ABIN1 dysfunction as a genetic basis for lupus nephritis

Abstract

The genetic factors underlying the pathogenesis of lupus nephritis associated with systemic lupus erythematosus are largely unknown, although animal studies indicate that nuclear factor (NF)-κB is involved. We reported previously that a knockin mouse expressing an inactive form of ABIN1 (ABIN1[D485N]) develops lupus-like autoimmune disease and demonstrates enhanced activation of NF-κB and mitogen-activated protein kinases in immune cells after toll-like receptor stimulation. In the current study, we show that ABIN1[D485N] mice develop progressive GN similar to class III and IV lupus nephritis in humans. To investigate the clinical relevance of ABIN1 dysfunction, we genotyped five single-nucleotide polymorphisms in the gene encoding ABIN1, TNIP1, in samples from European-American, African American, Asian, Gullah, and Hispanic participants in the Large Lupus Association Study 2. Comparing cases of systemic lupus erythematosus with nephritis and cases of systemic lupus erythematosus without nephritis revealed strong associations with lupus nephritis at rs7708392 in European Americans and rs4958881 in African Americans. Comparing cases of systemic lupus erythematosus with nephritis and healthy controls revealed a stronger association at rs7708392 in European Americans but not at rs4958881 in African Americans. Our data suggest that variants in the TNIP1 gene are associated with the risk for lupus nephritis and could be mechanistically involved in disease development via aberrant regulation of NF-κB and mitogen-activated protein kinase activity.

Figure 1.

ABIN1[D485N] knockin mice develop progressive GN. (A and B) Graphical representations of the data in Table 1 showing that ABIN1[D485N] mice develop progressive glomerular and interstitial injury compared with WT mice. (C) Urine albumin-to-creatinine ratio of 3- to 4-month-old and 5- to 6-month-old ABIN1[D485N] and WT mice (total n=82). (D) Serum complement factor 3 (C3) levels for the same groups. All P values were calculated using the Mann-Whitney rank-order test.

Figure 2.

ABIN1[D485N] mouse kidneys display pathologic features of proliferative immune-mediated GN. (A) 100× magnification of a periodic acid-Schiff (PAS)–stained kidney section from a 3- to 4-month-old WT mouse. (B) Comparative 100× PAS image shows that at 3–4 months, the ABIN1[D485N] mouse kidneys display mesangial hypercellularity, matrix expansion, and capillary loop thickening compared with WT mouse kidneys. (C) 100× magnification of PAS-stained kidney section from a 5- to 6-month-old WT mouse. (D) Comparative 100× PAS image shows that at 5–6 months the ABIN1[D485N] mouse kidneys display severe mesangial hypercellularity, matrix expansion, and “wire loops” (arrow) compared with WT mouse kidneys. (E) 40× magnification PAS image showing examples of glomerular injury and extensive interstitial immune cell infiltration (arrow) observed in 5- to 6-month-old ABIN1[D485N] mouse kidneys. (F) 40× magnification of Masson trichrome staining showing examples of tubulointerstitial fibrosis, glomerular fibrosis, and crescent formation (arrow) and immune cell infiltration (lower right corner) in 5- to 6-month-old ABIN1[D485N] mouse kidneys.

Figure 3.

ABIN1[D485N] mouse glomeruli display mesangial and subendothelial deposits. (A) TEM image of WT mouse kidney (large arrow, erythrocyte; small arrow, endothelial cell). (B) Minimal mesangial expansion and immune deposits (small arrows) in a TEM image of a 4-month-old ABIN1[D485N] mouse kidney. Podocyte foot processes are intact. The large arrow points out a monocyte in a capillary. (C) Extensive mesangial expansion and immune deposits (small arrows) in a TEM image of a 6-month-old ABIN1[D485N] mouse kidney. The large arrow points out a monocyte in a capillary. (D) Example of subendothelial immune deposits (long small arrow), areas of podocyte effacement (short small arrow), and mesangial deposits (large arrow) in a 6-month-old ABIN1[D485N] mouse kidney.

Figure 4.

Deposits in ABIN1[D485N] glomeruli contain complement factors and immunoglobulins. The panels show examples of the immunofluorescence staining that was observed for the different labeled complement factors and immunoglobulin subtypes in kidneys from 5- to 6-month-old ABIN1[D485N] mice. No significant immunofluorescence was observed for same-age WT mice.

Figure 5.

Disrupted ABIN1 polyubiquitin binding contributes to the development of lupus nephritis via aberrant regulation of NF-κB and mitogen-activated protein kinase activity. Proinflammatory gene activation is mediated by NF-κB, c-JUN, and ATF2 through TLRs and IL-1R by activation of the upstream IKK complex or MAPK kinase (MKK) activation of JNK or p38 MAPK. IKK and MKKs are activated by an inflammatory activating complex consisting of IRAKs, TRAFs, RIPs, and TAK1, among others. ABIN1 binds to K63-linked and linear polyubiquitin chains and inhibits NF-κB, c-JUN, and ATF2 by interaction with these moieties on components of the inflammatory activating complex or IKKγ. Inhibition of activators of MKKs or IKK is also facilitated by ABIN1 recruitment of the de-ubiquinating protein A20. ABIN1 mutation that disrupts these inhibitory functions contributes to LN.