15-PGDH regulates hematopoietic and gastrointestinal fitness during aging

Abstract

Emerging evidence implicates the eicosanoid molecule prostaglandin E2 (PGE2) in conferring a regenerative phenotype to multiple organ systems following tissue injury. As aging is in part characterized by loss of tissue stem cells' regenerative capacity, we tested the hypothesis that the prostaglandin-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) contributes to the diminished organ fitness of aged mice. Here we demonstrate that genetic loss of 15-PGDH (Hpgd) confers a protective effect on aging of murine hematopoietic and gastrointestinal (GI) tissues. Aged mice lacking 15-PGDH display increased hematopoietic output as assessed by peripheral blood cell counts, bone marrow and splenic stem cell compartments, and accelerated post-transplantation recovery compared to their WT counterparts. Loss of Hpgd expression also resulted in enhanced GI fitness and reduced local inflammation in response to colitis. Together these results suggest that 15-PGDH negatively regulates aged tissue regeneration, and that 15-PGDH inhibition may be a viable therapeutic strategy to ameliorate age-associated loss of organ fitness.

Fig 1. Aged PGDH KO mice display elevated PGE2.

(A-D) PGE2 levels were quantified in bone marrow (BM), spleen, lung, and colon tissue lysates obtained from 12-15-month-old FVB wildtype littermate (WT), and 15-PGDH knockout (KO) mice. N = 4 female mice/group for BM, Spleen and Lung. N = 5 mice/group for colon. (E) Figure adapted with permission from Zhang et. al (2015). PGE2 levels were quantified from 2-month-old WT and KO FVB mice. N = 5 mice/group.

Fig 2. White blood cells and HSPCs are increased in aged PGDH KO mice.

(A-C) White blood cell (WBC), neutrophil (NE), and lymphocyte (LYMPH) counts were measured in the peripheral blood of aged (19–23 months old) WT and PGDH KO mice by complete blood count analysis. N = 12 mice/group. (7 male WT/KO and 5 female WT/KO) (D-F) Fold change in the number of BM Lin^- c-Kit⁺ Sca1⁺ (LSK cells), and Lin^- c-Kit⁺ Sca1⁺ CD48^- CD150⁺ (phenotypic LT-HSCs) in aged (14–20 months old; median age: 18mos.) PGDH KO relative to WT littermates. Fold change in the number of splenic LSK cells in aged (14–20 months old; median age: 18mos.) PGDH KO relative to WT littermates. N = 6–8 mice/group, 2 independent experiments. (G, H) Figure adapted with permission from Zhang et. al (2015). Peripheral CBCs and BM HSPCs from 2-month-old WT and KO FVB mice. N = 16 mice/group for CBCs and LSK, N-13 mice/group for LT-HSC.

Fig 3. Aged 15-PGDH KO marrow shows enhanced engraftment and hematopoietic repopulation.

(A) Representative gross images of the spleen of WT recipient mice 12 days post-transplantation of aged (15 months old) WT or PGDH KO female BM. (B) Hematopoietic colony forming units on the spleen (CFU-S) were scored. N = 9 mice/group. (C) Day 12 recipient spleen weights were measured. (D) Schematic depicts the competitive transplantation of aged (14 months old) female CD45.1+ PGDH KO or WT littermate control BM with the BM of young (6 months old) CD45.2+ competitor mice. (E) Peripheral blood repopulation 8wks post-transplant was analyzed as percent CD45.1+ chimerism in peripheral blood in mice that received either WT control or PGDH KO BM. (F) BM chimerism was analyzed 20wks post-transplant as the percent CD45.1+ of total BM cells. (G) LSK chimerism was analyzed 20wks post-transplant as the percent CD45.1+ of BM LSK cells. N = 5 mice/group.

Fig 4. Crypt fitness is superior in aged PGDH KO mice.

(A) Bar graphs represent crypt heights compared between WT and PGDH KO mice at (12–34 months of age; N = 8–9 mice/group). P = 0.003 for unpaired t-test. (B-C) Representative histologic images of murine colon crypts matched at 15 months of age. H&E for WT and PGDH KO are shown. Scale bar: 200μm. (D) Positive PAB-Alcian Blue stains are quantified per unit length for mice at 12–34 months of age. N = 4 female mice/group. P = 0.008 for unpaired t-test. (E-F) Representative PAS-Alcian Blue stains performed to visualize mucin content in WT and PGDH KO distal colons matched at 23 months of age are shown.

Fig 5. Aged PGDH KO mice show less severe DSS colitis.

(A) Experimental schema for assaying DSS colitis for mice age-matched at 17–23 months of age. (B) Mouse weights relative to day one of the experiment across time are shown for WT and PGDH KO mice. Mean±SEM, N = 5 male mice/group, *P<0.05, unpaired t-test. (C) Disease activity indices (DAI) for the DSS colitis are shown for WT and PGDH KO mice. Mean±SEM, N = 5 mice/group, *P<0.05, unpaired t-test. (D) Gross colon lengths resulting from DSS exposure on day 10 are shown, Mean±SEM, N = 5 mice/group, *P = 0.01, unpaired t-test. (E) Cryptitis scores from histological analysis are shown. Mean±SEM, N = 4 mice/group. ***P = 0.001, unpaired t-test. (F) TNFα and (G) IL1β inflammatory cytokine content within the distal colons (pg/mg total protein) are quantified. P-values by unpaired t-tests. Mean±SEM, N = 5. (H) Number of goblet cells per mucosa length (mm) in the distal colon is quantified. ***P = 0.001, unpaired t-test.