Gaguine, C. | Search bioRxiv

bioRxiv2026

Tau isoforms modulate the axon initial segment controlling axonal trafficking and neuronal excitability

The axon initial segment (AIS) is a specialized neuronal compartment integrating action potential initiation with selective control of axonal trafficking. The microtubule associated protein tau is a central regulator of cytoskeletal organization and transport, yet how distinct tau isoforms contribute to AIS development and function remains unclear. Here, we examined the role of tau isoform relative abundance in regulating AIS establishment, maturation, excitability, and transport selectivity using murine primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons combined with super resolution imaging, electrophysiology, and live trafficking assays. We found that tau expression levels and isoform content modulate the timing and robustness of AIS maturation. In murine neurons, tau deficiency or predominance of 3 repeat (3R) tau delays Ankyrin G accumulation and AIS stabilization without preventing AIS formation. hiPSC-derived neurons display an intrinsic AIS developmental program accompanied by progressive changes in tau isoform content. Super resolution DNA PAINT reveals that endogenous tau decorates axonal microtubules in discrete nanoclusters with compartment specific distributions. Modulation of the endogenous 3R/4R tau balance in hiPSC-derived neurons shows that isoform composition, independently of tau levels, regulates AIS positioning and Ankyrin G organization. Functionally, shifts towards 3R-tau reduce sodium currents, impair action potential firing, and alter lysosomal transport dynamics within the AIS. Together, these findings identify tau isoform balance as a developmental regulator of AIS maturation, linking cytoskeletal organization to neuronal excitability and transport gating. Because the aberrant alternative tau splicing of exon 10 is a defining feature of primary tauopathies, our results provide mechanistic insight into how imbalanced tau isoforms may contribute to neuronal dysfunction.

cell biology↗

bioRxiv2025

Artificial microRNAs targeting Tau enable post-symptomatic functional recovery in aged tauopathy mice

Tauopathies are a group of neurodegenerative disorders, including Alzheimers disease, frontotemporal dementia, and progressive supranuclear palsy, characterized by the pathological accumulation of tau protein. While tau reduction has emerged as a promising disease-modifying strategy, most preclinical studies have focused on preventive approaches, and the therapeutic potential after clinical onset remains largely unexplored. This limitation is critical, as patients are typically diagnosed after symptoms emerge. Furthermore, global tau suppression may disrupt physiological tau functions and lead to adverse effects, underscoring the need for targeted interventions. RNA-based therapies, particularly microRNA (miRNA)-mediated silencing, offer high specificity, versatility, and sustained target knockdown. Here, we developed artificial microRNAs (Tau-miRNAs) designed for site-directed expression to selectively reduce tau levels in vulnerable brain regions, thereby minimizing off-target effects. We tested the efficacy of Tau-miRNAs in a tauopathy mouse model at advanced disease stages, delivering them into the prefrontal cortex after cognitive and electrophysiological deficits had developed. This post-symptomatic intervention led to long-term improvements in memory, restoration of neuronal firing properties, and reduced pathological tau at synapses. Our findings highlight the therapeutic potential of spatially targeted RNA-based tau-lowering strategies for late-stage intervention in tauopathies, addressing a critical unmet need in the treatment of these devastating disorders.

neuroscience↗