ATF4 and osteoporosis: It achieves the treatment of osteoporosis through various pathways, including inhibiting the synthesis of gut-derived 5-HT, downregulating TPH-1 to suppress the synthesis of gut-derived 5-HT, balancing the transcription factors FOXO1, ATF4, and CREB, and regulating the gut microbiota to inhibit gut-derived 5-HT.