Abemaciclib partially restores blood–brain barrier integrity and P-gp function in a murine model of chronic stress

Blood–brain barrier (BBB) dysfunction, including altered permeability and efflux transporter function, is increasingly regarded as a determinant of depression pathophysiology [1]. However, the regional organization of these alterations and their relationship to behavioral changes remain poorly understood. Lately, it has been shown that β-catenin regulates key BBB components, including tight junctions and efflux transporters [2], and may link molecular and functional alterations. Here, we combined behavioral assessment, in vivo PET imaging, and molecular analyses to characterize BBB permeability and efflux function in a murine model of chronic stress. Abemaciclib, a CDK4/6 inhibitor with reported effects on signaling pathways interacting with β-catenin [3], was evaluated for its potential to modulate BBB integrity and function.

Male C57BL/6N mice (13 weeks) received corticosterone (CORT, 35 µg/L, n=13) or vehicle in drinking water for 5 weeks, followed by 6 weeks of abemaciclib (ABE, 50 mg/kg, ip., n=15) or vehicle (VEH, n=16). [¹⁸F]Fluoro-deoxy-sorbitol ([¹⁸F]FDS) was used as a PET marker of BBB permeability. The uptake rate constant of [¹⁸F]FDS (k_uptake) was estimated using graphical analysis of dynamic PET data (60 min). P-glycoprotein function was estimated from the efflux rate of the radiolabeled substrate [¹¹C]metoclopramide (k_Efflux). Western blotting of the resected brain was used to determine claudin-5 and β-catenin expression in each group. Anxiety-like behavior was assessed using the elevated plus maze.

Increased k_Efflux of [¹¹C]metoclopramide was observed in the basal forebrain/septum and brainstem of CORT mice compared to VEH (≈1.4-fold and ≈1.2-fold, respectively; p < 0.05, n=4-6) suggesting higher P-gp function. In the cerebellum, k_Efflux was higher for VEH > CORT > ABE (significantly lower than VEH, 0.6-fold, p < 0.01). The BBB permeability of [¹⁸F]FDS was higher in CORT mice compared with VEH although not significant (n=6-13). ABE significantly decreased k_uptake in CORT mice (≈0.44-fold, p=0.0149) indicating partial restoration of BBB integrity. In CORT mice compared to VEH, the expression of claudin-5 was decreased and the expression of β-catenin was increased. ABE reversed this trend and increased claudin-5 expression at a higher level than VEH (≈1.6-fold, p < 0.01). ABE decreased β-catenin expression at lower level than VEH (≈0.53-fold, p < 0.01). In the elevated plus maze, CORT mice showed reduced open-arm exploration and increased latency compared with VEH. ABE-treated mice showed intermediate behavior (p>0.05).

This study demonstrates that BBB alterations in a murine model of stress are region-specific and involve changes in permeability and efflux function. Abemaciclib partially modulated BBB parameters in a region-dependent manner. Molecular findings in claudin-5 and β-catenin support involvement of BBB regulatory pathways. Additional experiments are ongoing to assess the link between changes in BBB properties and stress-related behaviour. Overall, these in vivo results support the importance BBB regulation pathways as determinants and potential therapeutic targets for the management of chronic stress.

References

1. Welcome MO. Cellular mechanisms and molecular signaling pathways in stress-induced anxiety, depression, and blood-brain barrier inflammation and leakage. Inflammopharmacology. 2020;28(3):643-665. doi:10.1007/s10787-020-00712-8
2. Menard C, Pfau ML, Hodes GE, et al. Social stress induces neurovascular pathology promoting depression. Nat Neurosci. 2017;20(12):1752-1760. doi:10.1038/s41593-017-0010-3
3. Cousins EM, Goldfarb D, Yan F, et al. Competitive Kinase Enrichment Proteomics Reveals that Abemaciclib Inhibits GSK3β and Activates WNT Signaling. Mol Cancer Res. 2018;16(2):333-344. doi:10.1158/1541-7786.MCR-17-0468