Current statistics indicate that approximately 10–13% of PD cases can be directly attributed to genetic mutations, while the remaining ~90% are classified as sporadic, arising from a complex interplay of environmental influences and inherent biological susceptibilities. Among the genetic contributors, mutations in the LRRK2 gene, encoding the multidomain scaffolding protein leucine‑rich repeat kinase 2, represent the most common hereditary cause of synucleinopathy. The G2019S variant is particularly notable, as it enhances LRRK2 kinase activity and disrupts endo‑lysosomal and mitochondrial function, ultimately impairing alpha synuclein clearance. Individuals carrying this mutation typically present with late‑onset autosomal dominant Parkinsonism.

To investigate how LRRK2 G2019S affects astrocytic handling of alpha synuclein, the authors isolated primary astrocytes from LRRK2 G2019S knock‑in mice and wild‑type (WT) controls. As an initial validation of their model, they introduced StressMarq’s Mouse Alpha Synuclein Pre‑formed Fibrils (catalog #SPR‑324) to assess fibril uptake. The fibrils were conjugated to a pHrodo fluorescent dye, which increases in brightness upon interaction with acidic environments, facilitating real-time visualization and quantification of fibril internalization through endo‑lysosomal pathways.

Astrocytes derived from LRRK2 G2019S mice internalized significantly fewer alpha synuclein fibrils compared to WT astrocytes. Moreover, this observation aligns with previous reports demonstrating impaired alpha synuclein clearance in the presence of the G2019S mutation. The reduced uptake suggests compromised astrocytic degradative capacity, which may elevate extracellular alpha synuclein burden and enhance the propagation of pathogenic seeds between neurons.

In contrast, analyses of LRRK2 knock‑out mouse tissue revealed the opposite phenotype: confocal imaging of stained brain sections, along with immunoblotting of astrocyte lysates, revealed reduced Clu levels when compared with WT samples. These findings support a model in which clusterin abundance is regulated downstream of LRRK2 in a genotype‑dependent manner. Furthermore, the significance of this relationship is amplified when considered alongside previous work demonstrating that clusterin binds alpha synuclein fibrils and restricts their internalization by astrocytes. Taken together, this evidence suggests that altered Clu levels in LRRK2 mutant astrocytes may directly contribute to the impaired fibril uptake observed in the G2019S model.

With the goal of identifying potential post‑transcriptional regulators of clusterin, the authors screened online databases for microRNAs (miRNAs) predicted to target Clu mRNA. Expression profiling in primary astrocytes highlighted miR‑22‑5p as the most consistently genotype‑responsive candidate. Indeed, miR‑22‑5p levels were elevated in LRRK2 knock‑out astrocytes but reduced in LRRK2 G2019S astrocytes relative to WT. A luciferase reporter assay confirmed direct binding between Clu mRNA and a miR‑22‑5p mimic, validating miR‑22‑5p as a bona fide translational regulator of clusterin.

miR‑22‑5p as a regulator of alpha synuclein uptake

Functionally, overexpression of the miR‑22‑5p mimic in primary astrocytes reduced both preClu and cleaved clusterin protein levels without decreasing Clu mRNA abundance, consistent with translational repression. Crucially, restoring miR‑22‑5p levels in LRRK2 G2019S astrocytes increased their uptake of pHrodo‑labeled alpha synuclein fibrils. This was reflected by a rightward shift in cumulative intracellular fluorescence compared to untreated controls, indicating enhanced fibril internalization.

Together, these data support a mechanistic model in which dysregulated miR‑22‑5p contributes to elevated clusterin levels in LRRK2 G2019S astrocytes, thereby limiting their capacity to internalize alpha synuclein fibrils. Normalizing miR‑22‑5p expression reverses this effect by lowering clusterin abundance and improving astrocytic clearance of extracellular fibrils, linking miRNA‑mediated translational control directly to glial processing of pathogenic alpha synuclein seeds.

Taken together, the study positions the LRRK2-clusterin axis as a promising therapeutic target for enhancing astrocytic clearance of alpha synuclein. Modulating miR‑22‑5p or directly targeting clusterin could potentially normalize uptake mechanisms in individuals carrying PD‑associated LRRK2 mutations. Future work assessing the impact of LRRK2 kinase inhibitors, miRNA‑based therapeutics, or other approaches that modulate this pathway will be crucial in determining whether these strategies can reduce the spread of alpha synuclein pathology and ultimately alter disease progression.