Publications

Corneal epithelial stem cells are known to be localized to the basal layer of the limbal epithelium, providing a model system for epithelial stem cell biology; however, the mechanisms regarding the maintenance of these stem cells in their specialized niche remain poorly understood. N-cadherin is a member of the classic cadherin family and has previously been demonstrated to be expressed by hematopoietic stem cells. In the present study, we demonstrate that N-cadherin is expressed by putative stem/progenitor cells, as well as melanocytes, in the human limbal epithelial stem cell niche. In addition, we demonstrate that upon in vitro culture using 3T3 feeder layers, loss of N-cadherin expression occurs with cell proliferation. These results indicate that N-cadherin may be a critical cell-to-cell adhesion molecule between corneal epithelial stem/progenitor cells and their corresponding niche cells in the limbal epithelium.

Normal rat pregnancy is characterized by plasma volume expansion due to renal sodium retention and is associated with a blunted response to natriuretic stimuli, such as atrial natriuretic peptide (ANP). ANP signals via cGMP, and phosphodiesterases (PDE) inactivate cGMP and terminate the natriuretic response. We previously reported that increased medullary PDE-5 activity occurs in rat pregnancy, which may be the mechanism of the blunted natriuretic effect of ANP. Here, we used anesthetized 16-day pregnant and virgin rats to investigate whether intrarenal infusion of a selective PDE-5 inhibitor, sildenafil, would reverse the blunted response to ANP in pregnancy. We measured blood pressure, renal clearances using inulin and p-aminohippuric acid, and electrolyte excretion at baseline and during an ANP infusion. ANP caused a fall in mean arterial pressure in all groups, and sildenafil induced a further reduction. We observed an increase in sodium excretion with ANP in all rats, but this was blunted in the vehicle-infused pregnant rats. This could not be explained by differences in renal hemodynamics and was of tubular origin, as reflected by the reduced rise in fractional excretion of sodium with ANP in the pregnant rat given vehicle (45 +/- 11 vs. 204 +/- 49%; P < 0.05). However, intrarenal sildenafil increased the natriuretic response and the rise in fractional excretion of sodium to the virgin value (226 +/- 23 vs. 245 +/- 73%; not significant), whereas the blunting persisted in the contralateral kidney. This demonstrates that increased intrarenal PDE-5 mediates the blunted natriuretic response to ANP during pregnancy and may contribute to the physiological volume expansion.

BACKGROUND

The prostanoid DP receptor (PTGDR) gene on chromosome 14q22.1 has been identified as an asthma susceptibility gene. A haplotype with decreased transcription factor binding and transcription efficiency was associated with decreased asthma susceptibility in African American and white subjects. The significance of PTGDR gene variants in asthma has yet to be determined in Latinos, the largest US minority population, nor has the association been replicated in other populations.

OBJECTIVE

To determine the role of PTGDR gene variants in asthma susceptibility and asthma-related traits among the Mexican, Puerto Rican, and African American populations.

METHODS

We determined whether single nucleotide polymorphisms (SNPs) and haplotypes in PTGDR were associated with asthma and asthma-related traits by family-based and cross-sectional cohort analyses in 336 Puerto Rican and 273 Mexican asthmatic trios and by case-control analysis among African American subjects with asthma and healthy controls (n = 352).

RESULTS

We identified 13 SNPs in the PTGDR gene, and 6 were further analyzed. There was no significant association between PTGDR variants and asthma by family-based or case-control analyses. SNPs -441C and -197C and haplotype TTT showed marginal association with asthma-related traits in Mexican subjects. SNP -441 genotype TT (P = .05) and haplotype TTT (P = .02) were associated with increased IgE levels in African Americans.

CONCLUSION

We conclude that the PTGDR gene is not a significant risk factor for asthma among Puerto Ricans, Mexicans, or African Americans.

CLINICAL IMPLICATIONS

Asthma candidate genes provide insights to pathophysiology and potentially new therapeutic targets, although the PTGDR gene was not found to be a significant risk factor for asthma in 3 populations.

BACKGROUND

Sphingosine kinase (SKase) has been implicated in the protection of hearts from ischemia/reperfusion injury. This hypothesis was further examined.

MATERIAL/METHODS

Changes in SKase activity and cardiac function (left ventricular developed pressure, LVDP, and infarct size) in response to ischemia and reperfusion were studied in adult rat hearts by the ex vivo Langendorff method. Following initial equilibration or preconditioning, there was 45 min no-flow ischemia and then 45 min of reperfusion.

RESULTS

SKase activity declined 61% during ischemia and did not recover upon reperfusion. LVDP also did not recover upon reperfusion and the infarct size was 47%. A short 30 min period of ischemia was associated with variable recovery of SKase activity that directly correlated with LVDP recovery. Preconditioning of hearts reduced the decrease in SKase activity during ischemia by half, and upon reperfusion activity returned to normal. The LVDP recovered 79% and infarct size was small. Preconditioned hearts had higher S-1-P levels after ischemia/reperfusion relative to non-preconditioned hearts. The decline in SKase activity during ischemia of preconditioned hearts could not be mimicked in vitro by treatment with protein phosphatases. Attempts to alter activity of SKase from control, preconditioned, ischemic, or reperfused hearts by phosphorylation with ERK1/2 were unsuccessful. Treatment of non-preconditioned hearts at reperfusion with 100 nM S-1-P improved recovery of LVDP. The SKase inhibitor dimethylsphingosine blocked hemodynamic recovery in preconditioned hearts.

CONCLUSIONS

The data support a role for SKase activity in recovery of hemodynamic function after ischemic injury and also in the cardioprotective effect of preconditioning.