Unraveling the role of the IL-20 cytokine family in neurodegenerative diseases: Mechanisms and therapeutic insights.

The IL-20 cytokine family, comprising IL-19, IL-20, IL-22, IL-24, and IL-26, has emerged as a critical player in the pathogenesis of neurodegenerative diseases due to its multiple roles in inflammation, tissue repair, and immune modulation. These cytokines signal through IL-20 receptor complexes (IL-20RA/IL-20RB and IL-22RA1/IL-20RB), triggering diverse immune processes. Recent evidence highlights their significant contributions to neuroinflammation and neurodegeneration in central nervous system disorders. IL-20 family cytokines impact microglial activation, which, when dysregulated, exacerbates neuronal damage. Specifically, IL-20 and IL-24 are linked to elevated pro-inflammatory markers in glial cells, promoting neurodegeneration. In contrast, IL-22 exhibits dual functionality, exerting protective and pathological roles depending on the inflammatory milieu. Key mechanisms involve the regulation of blood-brain barrier integrity, oxidative stress, and autophagy. IL-22 and IL-24 also protect neurons by enhancing antioxidant defenses and maintaining epithelial barrier function, while their dysregulation contributes to blood-brain barrier disruption and protein aggregate accumulation, hallmark features of Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Elevated IL-22 levels in Alzheimer's disease and IL-19's regulatory role in multiple sclerosis suggest they may serve as potential biomarkers and therapeutic targets. IL-26's role in amplifying inflammatory cascades further underscores the complexity of this cytokine family in neurodegenerative pathology. Therapeutically, strategies targeting IL-20 cytokines include monoclonal antibodies, receptor modulation, and recombinant cytokine administration. These approaches aim to mitigate neuroinflammation, restore immune balance, and protect neuronal integrity. This review underscores the IL-20 family's emerging relevance in neurodegenerative diseases, highlighting its potential for novel diagnostic and therapeutic strategies.