Preferential biological processes in the human limbus by differential gene profiling.

Corneal epithelial stem cells or limbal stem cells (LSCs) are responsible for the maintenance of the corneal epithelium in humans. The exact location of LSCs is still under debate, but the increasing need for identifying the biological processes in the limbus, where LSCs are located, is of great importance in the regulation of LSCs. In our current study we identified 146 preferentially expressed genes in the human limbus in direct comparison to that in the cornea and conjunctiva. The expression of newly identified limbal transcripts endomucin, fibromodulin, paired-like homeodomain 2 (PITX2) and axin-2 were validated using qRT-PCR. Further protein analysis on the newly identified limbal transcripts showed protein localization of PITX2 in the basal and suprabasal layer of the limbal epithelium and very low expression in the cornea and conjunctiva. Two other limbal transcripts, frizzled-7 and tenascin-C, were expressed in the basal epithelial layer of the limbus. Gene ontology and network analysis of the overexpressed limbal genes revealed cell-cell adhesion, Wnt and TGF-β/BMP signaling components among other developmental processes in the limbus. These results could aid in a better understanding of the regulatory elements in the LSC microenvironment

Preferential Biological Processes in the Human Limbus by Differential Gene Profiling

<div><p>Corneal epithelial stem cells or limbal stem cells (LSCs) are responsible for the maintenance of the corneal epithelium in humans. The exact location of LSCs is still under debate, but the increasing need for identifying the biological processes in the limbus, where LSCs are located, is of great importance in the regulation of LSCs. In our current study we identified 146 preferentially expressed genes in the human limbus in direct comparison to that in the cornea and conjunctiva. The expression of newly identified limbal transcripts endomucin, fibromodulin, paired-like homeodomain 2 (PITX2) and axin-2 were validated using qRT-PCR. Further protein analysis on the newly identified limbal transcripts showed protein localization of PITX2 in the basal and suprabasal layer of the limbal epithelium and very low expression in the cornea and conjunctiva. Two other limbal transcripts, frizzled-7 and tenascin-C, were expressed in the basal epithelial layer of the limbus. Gene ontology and network analysis of the overexpressed limbal genes revealed cell-cell adhesion, Wnt and TGF-β/BMP signaling components among other developmental processes in the limbus. These results could aid in a better understanding of the regulatory elements in the LSC microenvironment.</p></div

Protein expression of selected limbal transcripts in human ocular tissue.

<p>A) Minimal expression of PITX2 was observed in the cornea. B) Distinct PITX2 cytoplasmic expression was present in pockets within the basal layer and suprabasal layer of the limbal epithelium. Insert highlights both PITX2 cytoplasmic and nuclear localization in the basal epithelial cells. Thin arrows indicate cells with PITX2 nuclear localization. C) Minimal expression of PITX2 was also observed in the conjunctiva. D) Weak expression of FZD7 was detected in the basal layer of the cornea. E) Highly localized FZD7 expression was observed at the basal layer of the limbal epithelium. F) We observed low expression in the suprabasal and superficial layers of the conjunctiva for FZD7. G) Minimal expression of TNC was observed in the cornea, while distinct expression was present in the subepithelial stroma along the limbus (H). (I) We detected minor expression of TNC in the suprabasal and superficial layers of the conjunctiva. Thick arrows represent examples of superficial epithelial cells and arrowheads represent examples of basal epithelial cells in the limbus. Scale bar, 50 µm.</p

Network map of preferentially expressed signature limbal genes.

<p>The IPA network map highlights the upregulation of genes from the TGF-β pathway and extracellular matrix processes. Fibronectin-1 is centrally connected to a number of upregulated limbal genes.</p

Comparison of mRNA expression levels between microarray and qRT-PCR of selected transcripts.

<p>All 9 transcripts were preferentially expressed in the limbus and minimally expressed in the cornea and conjunctiva. White bars represent the microarray results and black bars represent the qRT-PCR results. Similar expression patterns were observed between the microarray and qRT-PCR.</p

Gene ontology analysis of preferentially expressed signature limbal genes.

<p>Bar graph showing significance of enrichments terms from preferentially expressed genes in the limbal tissue.</p

Analysis of preferential transcription in the limbus compared to the cornea and conjunctiva.

<p>A) Venn diagram of 216 preferentially expressed limbal transcripts (including unknown and overlapping probes) between the limbal over corneal and conjunctival transcripts. B) Heat map of the 216 preferentially expressed limbal transcripts (including unknown and overlapping probes) between the limbal over corneal and conjunctival transcripts categorized by anatomical tissue. Red signifies overexpression and blue signifies underexpression.</p

Quality of Acute Stroke Care at Primary Stroke Centers Before and After Certification in Comparison to Never-Certified Hospitals.

Background and Purpose: Primary stroke center (PSC) certification is associated with improvements in stroke care and outcome. However, these improvements may reflect a higher baseline level of care delivery in hospitals eventually achieving certification. This study examines whether advancements in acute stroke care at PSCs are due to certification or factors intrinsic to the hospital. Methods: Data was obtained from the Field Administration of Stroke Therapy-Magnesium (FAST-MAG) trial with participation of 40 Emergency Medical System agencies, 315 ambulances, and 60 acute receiving hospitals in Los Angeles and Orange Counties. Subjects were transported to one of three types of destinations: PSC certified hospitals (PSCs), hospitals that were not PSCs at time of enrollment but would later become certified (pre-PSCs), and hospitals that would never be certified (non-PSCs). Metrics of acute stroke care quality included time arrival to imaging, use of intravenous tPA, and arrival to treatment. Results: Of 1,700 cases, 856(50%) were at certified PSCs, 529(31%) were at pre-PSCs, and 315 (19%) were at non-PSCs. Mean (SD) was 33min (±76.1) at PSCs, 47(±86.6) at pre-PSCs, and 49(±71.7) at non-PSCs. Of 1,223 cerebral ischemia cases, rate of tPA utilization was 43% at PSCs, 27% at pre-PSCs, and 28% at non-PSCs. Mean ED arrival to thrombolysis was 71(±32.7) at PSC, 98(±37.6) at pre-PSC, and 95(±45.0) at non-PSCs. PSCs had improved time to imaging (p = 0.014), percent tPA use (p &lt; 0.001), and time to treatment (p = 0.003). Conclusions: Stroke care at hospitals prior to PSC certification is equivalent to care at non-PSCs. Clinical Trial Registration: http://www.clinicaltrials.gov. Unique identifier: NCT00059332