Regulation of Biomolecular Condensates by Poly(ADP-ribose)

Parthanatos: Mechanisms, modulation, and therapeutic prospects in neurodegenerative disease and stroke

Parthanatos is a cell death signaling pathway that has emerged as a compelling target for pharmaceutical intervention. It plays a pivotal role in the neuron loss and neuroinflammation that occurs in Parkinson's Disease (PD), Alzheimer's Disease (AD), Huntington's Disease (HD), Amyotrophic Lateral Sclerosis (ALS), and stroke. There are currently no treatments available to humans to prevent cell death in any of these diseases. This review provides an in-depth examination of the current understanding of the Parthanatos mechanism, with a particular focus on its implications in neuroinflammation and various diseases discussed herein. Furthermore, we thoroughly review potential intervention targets within the Parthanatos pathway. We dissect recent progress in inhibitory strategies, complimented by a detailed structural analysis of key Parthanatos executioners, PARP-1, AIF, and MIF, along with an assessment of their established inhibitors. We hope to introduce a new perspective on the feasibility of targeting components within the Parthanatos pathway, emphasizing its potential to bring about transformative outcomes in therapeutic interventions. By delineating therapeutic opportunities and known targets, we seek to emphasize the imperative of blocking Parthanatos as a precursor to developing disease-modifying treatments. This comprehensive exploration aims to catalyze a paradigm shift in our understanding of potential neurodegenerative disease therapeutics, advocating for the pursuit of effective interventions centered around Parthanatos inhibition.

Nuclear-import receptors as gatekeepers of pathological phase transitions in ALS/FTD

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are fatal neurodegenerative disorders on a disease spectrum that are characterized by the cytoplasmic mislocalization and aberrant phase transitions of prion-like RNA-binding proteins (RBPs). The common accumulation of TAR DNA-binding protein-43 (TDP-43), fused in sarcoma (FUS), and other nuclear RBPs in detergent-insoluble aggregates in the cytoplasm of degenerating neurons in ALS/FTD is connected to nuclear pore dysfunction and other defects in the nucleocytoplasmic transport machinery. Recent advances suggest that beyond their canonical role in the nuclear import of protein cargoes, nuclear-import receptors (NIRs) can prevent and reverse aberrant phase transitions of TDP-43, FUS, and related prion-like RBPs and restore their nuclear localization and function. Here, we showcase the NIR family and how they recognize cargo, drive nuclear import, and chaperone prion-like RBPs linked to ALS/FTD. We also discuss the promise of enhancing NIR levels and developing potentiated NIR variants as therapeutic strategies for ALS/FTD and related neurodegenerative proteinopathies.

Length-dependent Intramolecular Coil-to-Globule Transition in Poly(ADP-ribose) Induced by Cations

Poly(ADP-ribose) (PAR), as part of a post-translational modification, serves as a flexible scaffold for noncovalent protein binding. Such binding is influenced by PAR chain length through a mechanism yet to be elucidated. Structural insights have been elusive, partly due to the difficulties associated with synthesizing PAR chains of defined lengths. Here, we employ an integrated approach combining molecular dynamics (MD) simulations with small-angle X-ray scattering (SAXS) experiments, enabling us to identify highly heterogeneous ensembles of PAR conformers at two different, physiologically relevant lengths: PAR 15 and PAR 22 . Our findings reveal that numerous factors including backbone conformation, base stacking, and chain length contribute to determining the structural ensembles. We also observe length-dependent compaction of PAR upon the addition of small amounts of Mg 2+ ions, with the 22-mer exhibiting ADP-ribose bundles formed through local intramolecular coil-to-globule transitions. This study illuminates how such bundling could be instrumental in deciphering the length-dependent action of PAR.

GRAPHICAL ABSTRACT

Streptavidin-Conjugated DNA for the Boronate Affinity-Based Detection of Poly(ADP-Ribose) Polymerase-1 with Improved Sensitivity

This work reports the development of a fluorescence method for the detection of poly(ADP-ribose) polymerase-1 (PARP1), in which a phenylboronic acid-modified fluorescein isothiocyanate dye (FITC-PBA) was used to recognize the formed poly(ADP-ribose) (PAR) polymer. The detection system was designed by conjugating recombinant streptavidin (rSA) with PARP1-specific double-stranded DNA (dsDNA) through streptavidin-biotin interaction. Capture of PARP1 via rSA-biotin-dsDNA allowed for the poly-ADP-ribosylation (PARylation) of both rSA and PARP1 in a homogeneous solution. The resulting rSA-biotin-dsDNA/PAR conjugates were then captured and separated via the commercialized nitrilotriacetic acid-nickel ion-modified magnetic bead (MB-NTA-Ni) through the interaction between NTA-Ni on MB surface and oligohistidine (His₆) tag in rSA. The PAR polymer could capture the dye of FITC-PBA through the borate ester interaction between the boronic acid moiety in PBA and the cis-diol group in ribose, thus causing a decrease in fluorescence signal. The PARylation of streptavidin and the influence of steric hindrance on PARylation efficiency were confirmed using reasonable detection strategies. The method showed a wide linear range (0.01~20 U) and a low detection limit (0.01 U). This work should be valuable for the development of novel biosensors for the detection of poly(ADP-ribose) polymerases and diol-containing species.