PTEN and intervertebral disk degenerative disorder: Previous research has shown that when MSC-derived exosomes were delivered in a rat model of IDD, NPCs were prevented from undergoing the apoptotic process and IVDD was alleviated via miR-21 contained in exosomes, as exosomal miR-21 inhibits phosphatase and tensin homolog (PTEN); therefore, activation of the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway occurred in apoptotic NPCs, and this phenomenon decreased the degree of activation level of downstream factors of Bad, Bax, and caspase-3 and ultimately hindered TNF-α mediated apoptosis [20].