Effect of Rapamycin on Endothelial Function in Systemic Lupus Erythematosus (SLE)
Authors: Kim Hyoseon , Massett Michael P. 
Published: May 2024

Mitophagy is regulated by multiple molecular pathways, including the mechanistic target of rapamycin (mTOR), which inhibits mitophagy. Elevated activation of mTOR complex 1 (mTORC1) is reported in humans and mice with SLE, suggesting that impaired mitophagy may contribute to the pathogenesis of SLE. As previously studied in genetically modified mice, mTORC1 also is proposed to be a critical regulator of endothelial function. However, it is unclear if pathologically elevated mTORC1, as in SLE, causes impaired mitophagy and endothelial dysfunction. Therefore, the study aimed to determine the effect of inhibition of mTORC1 on mitophagy, endothelial function, and inflammatory responses in SLE. We hypothesize that inhibiting mTORC1 with rapamycin will increase mitophagy and attenuate endothelial dysfunction and inflammatory responses in SLE. Nine-week-old female lupus-prone (MRL/lpr) and healthy control (MRL/MpJ) mice were randomly assigned into one of two groups, rapamycin treatment (lpr_Rapa and MpJ_Rapa) or control (lpr_Con and MpJ_Con). Rapamycin was injected i.p. three days a week for 8 weeks. After 8 weeks of treatment, endothelium-dependent vasorelaxation to acetylcholine (Ach) and endothelium-independent vasorelaxation to sodium nitroprusside (SNP) were measured in thoracic aortas using a wire myograph. Maximal responses to Ach were significantly impaired in lpr_Con (51.7 ± 6.6%, n = 11) compared to MpJ_Con (86.7 ± 3.6%, n = 11) (p < 0.0001). Rapamycin prevented endothelial dysfunction in the thoracic aorta from lupus mice (lpr_Rapa) (79.6 ± 4.2%, n = 10) compared to lpr_Con (p = 0.002). Maximal responses to SNP were not significantly different across the groups. Thoracic aortas were used to measure the content of mitophagy, inflammation, and endothelial function related proteins (n = 4-6/group). We assessed markers downstream of mTORC1 to confirm the inhibition of the mTORC1 activity. As expected, inhibition of mTORC1 activity decreased the phosphorylation of s6rp (p-s6rp/s6rp) in lpr_Rapa (0.39 ± 0.07) compared to lpr_Con (1.47 ± 0.16) (p < 0.0001). Phosphorylation of endothelial nitric oxide synthase (p-eNOS/eNOS) was 42% lower in lpr_Con (0.69 ± 0.14) than MpJ_Con (1.00 ± 0.12). Phosphorylated eNOS was 46% higher in lpr_Rapa (1.28 ± 0.15) than lpr_Con. Vascular cell adhesion protein 1 (Vcam 1), is an indicator of inflammation and is associated with atherosclerosis susceptibility. Protein content of Vcam 1 was significantly higher in lpr_Con (1.36 ± 0.06) compared to MpJ_Con (1.00 ± 0.01) (p = 0.001). The protein content of LC3II was measured as a marker of mitophagy. Though it was not significant, LC3II level was 2-fold higher in lpr_Con (2.12 ± 1.13) compared to MpJ_Con (1.00 ± 0.17), which may imply the accumulation of autophagosome resulted from inhibition of autophagic degradation. Collectively, these results demonstrate the beneficial effects of inhibiting mTORC1 on endothelial function in SLE mice and suggest inflammation and altered mitophagy contributing to endothelial dysfunction in SLE. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.