Cannabidiol activates autophagy and promotes tau clearance

A study published in the scientific journal Neurotoxicity Research, first-authored by pharmacist and current Medical Science Liaison (MSL) at CR Wellness, Talita A. M. Vrechi—which stemmed from her doctoral research at the Escola Paulista de Medicina of the Universidade Federal de São Paulo (Unifesp)—indicates that cannabidiol (CBD) can activate autophagy and promote the degradation of the tau protein in a cellular model of tauopathy.

Conducted by researchers affiliated with the Universidade Federal de São Paulo (Unifesp), Universidade de São Paulo (USP), and University College London, the study utilized a human neuroblastoma cell line modified to produce elevated levels of tau.

The findings are preclinical and contribute to the understanding of the cellular mechanisms through which cannabinoids may act on processes related to neurodegeneration. The scientific paper was published in February 2025.

Tau accumulation is associated with tauopathies

Tau is a phosphoprotein predominantly found in the central nervous system. Under physiological conditions, it participates in the organization and stability of microtubules—structures responsible for cellular support and the transport of components within neurons.

When hyperphosphorylated, tau can detach from microtubules, undergo conformational changes, and accumulate inside cells. This process is linked to diseases classified as tauopathies, including Alzheimer's disease, frontotemporal dementia, Pick's disease, and progressive supranuclear palsy.

The accumulation of the protein can also impair the pathways responsible for degrading cellular components, including autophagy.

Autophagy is a lysosome-dependent catabolic process. Through it, proteins, aggregates, and damaged organelles are sequestered into structures called autophagosomes and delivered for degradation. For this reason, modulating autophagy has been studied as a potential target in neurodegenerative diseases.

Cellular model produced elevated levels of tau

The researchers used SH-SY5Y cells, a human neuroblastoma line commonly employed in experimental studies of the nervous system.

The cells were engineered to express wild-type EGFP-Tau protein using a Tet-On inducible system. Tau expression was induced with doxycycline at a concentration of 1 µg/mL for 72 hours.

Following this period, the cells were exposed to CBD at concentrations of:

• 100 nanomolar;
• 250 nanomolar;
• 1 micromolar;
• 10 micromolar.

CBD exposure was maintained for 24 hours in cell viability and tau quantification assays. For the initial autophagy analyses, treatments were conducted for two hours.

The protocol included an MTT cell viability assay, western blotting, confocal microscopy, and automated fluorescence analysis.

The researchers evaluated total tau using the Tau-5 marker and two phosphorylated forms of the protein: AT8, corresponding to residues pSer202/pThr205, and AT180, related to residue pThr231.

CBD reduced the amount of total tau

Activation of the Tet-On system resulted in a 69% increase in total tau expression. Increases of 50% in the AT8 marker and 38.7% in AT180 were also observed compared to cells that did not receive doxycycline.

Treatment with CBD for 24 hours reduced the amount of total tau across all tested concentrations:

• 42% reduction at 100 nM;
• 64% reduction at 250 nM;
• 64% reduction at 1 µM;
• 50% reduction at 10 µM.

The absence of an increasing linear response indicates that higher concentrations did not necessarily produce greater protein reductions.

Effect differed across phosphorylation sites

CBD also reduced the AT8 phosphorylated form:

• 35% at 250 nM;
• 37% at 1 µM;
• 38% at 10 µM.

The differences were statistically significant. In contrast, none of the tested concentrations significantly reduced phosphorylation at the AT180 marker.

This outcome indicates a differential action on tau phosphorylation sites. CBD reduced phosphorylation at residues Ser202/Thr205, recognized by the AT8 antibody, but did not produce the same effect on residue Thr231, identified by AT180.

The researchers also analyzed cells expressing the P301L tau variant. This mutation is used experimentally to model alterations associated with tauopathies.

In this cell line, CBD at 1 µM reduced phosphorylation at the AT8 site by 30%. ACEA, a selective CB1 receptor agonist, produced a 27% reduction at the same concentration.

Treatments did not compromise cell viability

The MTT assay did not detect statistically significant changes in the viability of cells exposed to CBD.

Similarly, no significant changes were observed after treatment with ACEA or GW-405,833, selective agonists of CB1 and CB2 receptors, respectively.

This result indicates that the reduction in tau was not accompanied by a measurable loss of metabolic viability under the evaluated experimental conditions.

Markers indicated activation of autophagy

To investigate whether the tau reduction was related to autophagy, the researchers analyzed the LC3-II protein, a marker associated with autophagosome membranes.

Cells were treated with CBD in the presence and absence of a blocker of the final stage of autophagic flux. Under these conditions, CBD at 100 nM and 10 µM increased LC3-II accumulation by 135.9% and 112.4%, respectively.

The team also transfected the cells with mCherry-LC3, a tool that allows the visualization of autophagosome formation via confocal microscopy.

After two hours, the number of mCherry-LC3-positive puncta increased by:

• 96.1% with CBD at 100 nM;
• 95.4% with CBD at 10 µM;
• 96.1% in the positive control subjected to nutrient deprivation.

Taken together, the findings indicated an increase in autophagosome formation following exposure to CBD.

Autophagy inhibition reversed tau reduction

The involvement of autophagy in tau degradation was examined using pharmacological inhibitors.

CBD at 1 µM reduced EGFP-Tau fluorescence intensity by 34.8%. At a concentration of 10 µM, the reduction was 39.9%.

When cells were co-treated with chloroquine, a compound that disrupts autophagosome-lysosome fusion, the effect was reversed. Fluorescence intensity increased again, indicating tau accumulation following the blockade of the lysosomal stage.

CB1 and CB2 agonists also reduced EGFP-Tau fluorescence. However, the reversal induced by chloroquine was observed most consistently in the groups treated with CBD at 1 and 10 µM and with the CB2 agonist GW-405,833 at 2 µM.

According to the authors, these findings support the participation of autophagy in the CBD-promoted degradation of tau.

Findings point to a possible neuroprotective mechanism

The combined results demonstrate that CBD:

• reduced total tau;
• decreased phosphorylation at the AT8 epitope;
• increased LC3-II expression;
• stimulated autophagosome formation;
• reduced tau-associated fluorescence;
• partially lost this effect when lysosomal degradation was inhibited.

The study suggests, therefore, that activating autophagy may be one of the mechanisms involved in CBD's action on tau accumulation.

According to the authors, modulating this pathway may represent a relevant target for future research on cannabinoids and neurodegenerative diseases.

Findings remain at the preclinical stage

The study was conducted exclusively in laboratory-cultured cells. Patients, clinical manifestations, cognition, behavior, and the progression of neurodegenerative diseases were not evaluated.

The nanomolar and micromolar concentrations correspond to direct exposure of cells to CBD in culture media. They do not represent clinical dosages and cannot be directly converted into milligrams or prescription regimens.

Furthermore, the study does not establish any therapeutic indication, dosage, administration route, or clinical protocol for Alzheimer's disease or other tauopathies.

The results should be interpreted as mechanistic evidence that CBD can modulate autophagy and tau clearance within the cellular model used. Confirming its therapeutic potential will depend on further experimental and clinical stages.

The research

The research received funding from the Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp), while some researchers were supported by grants from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes).

The CBD used in the experiments was provided by BSPG-Pharm.