Publications

Medullary thymic epithelial cells (mTECs) facilitate the deletion of developing self-reactive T cells by displaying a diverse repertoire of tissue-specific antigens, a process which largely depends on the expression of the autoimmune regulator (Aire) gene. Mature microRNAs (miRNAs) that regulate gene expression post-transcriptionally are generated in a multistep process. The microprocessor complex, including DGCR8, cleaves canonical miRNAs, but alternative DGCR8-independent miRNA biogenesis pathways exist as well. In order to study the role of canonical miRNAs in thymic epithelial cells (TECs), we ablated Dgcr8 using a FoxN1-Cre transgene. We report that DGCR8-deficient TECs are unable to maintain proper thymic architecture and exhibit a dramatic loss of thymic cellularity. Importantly, DGCR8-deficient TECs develop a severe loss of Aire(+) mTECs. Using a novel immunization approach to amplify and detect self-reactive T cells within a polyclonal TCR repertoire, we demonstrate a link between the loss of Aire expression in DGCR8-deficient TECs and the breakdown of negative selection in the thymus. Thus, DGCR8 and canonical miRNAs are important in TECs for supporting central tolerance.

BACKGROUND

Numerous studies indicate that the use of feeding tubes (FT) in persons with advanced cognitive impairment (CI) does not improve clinical outcomes or survival, and results in higher rates of hospitalization and emergency department (ED) visits. It is not clear, however, whether such risk varies by resident level of CI and whether these ED visits and hospitalizations are potentially preventable. The objective of this study was to determine the rates of ED visits, hospitalizations and potentially preventable ambulatory care sensitive (ACS) ED visits and ACS hospitalizations for long-stay NH residents with FTs at differing levels of CI.

METHODS

We linked Centers for Medicare and Medicaid Services inpatient & outpatient administrative claims and beneficiary eligibility data with Minimum Data Set (MDS) resident assessment data for nursing home residents with feeding tubes in a 5% random sample of Medicare beneficiaries residing in US nursing facilities in 2006 (n = 3479). Severity of CI was measured using the Cognitive Performance Scale (CPS) and categorized into 4 groups: None/Mild (CPS = 0-1, MMSE = 22-25), Moderate (CPS = 2-3, MMSE = 15-19), Severe (CPS = 4-5, MMSE = 5-7) and Very Severe (CPS = 6, MMSE = 0-4). ED visits, hospitalizations, ACS ED visits and ACS hospitalizations were ascertained from inpatient and outpatient administrative claims. We estimated the risk ratio of each outcome by CI level using over-dispersed Poisson models accounting for potential confounding factors.

RESULTS

Twenty-nine percent of our cohort was considered "comatose" and "without any discernible consciousness", suggesting that over 20,000 NH residents in the US with feeding tubes are non-interactive. Approximately 25% of NH residents with FTs required an ED visit or hospitalization, with 44% of hospitalizations and 24% of ED visits being potentially preventable or for an ACS condition. Severity of CI had a significant effect on rates of ACS ED visits, but little effect on ACS hospitalizations.

CONCLUSIONS

ED visits and hospitalizations are common in cognitively impaired tube-fed nursing home residents and a substantial proportion of ED visits and hospitalizations are potentially preventable due to ACS conditions.