Identification of HSPB8 modulators counteracting misfolded protein accumulation in neurodegenerative diseases

Aims: The small Heat Shock Protein B8 (HSPB8) is the core component of the Chaperone-Assisted Selective Autophagy (CASA) complex. This complex selectively targets, transports, and tags misfolded proteins for their recognition by autophagy receptors and insertion into the autophagosome for clearance. CASA is essential to maintain intracellular proteostasis, especially in heart, muscle, and brain often exposed to various types of cell stresses. In neurons, HSPB8 protects against neurotoxicity caused by misfolded proteins in several models of neurodegenerative diseases; by facilitating autophagy, HSPB8 assists misfolded proteins degradation also counteracting proteasome overwhelming and inhibition.Materials and methods: To enhance HSPB8 protective activity, we screened a library of approximately 120,000 small molecules to identify compounds capable of increasing HSPB8 gene transcription, translation, or protein stability.Key findings: We found 83 active compounds active in preliminary dose-response assays and further classified them in 19 chemical classes by medicinal chemists' visual inspection. Of these 19 prototypes, 14 induced HSPB8 mRNA and protein levels in SH-SY5Y cells. Out of these 14 compounds, 3 successfully reduced the aggregation propensity of a disease-associated mutant misfolded superoxide dismutase 1 (SOD1) protein in a flow cytometrybased aggregation assay (Flow cytometric analysis of Inclusions and Trafficking (FloIT)) and induced the expression (mRNA and protein) of some autophagy receptors. Notably, the 3 hits were inactive in HSPB8depleted cells, confirming that their protective activity is mediated by and requires HSPB8.Significance: These compounds may be highly relevant for a therapeutic approach in several human disorders, including neurodegenerative diseases, in which enhancement of CASA exerts beneficial activities.

Automated summary

The study identified three compounds that can enhance the transcription and translation of HSPB8 and reduce the aggregation propensity of a disease-associated mutant SOD1 protein. These compounds play an important role in improving cellular proteostasis and enhancing selective autophagy, and may have significant clinical implications for treating neurodegenerative diseases and other human disorders.