KLK15 and obesity due to melanocortin 4 receptor deficiency: In summary, Lactiplantibacillus plantarum Ln4 exhibits strain-specific anti-obesity effects by: (1) suppressing adipogenesis and lipogenesis (PPARγ/SREBP1c axis), (2) enhancing fatty acid β-oxidation (PPARα/CPT1/ACO pathway), and (3) improving metabolic hormone balance and AMPK-mediated energy homeostasis.