Background/Purpose: HRES-1/Rab4 or Rab4A, a GTPase responsible for mitochondrial oxidative stress¹ and activation of the mechanistic target of rapamycin², is overexpressed in T cells of systemic lupus erythematosus (SLE) patients³ and livers of lupus-prone mice⁴. Therefore, we investigated the impact of Rab4A on hepatitis in spontaneous and pristane-induced mouse models of SLE.

Methods: C57Bl/6J wild-type (B6) mice, strains expressing constitutively active Rab4A (Rab4A^Q72L) in all cells, and strains lacking Rab4A in T cells (Rab4A^CD4-KO) were injected intraperitoneally (ip) with pristane (500µL/20g body weight). Rab4A^Q72L­­ and Rab4A^CD4-KO mice were generated on both B6 and lupus prone SLE1.2.3 B6-triple congenic backgrounds (B6.TC). Rapamycin was administered to 27-week-old B6.TC mice (ip) 3 times weekly at a concentration of 3 µg/g for 14 weeks. The number of inflammatory cells, inflammatory foci, cells/foci, and vasculitic lesions were used to measure inflammation normalized to surface area within mouse livers. Vasculitis was scored as earlier described⁵. Student’s t-test was used to test significance; 2-tailed p values < 0.05 were considered significant for hypothesis testing

Results: Following pristane injection, B6/Rab4A^CD4-KO mice had fewer inflammatory foci/mm² (0.32±0.10 vs 1.62±0.45; p=0.042) and vasculitic lesions (0.22±0.02 vs 1.60±0.46; p=0.033) than WT controls. The average vasculitis score was decreased in B6 Rab4A^CD4-KO animals (2±0.324) compared to B6 (3.1±0.11; p=0.0016) and B6 Rab4A^Q72L controls (2.9±0.18; p=0.014). Female lupus prone B6.TC mice had more inflammatory foci/mm² (3.04±0.2) than B6 controls (0.93±0.15; p=0.0052). Male B6.TC mice did not show differences in liver inflammation relative to B6 controls. Rapamycin reduced the number of inflammatory and vasculitic foci irrespective of genetically enforced changes in expression of Rab4A. Among female B6.TC mice, 30-50 weeks of age, rapamycin-treated B6.TC Rab4A^CD4-KO had fewer inflammatory cells/mm² (0.41±0.039) compared to rapamycin-treated B6.TC mice (19.10±6.14; p=0.038) and rapamycin-treated B6.TC Rab4A^Q72L mice (4.52±1.21; p=0.020). Vehicle treated B6.TC Rab4A^CD4-KO also had less severe vasculitis (1.58±0.16) compared to vehicle treated B6.TC Rab4A^Q72L (2.67±0.56; p=0.014). Vehicle treated B6.TC Rab4A^Q72L had more severe vasculitis (2.67±0.56) compared to vehicle treated B6.TC mice (1.75±0.14; p=0.047). Among 20-40-week-old females, B6 Rab4A^CD4-KO mice had fewer inflammatory foci/mm² (8.36±2.66) compared to B6 Rab4A^Q72L mice (29.56±7.87; p=0.043). B6.TC/Rab4A^Q72L mice had moderately increased vasculitis severity (2.019±0.10) compared to B6.TC mice (1.82±0.094; p=0.151). By contrast, vasculitis was reduced in B6.TC/Rab4A^CD4-KO mice (1.71±0.075) relative to B6.TC/Rab4A^Q72L mice (2.02±0.10; p=0.0428).

Conclusion: Activation of Rab4A predisposes while its T cell-specific deletion protects against inflammation and vasculitis in the livers of mice with spontaneous or pristane-induced SLE. mTOR blockade with rapamycin reduced hepatitis in lupus prone mice.

Table summary of Rab4 effect on Pristane-induced SLE liver disease.

Table summary of liver disease in the following genotypes: Female SLE1.2.3. vs. female C57Bl/6J; Male SLE1.2.3. vs. male C57Bl/6J; Vehicle/NAC/Rapamycin effects on female SLE1.2.3. mice (30-50 weeks of age) with differential Rab4A expression (Wild Type, Q72L, CD4KO).

Table summary of liver disease in the following genotypes: Female SLE1.2.3. mice (20-40 weeks of age) with differential Rab4A expression (Wild Type, Q72L, CD4KO).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/rab4a-activation-predisposes-to-hepatitis-in-spontaneous-and-pristane-induced-mouse-models-of-systemic-lupus-erythematosus/