A single dose of engineered Klotho mRNA delivered via specialized nanoparticles restored youthful cellular function within 24 hours in aged and Klotho-deficient mesenchymal stem cells. The treatment suppressed key aging markers including p53-p21-p16 pathways, restored mitochondrial membrane potential, increased antioxidant enzyme SOD2 expression, and normalized calcium homeostasis. Remarkably, the therapy selectively targeted aged cells while leaving young cells unaffected, suggesting Klotho functions as a stress-responsive rescue factor. This selectivity is crucial for therapeutic applications, as it indicates the treatment won't disrupt normal cellular function in healthy tissue. The findings represent a significant advance in anti-aging therapeutics, offering a non-genetic approach to cellular rejuvenation through mRNA delivery. Unlike gene therapy, this approach avoids permanent genetic modification while achieving rapid results. The work builds on decades of research establishing Klotho as a longevity protein whose decline drives aging phenotypes. However, translating these promising in vitro results to human applications will require extensive safety testing and optimization of delivery systems for clinical use.