GDF11抑制mTORC1/TFEB/自噬通路促进小鼠肝脏增龄性功能衰退的作用研究

Growth differentiation factor 11 (GDF11) is a TGF-β superfamily member. The roles of GDF11 on aging and aging-related degenerative changes in organs, as well as its regulatory mechanisms remain poorly understood. In our preliminary experiments, we demonstrated that: (1)both serum and hepatic GDF11 protein expression levels were increased in aged mice; (2)GDF11 significantly promoted senescence in hepatocytes; and (3)GDF11 increased mammalian/mechanistic target of rapamycin complex 1 (mTORC1) activity, decreased transcription factor EB (TFEB) activity and impaired autophagy in hepatocytes. Prompted by these results, we hypothesized that GDF11 could inhibit mTORC1/TFEB/autophagy signaling, thus promote age-related impairments in hepatic function in mice. In the present study, we will use an in-vivo model of aged mice and an in-vitro model of primary cultured hepatocytes to demonstrate that: (1)the effect of GDF11 on promoting age-related impairments in hepatic function in mice; (2)the effect of mTORC1/TFEB signaling on GDF11-impaired autophagy; and (3)the effect of down-regulation of GDF11-restored autophagy on mitigating aging and age-related impairments in hepatic function. Finally, we will explore the effect of GDF11 on promoting aging and age-related impairments in hepatic function and its potential mechanisms in mice, and down-regulation of GDF11 may be a novel approach to the treatment of aging and age-related diseases.

GDF11是TGF-β超家族成员，其在器官衰老与器官退行性变化中的作用及分子机制，目前尚不明确。我们预实验结果表明：(1)GDF11在老年小鼠血清和肝脏中表达升高；(2)GDF11促进小鼠肝细胞衰老；(3)GDF11上调肝细胞mTORC1活性、抑制TFEB活化及下调自噬。因此，我们推断GDF11可能通过抑制mTORC1/TFEB/自噬通路，促进肝脏增龄性功能衰退。本课题拟应用自然衰老小鼠及体外培养的小鼠原代肝细胞模型，进一步探索：(1)GDF11促进小鼠肝脏增龄性功能衰退的作用；(2)给予调控mTORC1/TFEB干预，研究mTORC1/TFEB信号通路在GDF11抑制自噬中的作用；(3)下调GDF11恢复自噬在延缓老年小鼠肝脏衰老和功能衰退的作用。通过上述研究我们将阐明GDF11促进肝脏衰老和功能衰退的作用及分子机制，下调GDF11可能是有效治疗衰老和衰老相关性疾病的新途径。

GDF11是TGF-β超家族成员，其抗衰老作用尚存在争议。GDF11在肝脏衰老中的作用及分子机制，目前尚不明确。我们预实验结果表明：GDF11在老年小鼠血清和肝脏中表达升高；GDF11促进小鼠肝细胞衰老；GDF11上调肝细胞mTORC1活性、抑制TFEB活化及下调自噬。因此，我们推断GDF11可能通过抑制mTORC1/TFEB/自噬通路，促进肝脏增龄性功能衰退。在本研究中，我发现：通过注射AAV8-GDF11质粒，过表达GDF11可以显著加速老年小鼠肝脏衰老，反之，通过注射Ad-shRNA GDF11干扰质粒，下调GDF11可以显著延缓肝脏衰老；同时，过表达GDF11的老年小鼠肝脏细胞自噬流受损，反之，下调GDF11可以显著恢复老年小鼠肝脏细胞自噬流；在过表达GDF11的老年小鼠中，给予自噬激活剂(rapamycin)处理，恢复GDF11抑制的自噬，可以抵抗上调GDF11介导的促衰老作用；反之，在下调GDF11表达的老年小鼠中，给予自噬抑制剂 (bafilomycin A1)处理，抑制下调GDF11诱导的自噬，可以抵抗下调GDF11介导的抗衰老作用；GDF11可能通过抑制溶酶体生物发生，影响自噬体-溶酶体融合和/或溶酶体降解，从而抑制自噬活性；TFEB是溶酶体生物发生和自噬的重要调控因子，GDF11显著激活mTORC1，抑制TFEB活化；抑制mTORC1或过表达TFEB可以恢复GDF11对溶酶体生物发生和自噬的抑制作用及其介导的细胞衰老作用。总之，通过mTORC1/TFEB信号通路抑制自噬活性可能是GDF11加剧老年小鼠肝脏衰老的关键分子机制之一。在肝脏衰老过程中，GDF11可能不是一种抗衰老因子，而更可能是一种促衰老因子。通过上述研究我们阐明了GDF11促进肝脏衰老的作用及分子机制，下调GDF11可能是有效治疗肝脏衰老和衰老相关性疾病的新途径。