Impaired Heat Shock and Inflammatory Responses in HIKESHI-Related Leukodystrophy

HIKESHI, a critical adaptor protein, mediates the nuclear translocation of Heat-Shock Protein 70 (HSP70) under heat-shock (HS) stress. Rare recessive mutations in the HIKESHI gene result in severe neurodevelopmental disabilities, driven by impaired HS responses and cytoplasmic accumulation of HSP70. While disrupted HSP70 trafficking is well-documented, the downstream mechanisms linking these mutations to inflammation and neurodegeneration remain poorly understood.

We hypothesize that HIKESHI mutations drive severe acute inflammatory responses triggered by febrile illnesses due to disrupted HIKESHI-HSP70 interactions. To explore this, we developed induced pluripotent stem cell (iPSC) models from three families carrying HIKESHI mutations (e.g., V54L and P78S) to investigate molecular and cellular dynamics following HS.

Our results demonstrate that patient-derived iPSCs exhibit either depleted or significantly reduced HIKESHI protein levels, leading to impaired HSP70 nuclear translocation during HS. While HSP70 mRNA levels were upregulated in both control and patient cells post-HS, the upregulation was strikingly higher in-patient cells, suggesting a compensatory stress response. Immunocytochemistry revealed reduced nuclear localization of HSP70 in patient cells despite normal overall HSP70 protein levels in control.

Critically, extracellular HSP70 levels were significantly elevated in patient-derived iPSC culture media, as revealed by ELISA. This suggests that secreted HSP70 may act as a pro-inflammatory agent, triggering immune activation and amplifying cytokine-mediated inflammation.

In conclusion, our findings establish iPSCs as a robust model for HIKESHI-associated hypomyelinating leukodystrophy and uncover novel insights into the disease`s pathogenesis. The impaired nuclear localization of HSP70 and its abnormal secretion likely underpin the exaggerated HS response, heightened inflammatory signaling, and febrile illness sensitivity observed in patients. These results provide a crucial foundation for understanding HIKESHI dysfunction and its implications for neuroinflammation, offering promising avenues for therapeutic intervention targeting HSP70 dynamics and inflammation.