Chaperone Mediated Autophagy Degrades TDP-43 Protein and Is Affected by TDP-43 Aggregation

Abstract

TAR DNA binding protein 43 kDa (TDP-43) is a ribonuclear protein regulating many aspects of RNA metabolism. Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD) are fatal neurodegenerative diseases with the presence of TDP-43 aggregates in neuronal cells. Chaperone Mediated Autophagy (CMA) is a lysosomal degradation pathway participating in the proteostasis of several cytosolic proteins including neurodegenerative associated proteins. In addition, protein oligomers or aggregates can affect the status of CMA. In this work, we studied the relationship between CMA and the physiological and pathological forms of TDP-43. First, we found that recombinant TDP-43 was specifically degraded by rat liver's CMA+ lysosomes and that endogenous TDP-43 is localized in rat brain's CMA+ lysosomes, indicating that TDP-43 can be a CMA substrate in vivo. Next, by using a previously reported TDP-43 aggregation model, we have shown that wild-type and an aggregate-prone form of TDP-43 are detected in CMA+ lysosomes isolated from cell cultures. In addition, their protein levels increased in cells displaying CMA down-regulation, indicating that these two TDP-43 forms are CMA substrates in vitro. Finally, we observed that the aggregate-prone form of TDP-43 is able to interact with Hsc70, to co-localize with Lamp2A, and to up-regulate the levels of these molecular components of CMA. The latter was followed by an up-regulation of the CMA activity and lysosomal damage. Altogether our data shows that: (i) TDP-43 is a CMA substrate; (ii) CMA can contribute to

Molecular Chaperones: A Double-Edged Sword in Neurodegenerative Diseases

“…Inducing HSPB8 in a cell culture model increases TDP-43 turnover and overexpression of the Drosophila HSPB8 ortholog suppresses TDP-43-mediated neurotoxicity (Crippa et al, 2010 , 2016 ; Gregory et al, 2012 ). The presence of TDP-43 in the lysosomal fraction isolated from the rodent brain also indicates autophagy-mediated turnover (Ormeño et al, 2020 ). Moreover, both recombinant wildtype TDP-43 and an aggregation-prone mutant are degraded by isolated lysosomes in vitro and TDP-43 is a substrate of CMA interacting with the major CMA components in cell culture (Huang et al, 2014 ; Ormeño et al, 2020 ).…”

“…The presence of TDP-43 in the lysosomal fraction isolated from the rodent brain also indicates autophagy-mediated turnover (Ormeño et al, 2020 ). Moreover, both recombinant wildtype TDP-43 and an aggregation-prone mutant are degraded by isolated lysosomes in vitro and TDP-43 is a substrate of CMA interacting with the major CMA components in cell culture (Huang et al, 2014 ; Ormeño et al, 2020 ). Although TDP-43 aggregation upregulates CMA, it simultaneously disturbs the membrane integrity of LAMP2A-positive lysosomes compromising the autophagolysosomal pathway (Ormeño et al, 2020 ).…”

“…Moreover, both recombinant wildtype TDP-43 and an aggregation-prone mutant are degraded by isolated lysosomes in vitro and TDP-43 is a substrate of CMA interacting with the major CMA components in cell culture (Huang et al, 2014 ; Ormeño et al, 2020 ). Although TDP-43 aggregation upregulates CMA, it simultaneously disturbs the membrane integrity of LAMP2A-positive lysosomes compromising the autophagolysosomal pathway (Ormeño et al, 2020 ). It is therefore highly likely that the disruption of lysosomal membranes leads to the release of seeding-competent TDP-43 species and thus contributes to TDP-43 spreading similarly as previously shown for α-syn and Tau (Flavin et al, 2017 ).…”

Maintaining the balance of TDP-43, mitochondria, and autophagy: a promising therapeutic strategy for neurodegenerative diseases

“…Latest research shows that the chaperone-mediated autophagy (CMA) degrades TDP-43 protein and can be affected by TDP-43 aggregation [ 114 ]. The aggregated form of TDP-43 can interact with Hsc70, co-localize with Lamp2A, and upregulate the levels of these molecules to enhance CMA, a lysosomal degradation pathway [ 114 ].…”

“…Latest research shows that the chaperone-mediated autophagy (CMA) degrades TDP-43 protein and can be affected by TDP-43 aggregation [ 114 ]. The aggregated form of TDP-43 can interact with Hsc70, co-localize with Lamp2A, and upregulate the levels of these molecules to enhance CMA, a lysosomal degradation pathway [ 114 ]. It has been speculated that TDP-43 is not only a CMA substrate, but the conversion of its physiological and pathological forms is controlled by CMA, and TDP-43 polymerization affects the performance of CMA.…”