HIV Infection Leads to Redistribution of Leaky Claudin-2 in the Intestine of Humanized SCID IL-2R −/− Hu-PBMC Mice

Gastrointestinal disease has been recognized as a major manifestation of human immunodeficiency virus (HIV) infection following the earliest knowledge of acquired immunodeficiency syndrome (AIDS). Moreover, breakdown of the intestinal mucosal barrier and resulting microbial translocation are considered to be major drivers of AIDS progression. ¹ Intestinal tight junctions (TJs) seal the space between adjacent epithelial cells, which serve as an intestinal mucosal barrier, provide structure, and play a role in host defense. Many TJ proteins (e.g., ZO-1/Occludin) are known to tighten cell structure and maintain barrier function. In contrast, Claudin-2 is a leaky protein that plays a role opposite to that of other TJ proteins. Leaky protein Claudin-2 in intestinal epithelial cells is associated with defective barriers, is elevated in the inflamed intestine, ² and may contribute to early neoplastic transformation.

Claudin-2 is increased in the HIV-infected human intestine ^3,4 and in the SIV macaque model. Previously, there have been limited small animal models for HIV. Although combined antiretroviral therapy has dramatically reduced HIV viral load, immune activation persists and is believed to drive a number of comorbid conditions associated with HIV. Increased gut permeability and microbial translocation are key processes driving persistent immune activation.

The emergence of humanized mice reconstituted with human leukocytes and infected with HIV provides a powerful tool to address HIV pathogenesis in vivo in small animals. We used the NOD SCID IL-2R^−/− Hu-PBMC mice to study HIV infection in the gut. These mice are immunocompromised and do not express the common FCγ chain, which enables their immune reconstitution with human peripheral blood mononuclear cells (Hu-PBMCs). Because it is unclear whether the humanized mouse intestine recapitulates some of the pathological features described in HIV-infected human gut, we used NOD SCID IL-2R^−/− Hu-PBMC mice to study intestinal Claudin-2 in the context of HIV infection. NOD SCID IL-2R^−/− Hu-PBMC mice were infected with HIV_Bal and 2 weeks postinfection the intestinal epithelial tissue was harvested, fixed, and assessed by immunofluorescence (IF) staining.

In the colon of uninfected mice, Claudin-2 was found at the epithelial base, and was restricted to the cell membrane (Fig. 1A). In contrast, in HIV-infected humanized mice, Claudin-2 expression was increased at the base of the crypts, and was detected in the middle and top of the crypts and along the crypt–villous axis (Fig. 1B). The distribution of Claudin-7 did not change in the mouse intestine following HIV infection (data not shown). Western blot data confirmed a significant increase of Claudlin-2 in the gut of HIV-infected humanized mice compared to uninfected controls (data not shown). Increased Claudin-2 is a hallmark indicator of disrupted and opened tight junctions. These data indicate that HIV infection alters the integrity of the intestinal epithelia. These findings model the ability of HIV infection to enhance intestinal permeability that is evident in HIV-positive patients and could elucidate previously unrecognized changes in intestinal homeostasis in the context of HIV infection.

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FIG. 1.

HIV-induced Claudin-2 in humanized mice in vivo. Immunostaining of the mouse colon was performed 2 weeks after HIV infection. Tissues were fixed, stained with Claudin-2 antibody, and further stained with a secondary antibody. HIV infection in these humanized mice not only increased Claudin-2 (green) staining at the base of the crypts but also induced Claudin-2 expression in the middle and top of the crypts.