Hspa5 Deficiency Blocks Intestinal Enterocyte Differentiation in Graft-Versus-Host Disease
Authors: Gao Fei , Wu Hengwei , Jin Xin , Shi Jimin , Luo Yi , Zhao Yanmin , Huang He 
Published: December 2023

Background: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been established as an effective therapy for hematological malignancies. Graft-versus-host disease (GVHD) is a life-threatening complication, and the intestine is one of the major sites affected. Currently, immunosuppressive agents remain the preferred choice for GVHD treatment. However, treatment resistance still occurs in a large population, indicating that some tissue damage may be irreversible.

Methods: The murine transplant and GVHD model were established as previously described. To characterize the intestinal damage mediated by radiation and GVHD, murine small intestine tissues were collected at day 14 after transplantation. Primary small intestinal crypts were isolated from each group and cultured for five consecutive days to evaluate their ability to proliferate and differentiate. Single-Cell analysis was performed to characterize the impaired intestinal repair after injury.

Results: At day 14, the villus-to-crypt ratio was partially recovered in the BM group, but remained imbalanced in the GVHD group. We observed a significant decrease in the expression of Reg1, a gene expressed by enterocytes (EC), in the GVHD groups compared to the BM group. we further utilized a 3D organoid model to investigate intestinal growth and differentiation. The organoid size from the GVHD group was comparable to the BM and control groups. However, the number of buds per organoid was significantly reduced in the GVHD group compared to the BM and control groups. Immunofluorescence staining confirmed that cells in GVHD-derived organoids exhibited high proliferation (stained by Mki67) but impaired differentiation of enterocyte (stained by Aldob).

To gain insights into the cellular mechanisms influencing enterocyte differentiation, we dissociated murine small intestinal tissues from each group into single cells and sequenced them using the 10X Genomics platform. Through pseudochronological analysis, each cell was ordered along the predicted lineages and assigned a pseudotime. We found that enterocytes in GVHD exhibited a long and discontinuous trajectory, suggesting explicit blockage of EC differentiation. Functional enrichment analysis showed that pathways related to cell growth and differentiation, such as MAPK, ERBB, and inositol phosphate metabolism, were highly enriched in M2 of the control and BM groups. In contrast, MAPK was dramatically downregulated at the early stage of ISC differentiation in the GVHD group.

Next, we analyzed the differentially expressed genes in EP between the GVHD and BM groups. Endoplasmic reticulum (ER) chaperone-related genes from the heat shock protein (Hsp) 70 family (Hspa1a/1b/5), Hsp90 family (Hsp90aa1/ab1), and Hsp40 family (Dnajb1) were significantly decreased in GVHD compared to BM. Notably, Hspa5 (also known as GRP78 or Bip), which serves as a sensor of glucose levels and misfolded proteins, exhibited reduced protein levels, along with decreased IRE1ɑ phosphorylation (p-IRE1ɑ) and Xbp1s, as well as decreased PERK phosphorylation (p-PERK) and ATF6 expression.

To validate our conjecture, we utilized small intestinal organoids cultured for 3 days for further experimentation. RT-qPCR demonstrated that energy restriction downregulated the mRNA expression of Hspa5 and other chaperones. Furthermore, we treated intestinal organoids with HA15, a BIP inhibitor, which resulted in significantly enlarged area but fewer buds. Consistent with our previous findings, Hspa5 was downregulated in the HA15-treated group, along with decreased expression of Hsp family and enterocyte markers.

Since Hsp family plays key roles in restoring cellular homeostasis, we wondered if upregulating Hspa5 could protect intestinal cells from outside stimuli such as pro-inflammatory cytokines. When intestinal organoids were cocultured with IFN-g, we found that Bix, the selective Bip inducer, protected organoids from apoptosis by increasing Hsp70 expression.

Conclusion: Given that immunosuppression partly resolves GVHD, strategies aimed at restoring intestinal homeostasis should be given sufficient attention. Our study reveals that intestinal enterocyte differentiation is blocked in GVHD, possibly due to starvation and energy restriction. Deficiency in Hspa5 results in impaired intestinal repair, and increasing Hsp levels may enhance cell resistance to cytokine storms.