant SOD1-induced cell death. In contrast, the complete elimination of endogenous MIF accelerated disease onset and late disease progression and shortened the lifespan of the SOD1 G85R mutant mice. These findings indicate that MIF plays a significant role in the folding and misfolding of SOD1 in vivo, and they have implications for the potential therapeutic role of upregulating MIF within the nervous system to modulate the selective accumulation of misfolded SOD1.ALS | mutant SOD1 mouse | mutant SOD1 | misfolded SOD1 | MIF

HSPB1 mutations causing hereditary neuropathy in humans disrupt non-cell autonomous protection of motor neurons

“…13.25 ± 3.05% of wild type astrocytes were positive for mHSPB1, whereas 37.40 ± 3.18% of SOD1(G93A) astrocytes were positive for mHSPB1 (Figure 2A, 2B). Co-staining, with antibodies specific to misfolded SOD1 (47–51), revealed that SOD1 and mHSPB1 are visualized in the cytoplasm, and that 41.03 ± 3.25% of mHSPB1 positive astrocytes were also positive for misfolded SOD1.…”

“…The blots were then incubated with primary antibodies against human HSPB1, mHSPB1, SOD1, misfolded SOD1 or Tubulin for 1 hour at room temperature. The antibody against misfolded SOD1 has been previously described to be specific to human SOD1 under denaturing conditions and specific for mutant SOD1 isoforms under non-denaturing conditions (47–51). Blots were then washed 3 times with TBS-T, and incubated with secondary antibody for 1 hour at room temperature, and then scanned using a Licor Odyssey Classic.…”

The Dichotomic Role of Macrophage Migration Inhibitory Factor in Neurodegeneration

“…Several in vitro and in vivo studies have shown that MIF can inhibit the accumulation of misfolded SOD1 [36,39]. MIF can regulate both intracellular and extracellular pathways.…”

“…In particular, the ability of MIF to suppress the toxicity of SOD1 misfolded in motor neuron-like cells may be due to changes in the aggregation model from amyloid aggregates to amorphous aggregates [36]. In particular, in in vitro studies, MIF chaperone activity inhibits the formation and toxicity of misfolded SOD1 amyloid aggregates, when overexpressed in neuroblastoma cell lines such as SH-SY5Y or mouse motor neuron-like hybrid cell line NSC-34 differentiable in motor neurons [36,39]. Studies in animal models of ALS have validated the potential beneficial effects of endogenous MIF [39,41].…”

“…In particular, in in vitro studies, MIF chaperone activity inhibits the formation and toxicity of misfolded SOD1 amyloid aggregates, when overexpressed in neuroblastoma cell lines such as SH-SY5Y or mouse motor neuron-like hybrid cell line NSC-34 differentiable in motor neurons [36,39]. Studies in animal models of ALS have validated the potential beneficial effects of endogenous MIF [39,41]. Mice with mutant SOD1 genes that were knocked down for MIF exhibited higher amounts of misfolded SOD1 in the spinal cord, along with an accelerated onset of the disease and reduced the lifespan as compared to the MIF wild-type control group [39,41].…”