How a single protein disrupts muscle and brain communication with age

Sarcopenia is a prevalent age-related disorder characterized by progressive muscle atrophy. Impaired balance is one of its most critical clinical consequences, often leading to falling and even bone fractures. As the cerebellum plays a central role in regulating motor coordination, elucidating the molecular mechanisms underlying imbalance in sarcopenia, particularly those mediated by the muscle-cerebellum axis, remains an important yet unresolved question. 4D label-free proteomics was employed to identify the key secretory protein mediating the interaction between muscles and cerebellums in young and aged mice. Annexin A2 (ANXA2), the candidate protein, was subsequently overexpressed using adeno-associated virus (AAV), and its effects on both muscle and cerebellum were systematically examined. RNA-sequencing was conducted to elucidate the molecular mechanisms underlying ANXA2 function in muscle, while stereotactic injection was performed to investigate its impact on cerebellum and related mechanisms. Finally, we evaluated the therapeutic potential of isoliquiritigenin, an inhibitor of ANXA2, in improving motor coordination and muscle function in aged mice. Aged mice showed obviously impaired motor coordination in the accelerated rotarod (AR) test (p < 0.01) and reduced strength performance in the grip strength assay (p < 0.05) compared to young mice. Proteomic analysis identified ANXA2 as a secretory protein predominantly produced by aged skeletal muscles (p < 0.05 in tibialis anterior, gastrocnemius muscle and quadriceps femoris) but not by other aged organs such as heart, liver, kidney, spleen and lung (all p > 0.05). Functionally, ANXA2 exacerbated muscle atrophy by upregulating atrophy-related markers MuRF-1 and Atrogin-1 (both p < 0.05) and reducing the myotube diameter via regulation of Neuraminidase 2 (Neu2) (p < 0.05). Moreover, ANXA2 was transported into the cerebellum through the blood stream and targeted type 2 cannabinoid receptors (CB2R) in cerebellar Purkinje cells (PCs) of lobule IV/V, thereby contributing to motor incoordination as evidenced by impaired performance in AR tests (p < 0.05). Importantly, isoliquiritigenin, an extract from licorice, effectively inhibited ANXA2 expression in muscle (p < 0.05), alleviated muscle atrophy (p < 0.05) and motor incoordination (p < 0.05), while showing no adverse effects on anxiety-like behaviours associated with CB2R (p > 0.05). ANXA2 is a key mediator of the muscle-cerebellum axis in sarcopenia, contributing to muscle atrophy by downregulating Neu2 and motor incoordination by targeting CB2R. Isoliquiritigenin was identified as an effective compound targeting ANXA2 to improve motor deficits. These findings highlight ANXA2 as a potential therapeutic target and suggest isoliquiritigenin as a promising strategy for alleviating motor incoordination associated with sarcopenia.