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Mutation of profilin 1 (PFN1) can cause amyotrophic lateral sclerosis (ALS). To assess how PFN1 mutation causes the disease, we created transgenic rats with human genomic DNA that harbors both the coding and the regulatory sequences of the human PFN1 gene. Selected transgenic lines expressed human PFN1 with or without the pathogenic mutation C71G at a moderate and a comparable level and in the similar pattern of spatial and temporal expression to rat endogenous PFN1. The artificial effects of arbitrary transgene expression commonly observed in cDNA transgenic animals were minimized in PFN1 transgenic rats. Expression of the mutant, but not the wild type, human PFN1 in rats recapitulated the cardinal features of ALS including the progressive loss of motor neurons and the subsequent denervation atrophy of skeletal muscles. Detergent‐insoluble PFN1 inclusions were detected as the first pathology in otherwise asymptomatic transgenic rats expressing mutant human PFN1. The findings suggest that protein aggregation is involved in the neurodegeneration of ALS associated with PFN1 mutation. The resulting rat model is useful to mechanistic study on the ALS. [ABSTRACT FROM AUTHOR]

Pathogenic mutation of ubiquilin 2 ( UBQLN2) causes neurodegeneration in amyotrophic lateral sclerosis and frontotemporal lobar degeneration. How UBQLN2 mutations cause the diseases is not clear. While over-expression of UBQLN2 with pathogenic mutation causes neuron death in rodent models, deletion of the Ubqln2 in rats has no effect on neuronal function. Previous findings in animal models suggest that UBQLN2 mutations cause the diseases mainly through a gain rather than a loss of functions. To examine whether the toxic gain in UBQLN2 mutation is related to the enhancement of UBQLN2 functions, we created new transgenic rats over-expressing wild-type human UBQLN2. Considering that human UBQLN2 may not function properly in the rat genome, we also created transgenic rats over-expressing rat's own Ubqln2. When over-expressed in rats, both human and rat wild-type Ubqln2 caused neuronal death and spatial learning deficits, the pathologies that were indistinguishable from those observed in mutant UBQLN2 transgenic rats. Over-expressed wild-type UBQLN2 formed protein inclusions attracting the autophagy substrate sequestosome-1 and the proteasome component 26S proteasome regulatory subunit 7. These findings suggest that excess UBQLN2 is toxic rather than protective to neurons and that the enhancement of UBQLN2 functions is involved in UBQLN2 pathogenesis. [ABSTRACT FROM AUTHOR]

Mutation in TAR DNA binding protein 43 ( TDP-43) is a causative factor of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Neurodegeneration may not require the presence of pathogenic TDP-43 in all types of relevant cells. Rather, expression of pathogenic TDP-43 in neurons or astrocytes alone is sufficient to cause cell-autonomous or non-cell-autonomous neuron death in transgenic rats. How pathogenic TDP-43 in astrocytes causes non-cell-autonomous neuron death, however, is not clear. Here, we examined the effect of pathogenic TDP-43 on gene expression in astrocytes. Microarray assay revealed that pathogenic TDP-43 in astrocytes preferentially altered expression of the genes encoding secretory proteins. Whereas neurotrophic genes were down-regulated, neurotoxic genes were up-regulated. Representative genes Lcn2 and chitinase-3-like protein 1 were markedly up-regulated in astrocytes from primary culture and intact transgenic rats. Furthermore, synthetic chitinase-3-like protein 1 induced neuron death in a dose-dependent manner. Our results suggest that TDP-43 pathogenesis is associated with the simultaneous induction of multiple neurotoxic genes in astrocytes, which may synergistically produce adverse effects on neuronal survival and contribute to non-cell-autonomous neuron death. [ABSTRACT FROM AUTHOR]

Protein aggregation is a common feature of several neurodegenerative diseases, including amyotrophic lateral sclerosis ( ALS) and frontotemporal lobar degeneration. How protein aggregates are formed and contribute to neurodegeneration, however, is not clear. Mutation of Ubiquilin 2 ( UBQLN2) has recently been linked to ALS and frontotemporal lobar degeneration. Therefore, we examined the effect of ALS-linked UBQLN2 mutation on endoplasmic reticulum-associated protein degradation ( ERAD). Compared to its wild-type counterpart, mutated UBQLN2 caused greater accumulation of the ERAD substrate Hong Kong variant of α-1-antitrypsin, although ERAD was disturbed by both UBQLN2 over-expression and knockdown. Also, UBQLN2 interacted with ubiquitin regulatory X domain-containing protein 8 ( UBXD8) in vitro and in vivo, and this interaction was impaired by pathogenic mutation of UBQLN2. As UBXD8 is an endoplasmic membrane protein involved in the translocation of ubiquitinated ERAD substrates, UBQLN2 likely cooperates with UBXD8 to transport defective proteins from the endoplasmic reticulum to the cytosol for degradation, and this cell-protective function is disturbed by pathogenic mutation of UBQLN2. [ABSTRACT FROM AUTHOR]

Mutation of Tar DNA-binding protein 43 (TDP-43) is linked to amyotrophic lateral sclerosis. Although astrocytes have important roles in neuron function and survival, their potential contribution to TDP-43 pathogenesis is unclear. Here, we created novel lines of transgenic rats that express a mutant form of human TDP-43 (M337V substitution) restricted to astrocytes. Selective expression of mutant TDP-43 in astrocytes caused a progressive loss of motor neurons and the denervation atrophy of skeletal muscles, resulting in progressive paralysis. The spinal cord of transgenic rats also exhibited a progressive depletion of the astroglial glutamate transporters GLT-1 and GLAST. Astrocytic expression of mutant TDP-43 led to activation of astrocytes and microglia, with an induction of the neurotoxic factor Lcn2 in reactive astrocytes that was independent of TDP-43 expression. These results indicate that mutant TDP-43 in astrocytes is sufficient to cause non-cell-autonomous death of motor neurons. This motor neuron death likely involves deficiency in neuroprotective genes and induction of neurotoxic genes in astrocytes. [ABSTRACT FROM AUTHOR]

Protein inclusion is a prominent feature of neurodegenerative diseases including frontotemporal lobar degeneration ( FTLD) that is characterized by the presence of ubiquitinated TDP-43 inclusion. Presence of protein inclusions indicates an interruption to protein degradation machinery or the overload of misfolded proteins. In response to the increase in misfolded proteins, cells usually initiate a mechanism called unfolded protein response ( UPR) to reduce misfolded proteins in the lumen of endoplasmic reticules. Here, we examined the effects of mutant TDP-43 on the UPR in transgenic rats that express mutant human TDP-43 restrictedly in the neurons of the forebrain. Over-expression of mutant TDP-43 in rats caused prominent aggregation of ubiquitin and remarkable fragmentation of Golgi complexes prior to neuronal loss. While ubiquitin aggregates and Golgi fragments were accumulating, neurons expressing mutant TDP-43 failed to up-regulate chaperones residing in the endoplasmic reticules and failed to initiate the UPR. Prior to ubiquitin aggregation and Golgi fragmentation, neurons were depleted of X-box-binding protein 1 ( XBP1), a key player of UPR machinery. Although it remains to determine how mutation of TDP-43 leads to the failure of the UPR, our data demonstrate that failure of the UPR is implicated in TDP-43 pathogenesis. [ABSTRACT FROM AUTHOR]