Abstract
BackgroundCytoplasmic inclusions of transactive response DNA binding protein of 43 kDa (TDP-43) in neurons and astrocytes are a feature of some neurodegenerative diseases, such as frontotemporal lobar degeneration with TDP-43 (FTLD-TDP) and amyotrophic lateral sclerosis (ALS). However, the role of TDP-43 in astrocyte pathology remains largely unknown.MethodsTo investigate whether TDP-43 overexpression in primary astrocytes could induce inflammation, we transfected primary astrocytes with plasmids encoding Gfp or TDP-43-Gfp. The inflammatory response and upregulation of PTP1B in transfected cells were examined using quantitative RT-PCR and immunoblot analysis. Neurotoxicity was analysed in a transwell coculture system of primary cortical neurons with astrocytes and cultured neurons treated with astrocyte-conditioned medium (ACM). We also examined the lifespan, performed climbing assays and analysed immunohistochemical data in pan-glial TDP-43-expressing flies in the presence or absence of a Ptp61f RNAi transgene.ResultsPTP1B inhibition suppressed TDP-43-induced secretion of inflammatory cytokines (interleukin 1 beta (IL-1β), interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF-α)) in primary astrocytes. Using a neuron-astrocyte coculture system and astrocyte-conditioned media treatment, we demonstrated that PTP1B inhibition attenuated neuronal death and mitochondrial dysfunction caused by overexpression of TDP-43 in astrocytes. In addition, neuromuscular junction (NMJ) defects, a shortened lifespan, inflammation and climbing defects caused by pan-glial overexpression of TDP-43 were significantly rescued by downregulation of ptp61f (the Drosophila homologue of PTP1B) in flies.ConclusionsThese results indicate that PTP1B inhibition mitigates the neuronal toxicity caused by TDP-43-induced inflammation in mammalian astrocytes and Drosophila glial cells.
Highlights
Cytoplasmic inclusions of transactive response DNA binding protein of 43 kDa (TDP-43) in neurons and astrocytes are a feature of some neurodegenerative diseases, such as frontotemporal lobar degeneration with TDP-43 (FTLD-TDP) and amyotrophic lateral sclerosis (ALS)
In line with this evidence, we observed that TDP-43 overexpression in primary astrocytes upregulated the expression of inflammatory genes (Il-1b, Il-6, Lcn2, iNOS, or Nf-κb) (Fig. 1c–l) compared to the levels observed after GFP overexpression in primary astrocytes, further supporting the idea that TDP-43 overexpression induced inflammation in primary astrocytes
(See figure on previous page.) Fig. 1 Expression levels of Protein tyrosine phosphatase 1B (PTP1B) and proinflammatory genes are upregulated primary astrocytes by TDP-43 overexpression in a, b, astrocytes were transfected with a GFP or TDP-43-GFP expression construct, and after 3 days, FACS of Gfp-transfected live cells was performed. a Successful transfection of Gfp- or TDP-43-Gfp in cells was confirmed by immunoblotting using an anti-TDP-43 or anti-GFP antibody
Summary
Cytoplasmic inclusions of transactive response DNA binding protein of 43 kDa (TDP-43) in neurons and astrocytes are a feature of some neurodegenerative diseases, such as frontotemporal lobar degeneration with TDP-43 (FTLD-TDP) and amyotrophic lateral sclerosis (ALS). Cytoplasmic aggregation of TDP-43 is one of the major features in TDP-43 proteinopathy [1, 11, 12], and these aggregates are associated with many neurodegenerative diseases, including FTLD, ALS and Alzheimer’s disease (AD) [3, 13, 14]. This cytoplasmic accumulation of TDP-43 eventually leads to neuronal toxicity. These data suggest that nonneuronal cells, such as microglia and astrocytes, contribute to neuronal toxicity in TDP-43 proteinopathy
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