Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology. The pathogenesis is at least partly attributed to T-cell dysfunction. Therefore, the proposed studies will focus on a critical gap in knowledge - how autophagy pathways that regulate normal T-cell development cause pro-inflammatory population skewing and dysfunction in SLE. The central hypothesis of this project has been based on recent evidence for the contribution of endosomes to the formation of autophagosomes and the role of Rab4A in increased autophagy in lupus T cells. Rab4A is a small GTPase that regulates endosome recycling. It is markedly overexpressed in SLE patients and, even prior to disease onset, in lupus-prone mice. Although autophagy genes, in particular ATG5, have been genetically linked to SLE, their role in pathogenesis is undefined. Notably, ATG5 is transported by CD71+ endosomes which are recycled by Rab4A. Newly developed mice carrying constitutively active Rab4AQ72L show increased expression of CD71 and depletion of ATG5. Splenocytes and thymocytes of these mice show activation of mTORC1 and depletion of FoxP3. While mTORC1 is generally regarded as an inhibitor of autophagy, it is activated on the surface of lysosomes. Thus, based on compelling preliminary data, the Specific Aims will test the working hypothesis that Rab4A overexpression is responsible for accelerated autophagy and, through promoting the traffic of mTORC1 to lysosomes, for abnormal T-cell development in SLE. Given that the GTPase inhibitor 3-PEHPC inactivates Rab4A in vitro and blocks lupus pathogenesis in vivo, the proposed experiments will determine whether 1) Rab4A promotes CD71/ATG5-dependent autophagosome formation in SLE patients; 2) mTORC1 activation and FoxP3 depletion occur through endocytic traffic to lysosomes; and 3) inactivation of Rab4A blocks pathogenesis in lupus-prone mice.
Under Aim 1, Rab4A overexpression will be assessed in longitudinal studies of SLE patients as the cause of enhanced autophagosome biogenesis via the retention of CD71.
Under Aim 2, Rab4A-initiated traffic of mTOR from inhibitory Rab5+ endosomes to Rheb+ lysosomes will be evaluated as the mechanism underlying mTORC1 activation and the resultant Treg?Th17 trans-differentiation in SLE patients.
Under Aim 3, the role of Rab4A-driven autophagy in lupus will be modeled by the impact of constitutively active Rab4AQ72L on development of autoimmunity and the dependence of pathogenesis on Rab4A, ATG5 and ATG7 and downstream activation of mTORC1 and inhibition of mTORC2. The proposed research is significant because it will advance our basic understanding of autophagosome biogenesis and its impact on T-cell development and plasticity with broad translational relevance for the pathogenesis and treatment of lupus. The approach is innovative as it will employ genetically defined checkpoints of endosomal traffic to influence lupus pathogenesis. The results will bring new perspectives to our understanding of endosome traffic, how it controls autophagosome formation and its role in disease pathogenesis, and will identify new mechanistic targets for treatment of SLE.
This project is focused on the pathogenesis of systemic lupus erythematosus (SLE), a chronic autoimmune disease of unknown etiology. The proposed research is relevant to public health as SLE affects 0.1% of the US population, mainly women of child-bearing age, with 10% mortality in 5 to 10 years. There is an unmet medical need as current treatments are only partially effective and carry significant side effects. Development of new therapies has been hampered by gaps in our understanding of pathogenesis. Autophagy, a protein degradation pathway, has recently emerged as an essential regulator of immune responses and a contributor to lupus pathogenesis. This pathway depends on the formation of a special organelle, the autophagosome that carries cargo to the site of degradation, which is the lysosome. Both the formation of the autophagosome and its traffic to the lysosome involves the recycling endosome. Preliminary results indicate that lupus T cells exhibit lysosomal accumulation and increased spontaneous autophagy that are secondary to the overexpression of the endosomal small GTPase Rab4A both in SLE patients and, prior to disease onset, in lupus-prone mice. Given that inhibition of this GTPase blocks nephritis in lupus-prone mice, the proposed experiments will determine its role disease pathogenesis during longitudinal studies of SLE patients and lupus-prone mice. This project will result in new, fundamental knowledge of autophagy pathways that control immune responses and autoimmunity. The expected discoveries will be relevant for elucidating the pathogenesis and finding new targets for treatment in SLE.
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