Publications

Recently, cell-based therapies have developed as a foundation for regenerative medicine. General approaches for cell delivery have thus far involved the use of direct injection of single cell suspensions into the target tissues. Additionally, tissue engineering with the general paradigm of seeding cells into biodegradable scaffolds has also evolved as a method for the reconstruction of various tissues and organs. With success in clinical trials, regenerative therapies using these approaches have therefore garnered significant interest and attention. As a novel alternative, we have developed cell sheet engineering using temperature-responsive culture dishes, which allows for the non-invasive harvest of cultured cells as intact sheets along with their deposited extracellular matrix. Using this approach, cell sheets can be directly transplanted to host tissues without the use of scaffolding or carrier materials, or used to create in vitro tissue constructs via the layering of individual cell sheets. In addition to simple transplantation, cell sheet engineered constructs have also been applied for alternative therapies such as endoscopic transplantation, combinatorial tissue reconstruction, and polysurgery to overcome limitations of regenerative therapies and cell delivery using conventional approaches.

The renin-angiotensin system is implicated in the development of a variety of human diseases. Many studies have sought to characterize the clinical implications of polymorphisms in the angiotensin converting enzyme (ACE) gene. Given the high mortality rate of individuals on chronic hemodialysis (HD), we sought to investigate whether genetic diversity in the ACE gene correlates with mortality in this population. We assembled a racially diverse cohort of prevalent individuals on chronic outpatient HD, and followed it prospectively for a mean of 2.1 years. Subjects were genotyped for seven single nucleotide polymorphisms (SNPs) in the ACE gene. Haplotype probabilities were calculated using an expectation-maximization algorithm. Cox proportional hazards regression was used to determine associations between haplotype and time to mortality from initiation of HD. There was strong linkage disequilibrium (LD) across the ACE gene, with three tagging SNPs found to account for all seven-SNP haplotypes that had a frequency of greater than 4%. After adjustment for age, race, gender, and diabetes status, a three-locus haplotype was associated with a 72% risk reduction in mortality (P = 0.004). The majority of this association was captured by the TT genotype of A-239T promoter polymorphism. The TGG (non-wild-type) haplotype, consisting of three tagging SNPs in the ACE gene, is associated with significantly decreased risk of all-cause mortality in HD patients independent of age, race, gender, and diabetic status. This "protective" haplotype may encompass loci with functional significance in the ACE gene.

Lung endothelial damage is a characteristic morphological feature of ischemia-reperfusion (I/R) injury, although the molecular steps involved in the loss of endothelial integrity are still poorly understood. We tested the hypothesis that the activation of vascular endothelial growth factor (VEGF) cell signaling would be responsible for the increase in lung vascular permeability seen early after the onset of I/R in rats. Furthermore, we hypothesized that the I/R-induced pulmonary edema would be significantly attenuated in rats by the activation of the stress protein response. Pretreatment with Ad Flk-1, an adenovirus encoding for the soluble VEGF receptor type II, prevented I/R-mediated increase in lung vascular permeability in rats. Furthermore, the I/R-induced lung injury was significantly decreased by prior activation of the stress protein response with geldanamycin or pyrrolidine dithiocarbamate. In vitro studies demonstrated that VEGF caused an increase in protein permeability across primary cultures of bovine macro- and microvascular lung endothelial cell monolayers that were associated with a phosphorylation of VE- and E-cadherin and the formation of actin stress fibers. Activation of the stress protein response prevented the VEGF-mediated changes in protein permeability across these cell monolayers and reduced the phosphorylation of VE-and E-cadherins, as well as the formation of actin stress fibers in these cells.

To determine the value of human immunodeficiency virus type 1 (HIV-1) RNA level in distinguishing HIV-associated nephropathy from non-HIV-associated nephropathy renal pathological conditions, we retrospectively compared renal histopathological findings for 86 HIV-infected patients according to HIV-1 RNA levels. We found that HIV-associated nephropathy was unlikely among patients with HIV-1 RNA levels <400 copies/mL. Hypertensive vascular disease surpassed HIV-associated nephropathy as the most common renal pathological finding among the entire cohort. HIV-1 RNA level did not correlate with renal survival.

OBJECTIVE

N, N-Dimethylsphingosine (DMS) is recognized as an inhibitor of sphingosine kinase (SphK), a key enzyme responsible for the formation of sphingosine-1-phosphate (S1P). We previously showed that S1P was cardioprotective and that SphK was critical for myocardial ischemic preconditioning. Although DMS is an endogenous sphingolipid, its effect on cardiac function and cardioprotection at low concentration has not been studied.

METHODS

In Langendorff-perfused wild-type and protein kinase C (PKC)epsilon-null mouse hearts, cardiac function, infarction size, and SphK activity were measured.

RESULTS

Pretreatment with 0.3 microM and 1 microM DMS for 10 min protected against ischemia/reperfusion injury. Cardiac function (LVDP, +/-dP/dtmax) was improved and infarction size was reduced. The cardiac protection induced by DMS was abolished in PKCepsilon-null mouse hearts. Administration of 1 microM DMS ex vivo increased cytosolic SphK activity. This enhanced SphK activity was abolished in PKCepsilon-null mouse hearts. DMS also increased PKCepsilon translocation from the particulate to the cytosolic fraction with no effect on PKCalpha distribution. Co-immunoprecipitation showed that SphK1 interacted with PKCepsilon phosphorylated on Ser729. DMS also increased cytosolic Akt phosphorylation (Ser 473) and Akt translocation from a Triton-insoluble fraction to the cytosol.

CONCLUSIONS

DMS has a biphasic effect on cardioprotection. Higher concentrations (10 microM) are inhibitory, whereas a low concentration (0.3 microM and 1 microM) of DMS protects murine hearts against ischemia/reperfusion injury. DMS activates SphK in the cytosol via a PKCepsilon dependent mechanism. The PKCepsilon-SphK-S1P-Akt pathway is involved in the cardiac protection induced by DMS.