Connexin43 (Cx43) is a gap junction protein that forms multimeric channels that enable intercellular communication through the direct transfer of signals and metabolites. Although most multimeric protein complexes form in the endoplasmic reticulum (ER), Cx43 seems to exit from the ER as monomers and subsequently oligomerizes in the Golgi complex. This suggests that one or more protein chaperones inhibit premature Cx43 oligomerization in the ER. Here, we provide evidence that an ER-localized, 29-kDa thioredoxin-family protein (ERp29) regulates Cx43 trafficking and function. Interfering with ERp29 function destabilized monomeric Cx43 oligomerization in the ER, caused increased Cx43 accumulation in the Golgi apparatus, reduced transport of Cx43 to the plasma membrane, and inhibited gap junctional communication. ERp29 also formed a specific complex with monomeric Cx43. Together, this supports a new role for ERp29 as a chaperone that helps stabilize monomeric Cx43 to enable oligomerization to occur in the Golgi apparatus. INTRODUCTIONConnexins form gap junction channels that mediate intercellular communication by allowing the direct transfer of ions and small aqueous molecules between neighboring cells or by serving as hemichannels at the plasma membrane (Harris, 2001;Goodenough and Paul, 2003;Saez et al., 2003;Laird, 2006). There are Ͼ20 human connexin genes and one of the most ubiquitously expressed is connexin43 (Cx43). Several diseases have been linked to mutations in different connexin genes, including Cx43 (Kelsell et al., 2001;Laird, 2008). Many of these mutant connexins are not efficiently processed and lack the ability to form functional gap junction channels. Determining how mutant connexins are mistargeted requires a more complete understanding of how normal connexins are processed by the cell.A gap junction hemichannel consists of six connexins, which oligomerize before delivery to the plasma membrane (Martin and Evans, 2004;Segretain and Falk, 2004;Koval, 2006). Unlike most multimeric membrane channels, Cx43 is unusual in that it does not oligomerize in the endoplasmic reticulum (ER) (Musil and Goodenough, 1993), which is more commonly a prerequisite to further transport along the secretory pathway (Ellgaard and Helenius, 2003;Anelli and Sitia, 2008). Instead, Cx43 is transported out of the ER as an apparent monomer that then oligomerizes in the Golgi complex (Musil and Goodenough, 1993;Koval et al., 1997). Although other connexins, such as Cx46 (Koval et al., 1997), also oligomerize in the Golgi apparatus, this is not a universal pathway for connexin oligomerization because other gap junction proteins, such as Cx32, preferentially oligomerize in the ER (Martin and Evans, 2004;Koval, 2006). Understanding the molecular basis for this difference, as well as the ability of monomeric Cx43 to be transported from the ER to the Golgi apparatus has proven difficult, because little is known about chaperones that regulate connexin folding. In particular, it seemed likely that one or more chaperones would be requir...

BackgroundTargeted interventions have improved physical activity and wellness of medical residents. However, no exercise interventions have focused on emergency medicine residents.ObjectiveThis study aimed to measure the effectiveness of a wearable device for tracking physical activity on the exercise habits and wellness of this population, while also measuring barriers to adoption and continued use.MethodsThis pre-post cohort study enrolled 30 emergency medicine residents. Study duration was 6 months. Statistical comparisons were conducted for the primary end point and secondary exercise end points with nonparametric tests. Descriptive statistics were provided for subjective responses.ResultsThe physical activity tracker did not increase the overall self-reported median number of days of physical activity per week within this population: baseline 2.5 days (interquartile range, IQR, 1.9) versus 2.8 days (IQR 1.5) at 1 month (P=.36). There was a significant increase in physical activity from baseline to 1 month among residents with median weekly physical activity level below that recommended by the Centers for Disease Control and Prevention at study start, that is, 1.5 days (IQR 0.9) versus 2.4 days (IQR 1.2; P=.04), to 2.0 days (IQR 2.0; P=.04) at 6 months. More than half (60%, 18/30) of participants reported a benefit to their overall wellness, and 53% (16/30) reported a benefit to their physical activity. Overall continued use of the device was 67% (20/30) at 1 month and 33% (10/30) at 6 months.ConclusionsThe wearable physical activity tracker did not change the overall physical activity levels among this population of emergency medicine residents. However, there was an improvement in physical activity among the residents with the lowest preintervention physical activity. Subjective improvements in overall wellness and physical activity were noted among the entire study population.

We have used connexin constructs containing a C-terminal di-lysine-based endoplasmic reticulum (ER) retention/retrieval signal (HKKSL) transfected into HeLa cells to study early events in connexin oligomerization. Using this approach, we found that Cx43-HKKSL stably expressed at moderate levels by HeLa cells was retained in the ER and prevented from oligomerization. However, Cx43-HKKSL stably overexpressed by HeLa cells escaped from the ER and localized to a perinuclear region of the cell that included the Golgi apparatus. Overexpressed Cx43-HKKSL oligomerized into hexamers and also formed Triton X-100 insoluble, intracellular complexes that resembled gap junctions. Thus, the ability of HeLa cells to inhibit Cx43 oligomerization was saturable. HeLa cells stably overexpressing Cx43-HKKSL may provide a useful model system to evaluate pharmacologic agents and/or cDNAs encoding chaperones with the potential to regulate initial steps in Cx43 oligomerization.

Introduction: Undocumented immigrants are excluded from benefits that help compensate for scheduled outpatient hemodialysis (HD), compelling them to use emergency departments (ED) for HD. Consequently, these patients can receive “emergency-only” HD after presenting to the ED with critical illness due to untimely dialysis. Our objective was to describe the impact of emergency-only HD on hospital cost and resource utilization in a large academic health system that includes public and private hospitals. Methods: This retrospective observational study of health and accounting records took place at five teaching hospitals (one public, four private) over 24 consecutive months from January 2019 to December 2020. All patients had emergency and/or observation visits, renal failure codes (International Classification of Diseases, 10th Rev, Clinical Modification), emergency HD procedure codes, and an insurance status of “self-pay.” Primary outcomes included frequency of visits, total cost, and length of stay (LOS) in the observation unit. Secondary objectives included evaluating the variation in resource use between persons and comparing these metrics between the private and public hospitals. Results: A total of 15,682 emergency-only HD visits were made by 214 unique persons, for an average of 36.6 visits per person per year. The average cost per visit was $1,363, for an annual total cost of $10.7 million. The average LOS was 11.4 hours. This resulted in 89,027 observation-hours annually, or 3,709 observation-days. The public hospital dialyzed more patients compared to the private hospitals, especially due to repeat visits by the same persons. Conclusion: Health policies that limit hemodialysis of uninsured patients to the ED are associated with high healthcare costs and a misuse of limited ED and hospital resources.