Abnormal regulation of membrane-less organelles contributes to profilin1-associated ALS.

Profilin 1 (PFN1) is a key cytoskeletal protein that regulates actin dynamics by incorporating monomeric actin into linear filaments. PFN1 deletion or mutations have been linked to numerous neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). However, the contribution of PFN1 to neurodegenerative pathologies is poorly understood. Recent studies have implicated the role of aberrant cellular membrane-less organelles (MLOs) in neurodegenerative pathogenesis. Here, we demonstrate that PFN1 is involved in the assembly of MLOs, including Cajal bodies and Stress granules. Specifically, depletion of PFN1 leads to abnormal Cajal body accumulation and accelerated maturation into a gel-like state, consequently dysregulating snRNP biogenesis and impairing pre-mRNA splicing efficiency in both neuronal and non-neuronal cells. Similarly, we show that PFN1 knockdown accelerates the assembly of Stress granules in stressed cells. Furthermore, we demonstrate that the ALS-linked PFN1-C71 G mutant exhibits a loss of function in the context of MLO biogenesis. We further reveal that the PFN1 deficiency-induced Cajal body dysregulation, but not Stress granule assembly, is caused by cellular actin filament depolymerization. Importantly, the actin filament agonist CN04 rescues Cajal body properties in PFN1-depleted cells. Taken together, our findings shed light on the role of PFN1 in MLO biogenesis and suggest its involvement in neurodegenerative pathogenesis.