Autophagy-independent cytoprotection by optineurin from toxicity of aggregates formed by mutant huntingtin and mutant ataxin-3

[Optineurin and mitochondrial dysfunction in neurodegeneration]

Optineurin (OPTN) is a multifunctional protein playing a crucial role as a receptor in selective autophagy. OPTN gene mutations are linked to diseases such as normal-tension glaucoma and amyotrophic lateral sclerosis. Recognized as a critical receptor for mitophagy, OPTN is pivotal in selectively degrading damaged mitochondria. This process is essential to prevent their accumulation, the generation of reactive oxygen species, and the release of pro-apoptotic factors. Mitophagy's quality control is governed by the PINK1 kinase and the cytosolic ubiquitin ligase Parkin, whose mutations are associated with Parkinson's disease. This review highlights recent insights emphasizing OPTN's role in mitophagy and its potential involvement in neurodegenerative diseases.

Mutant-Huntingtin Molecular Pathways Elucidate New Targets for Drug Repurposing

The spectrum of neurodegenerative diseases known today is quite extensive. The complexities of their research and treatment lie not only in their diversity. Even many years of struggle and narrowly focused research on common pathologies such as Alzheimer's, Parkinson's, and other brain diseases have not brought cures for these illnesses. What can be said about orphan diseases? In particular, Huntington's disease (HD), despite affecting a smaller part of the human population, still attracts many researchers. This disorder is known to result from a mutation in the HTT gene, but having this information still does not simplify the task of drug development and studying the mechanisms of disease progression. Nonetheless, the data accumulated over the years and their analysis provide a good basis for further research. Here, we review studies devoted to understanding the mechanisms of HD. We analyze genes and molecular pathways involved in HD pathogenesis to describe the action of repurposed drugs and try to find new therapeutic targets.

Ocular protein optineurin shows reversibility from unfolded states and exhibits chaperone-like activity

Optineurin (OPTN) is a multifunctional, ubiquitously expressed cytoplasmic protein, mutants of which are associated with primary open-angle glaucoma (POAG) and amyotrophic lateral sclerosis (ALS). The most abundant heat shock protein crystallin, known for its remarkable thermodynamic stability and chaperoning activity, allows ocular tissues to withstand stress. The presence of OPTN in ocular tissues is intriguing. Interestingly, OPTN also harbors heat shock elements in its promoter region. Sequence analysis of OPTN exhibits intrinsically disordered regions and nucleic acid binding domains. These properties hinted that OPTN might be endowed with sufficient thermodynamic stability and chaperoning activity. However, these attributes of OPTN have not yet been explored. Here, we studied these properties through thermal and chemical denaturation experiments and monitored the processes using CD, fluorimetry, differential scanning calorimetry, and dynamic light scattering. We found that upon heating, OPTN reversibly forms higher-order multimers. OPTN also displayed a chaperone-like function by reducing the thermal aggregation of bovine carbonic anhydrase. It regains its native secondary structure, RNA-binding property, and melting temperature (T _m) after refolding from a thermally as well as chemically denatured state. From our data, we conclude that OPTN, with its unique ability to revert from the stress-mediated unfolded state and its unique chaperoning function, is a valuable protein of the ocular tissues.