INSL6 (insulin-like 6) is a secreted peptide hormone belonging to the insulin/relaxin superfamily with primary roles in male reproductive physiology and tissue protection. INSL6 is predominantly expressed in meiotic and postmeiotic germ cells of the testis, specifically in spermatocytes and round spermatids 1. The protein is synthesized as a ~28 kDa precursor and undergoes posttranslational processing by furin protease and other mechanisms to generate an ~8 kDa mature form, with modifications including disulfide bonds, glycosylation, and ubiquitination 2. Mechanistically, INSL6 is essential for spermatogenesis progression; INSL6-deficient mice exhibit impaired fertility with arrested germ cell development at late meiotic prophase, reduced sperm motility, and increased germ cell apoptosis 3. Beyond reproduction, INSL6 functions as an injury-induced myokine with immunomodulatory properties—muscle-specific overexpression protects against autoimmune myositis through reduced lymphocyte infiltration and inflammatory cytokine expression 4. INSL6 also exhibits cardioprotective effects; genetic loss-of-function increases cardiac dysfunction and fibrosis in heart failure models, while recombinant INSL6 administration attenuates fibrosis and systolic dysfunction 5. Clinically, INSL6 expression is reduced in dermatomyositis and polymyositis patients and may serve as a prognostic biomarker in breast cancer 6. These findings suggest INSL6 has therapeutic potential for reproductive, autoimmune, and cardiovascular disorders.