Incomplete Inhibition of Sphingosine 1-Phosphate Lyase Modulates Immune System Function yet Prevents Early Lethality and Non-Lymphoid Lesions

BACKGROUND: S1PL is an aldehyde-lyase that irreversibly cleaves sphingosine 1-phosphate (S1P) in the terminal step of sphingolipid catabolism. Because S1P modulates a wide range of physiological processes, its concentration must be tightly regulated within both intracellular and extracellular environments. METHODOLOGY: In order to better understand the function of S1PL in this regulatory pathway, we assessed the in vivo effects of different levels of S1PL activity using knockout (KO) and humanized mouse models. PRINCIPAL FINDINGS: Our analysis showed that all S1PL-deficient genetic models in this study displayed lymphopenia, with sequestration of mature T cells in the thymus and lymph nodes. In addition to the lymphoid phenotypes, S1PL KO mice (S1PL(-/-)) also developed myeloid cell hyperplasia and significant lesions in the lung, heart, urinary tract, and bone, and had a markedly reduced life span. The humanized knock-in mice harboring one allele (S1PL(H/-)) or two alleles (S1PL(H/H)) of human S1PL expressed less than 10 and 20% of normal S1PL activity, respectively. This partial restoration of S1PL activity was sufficient to fully protect both humanized mouse lines from the lethal non-lymphoid lesions that developed in S1PL(-/-) mice, but failed to restore normal T-cell development and trafficking. Detailed analysis of T-cell compartments indicated that complete absence of S1PL affected both maturation/development and egress of mature T cells from the thymus, whereas low level S1PL activity affected T-cell egress more than differentiation. SIGNIFICANCE: These findings demonstrate that lymphocyte trafficking is particularly sensitive to variations in S1PL activity and suggest that there is a window in which partial inhibition of S1PL could produce therapeutic levels of immunosuppression without causing clinically significant S1P-related lesions in non-lymphoid target organs

Identifying sustainable pathways out of in-work poverty: Main report on the ‘Working Life in York’ survey : ESRC Knowledge Exchange Scheme ES/L002086/1

The “Identifying sustainable pathways out of in-work poverty” knowledge exchange project, centred on the design and analysis of a structured quantitative poverty survey of employees working at the three project partners (Joseph Rowntree Foundation/Housing Trust (JRF/JRHT), City of York Council (CYC) and York St John University (YSJU)) and earning (at or below) £10 per hour. The research findings from this structured quantitative poverty survey are detailed in this report. In addition the project also included a follow-up qualitative survey and an analysis of the Living Wage implementation at the three partner organisations

Histopathology of Spleen.

<p>(A) S1PL^+/+ spleen: Densely packed lymphocytes comprise the thick periarteriolar sheaths (PALS) in Wt mice. (B) S1PL^−/− spleen: There is severe depletion of T cells in the PALS. The lymphocytes in the PALS have been replaced by small numbers of macrophages, granulocytes, and plasma cells. B cell areas are still evident, with remaining lymphoid follicles and some germinal centers appearing more prominent due to lymphoid depletion of PALS. (C) S1PL^H/H spleen: The splenic white pulp contains essentially normal numbers and distributions of lymphocytes in the PALS and follicles. (D) S1PL^H/− spleen: Again, the splenic white pulp contains essentially normal numbers and distributions of lymphocytes in the PALS and follicles. H&E stain.</p

Histopathology in other tissues.

<p>(A) S1PL^+/+ heart: There is minimal interstitial tissue in Wt myocardium. (B) S1PL^−/− heart: There is a patchy to diffuse expansion of the interstitium by numerous variably-sized vacuoles and vacuolated mesenchymal cells that separate the cardiomyocytes. Scattered cardiomyocytes contain indistinct foamy inclusions and sharply demarcated clear vacuoles. (C) S1PL^+/+ urinary bladder: Normal urothelium lines the urinary bladder in Wt mice (D) S1PL^−/− urinary bladder: There is widespread ballooning vacuolization, degeneration, and apoptosis of urothelial cell. Lesions are more severe in the superficial umbrella cell layer, where degenerating cells are interspersed among vacuolated urothelial cells. (E) Bone, aged S1PL^H/− mouse: Small numbers of distended osteoclasts are present multifocally at the growth plate only. No increase in trabecular bone was evident. (F) Urinary bladder, aged S1PL^H/− mouse: Rare vacuolated urothelial cells were present in the superficial mucosa. H&E stain.</p

Human S1PL knock-in results in partial rescue of KO hematopoietic cell profile.

<p>(A) Blood cell counts were obtained from 62–75 mice of each genotype pooled from seven independent experiments giving similar results. Total thymocyte counts and fractions of SP and DN cells were determined from 3 and 15 mice of each genotype, respectively. Data are presented as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004112#pone-0004112-g002" target="_blank">Fig. 2A and B</a>; *<i>P</i><0.02, S1PL<i>^H/H vs.</i> S1PL^+/+. (B) Representative FACS plots show the CD69/CD62L Ab staining patterns of SP thymocytes from the indicated mice, identified by single expression of either the CD4 or CD8 markers. Data are presented as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004112#pone-0004112-g007" target="_blank">Fig. 7</a>. Samples from 11 additional mice of each treatment group gave similar results.</p