Nominal growth hormone pulses in otherwise normal masculine plasma profiles induce intron retention of overexpressed hepatic CYP2C11 with associated nuclear splicing deficiency

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

Computational analysis of splicing errors and mutations in human transcripts

Background

Most retained introns found in human cDNAs generated by high-throughput sequencing projects seem to result from underspliced transcripts, and thus they capture intermediate steps of pre-mRNA splicing. On the other hand, mutations in splice sites cause exon skipping of the respective exon or activation of pre-existing cryptic sites. Both types of events reflect properties of the splicing mechanism.

Results

The retained introns were significantly shorter than constitutive ones, and skipped exons are shorter than exons with cryptic sites. Both donor and acceptor splice sites of retained introns were weaker than splice sites of constitutive introns. The authentic acceptor sites affected by mutations were significantly weaker in exons with activated cryptic sites than in skipped exons. The distance from a mutated splice site to the nearest equivalent site is significantly shorter in cases of activated cryptic sites compared to exon skipping events. The prevalence of retained introns within genes monotonically increased in the 5'-to-3' direction (more retained introns close to the 3'-end), consistent with the model of co-transcriptional splicing. The density of exonic splicing enhancers was higher, and the density of exonic splicing silencers lower in retained introns compared to constitutive ones and in exons with cryptic sites compared to skipped exons.

Conclusion

Thus the analysis of retained introns in human cDNA, exons skipped due to mutations in splice sites and exons with cryptic sites produced results consistent with the intron definition mechanism of splicing of short introns, co-transcriptional splicing, dependence of splicing efficiency on the splice site strength and the density of candidate exonic splicing enhancers and silencers. These results are consistent with other, recently published analyses.

Differential expression of cytochrome P450 isoforms in the lungs of septic animals

OBJECTIVE

Sepsis is characterized by an early, hyperdynamic phase and a late, hypodynamic phase. Although studies have shown that cytochrome P450 (CYP) plays an important role in the regulation of vascular reactivity, alterations of vascular CYP isoforms in sepsis remain unknown. Since CYP2C11 and CYP2J4 convert arachidonic acid to vasodilative epoxyeicosatrienoic acids, and CYP4A3 metabolizes arachidonic acid to both epoxyeicosatrienoic acids and vasoconstrictive 19,20-hydroxyeicosatetraenoic acid, the aim of this study was to examine the expression of these isoforms in sepsis and their association with hemodynamic changes.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

An institute research laboratory.

SUBJECTS

Male adult Sprague-Dawley rats were subjected either to polymicrobial sepsis by cecal ligation and puncture or to sham operation followed by the administration of normal saline solution (i.e., fluid resuscitation).

INTERVENTIONS

At 5 hrs (early sepsis) or 20 hrs (late sepsis) after cecal ligation and puncture, blood vessel-rich tissues (i.e., lungs) were harvested. The expression of CYP isoforms at both messenger RNA and protein levels was determined by reverse transcription polymerase chain reaction and Western blot analysis (CYP2C11), respectively. Hemodynamic variables were measured by radioactive microspheres.

MAIN RESULTS

The results indicate that the gene expression of CYP2C11 and CYP2J4 was significantly down-regulated at 20 hrs after cecal ligation and puncture, whereas the expression of CYP4A3 was markedly up-regulated at 5 hrs. The protein concentrations of CYP2C11 also decreased significantly at 20 hrs after cecal ligation and puncture. Although total peripheral resistance markedly increased, mean arterial pressure did not change significantly at 20 hrs after the onset of sepsis. In contrast, cardiac output and pulmonary perfusion markedly decreased in late sepsis.

CONCLUSIONS

Since the up-regulated CYP4A3 is associated with the early, hyperdynamic phase of sepsis and the down-regulated CYP2C11 and CYP2J4 are associated with the late, hypodynamic phase, vascular CYP isoforms that metabolize arachidonic acid may be involved in regulating the cardiovascular response during the progression of sepsis.

Intrinsic signals in the sexually dimorphic circulating growth hormone profiles of the rat

Male rats secrete growth hormone (GH) in episodic bursts every 3.5-4 h. Between the peaks, GH levels are undetectable. In females, GH secretory profiles are characterized as continuous because hormone concentrations are always measurable in the circulation. These gender differences in the circulating GH profiles are responsible, to varying degrees, for observed sexual dimorphisms ranging from body growth to the expression of hepatic cytochrome P450 (P450, CYP) isoforms. Using hypophysectomized rats in which restored gender-dependent plasma GH profiles were manipulated, we have investigated the importance of the interpulse period in the masculine episodic plasma GH profile in regulating expression (mRNA, protein and/or specific catalytic activity) of male-specific CYP2A2, 2C11, 2C13 and 3A2, female-specific CYP2C12 and female-predominant CYP2A1, 2C6 and 2C7. We observed that some isoforms were induced or suppressed by discerning the length of the GH-devoid interpulse period, others responded to the pulse amplitudes, still others recognized the mean circulating concentrations of GH and some were regulated by a combination of these signals. We conclude that concealed in the gender-dependent circulating GH profiles are numerous intrinsic signals, both inductive and repressive, individually "tailored" to be recognized by each isoform of P450. There would appear to be no one signal in each gender-dependent GH profile responsible, in toto, for the characteristic sexually dimorphic expression of some dozen hepatic P450s in male and female rats.