BHLHE41 is a basic helix-loop-helix transcriptional repressor with diverse roles in physiological processes and disease. Its primary function involves circadian rhythm regulation, where it acts as the negative limb of an autoregulatory feedback loop distinct from the PER/CRY loop 1. The protein functions by competing with CLOCK-BMAL1 heterodimers for E-box element binding in target gene promoters, thereby repressing clock gene expression 1. BHLHE41 also regulates tissue-specific processes including myogenesis, adipogenesis, and macrophage function 2. In pathological contexts, BHLHE41 demonstrates context-dependent roles. In colorectal cancer, METTL3-mediated m6A modification promotes BHLHE41 expression, which subsequently induces CXCL1 transcription to enhance immunosuppressive myeloid-derived suppressor cell migration 3. Conversely, in breast cancer, BHLHE41 acts as a tumor suppressor by inhibiting cell invasion through suppression of the MAPK/JNK signaling pathway and epithelial-mesenchymal transition markers 4. In neurodegeneration, BHLHE40/41 regulate microglial responses in lipid-rich tissues, with their loss increasing cholesterol clearance and lysosomal processing capacity 5. Additionally, O-GlcNAcylation of upstream circadian proteins can induce BHLHE41 expression, contributing to diabetes-associated cognitive impairment 1.