Endogenous Elevations of Short Chain Fatty Acids Up-Regulate Embryonic Globin Gene Expression during Primitive Erythropoiesis.

We examined the effects of short chain fatty acids (SCFAs) on globin gene expression during development. We studied globin gene expression in transgenic mice that have endogenous elevations in the SCFA propionate due to a knockout (KO) of the gene for propionyl CoA carboxylase subunit A (PCCA, Miyazaki et al. JBC, 2001 Sep 21;276(38):35995–9). Serum propionate levels measured by gas chromatography were 2.5 to 3.6 mgms/ml in 2 adult PCCA KO mice and were undetectable in 2 wild type (wt) or heterozygous control adult mice. Embryonic PCCA KO offspring had propionate levels of 2.3 and 5.0 μgms/100 mgms of fetal liver, at day 16.5 (E16.5), while wt or heterozygotes at E14.5 had levels <1 μgm/100 mgms. Analysis of expression from alpha (α), beta major (β^maj), embryonic beta-type epsilon-y (ε^y), embryonic beta-type beta H1 (β^H1) and embryonic alpha-type zeta (ζ) globin genes plus 18S ribosomal RNA as a control was undertaken using real-time PCR with gene-specific primers and taqman probes. cDNA was reverse-transcribed from the mRNA of yolk sac (YS) and fetal liver of PCCA KO and wt progeny of more than one litter from timed pregnancies. Individual PCCA embryos at E10 (n=10), E12 (n=9), and E14 (n=7) were analyzed for globin gene expression, normalized to18S expression and were compared to age-matched wt embryos (n>=4 for each time point). As expected, embryonic alpha- and beta-type globin gene expression (ζ and β^H1 plus ε^y) predominated in E 10 YS, and definitive globin gene expression, α and β^maj, predominated in E12 or E14 fetal liver. Expression from embryonic alpha-type globin was calculated as normalized ζ/(ζ+α) and from embryonic beta-type globins as normalized (β^H1+ε^y)/(β^H1+ε^y+β^maj), see table. Embryonic globin gene expression was statistically significantly increased in PCCA KO E12 YS at 1.3 fold relative to wt ζ and in PCCA KO E14 YS at 1.8 fold and 2.1 fold relative to wt ζ or β^H1 and ε^y respectively (p<.05). No increase in embryonic globin mRNA was seen in adult PCCA KO animals. We conclude that elevations of SCFAs during normal murine development causes a persistence of both embryonic alpha-type and embryonic beta-type globin gene expression during primitive, but not definitive, erythropoiesis, suggesting that SCFAs cannot reactivate silenced murine embryonic globin genes in the absence of erythroid stress.

Embryonic Globin Gene Expression in Mice with Endogenous Elevations of SCFAs