The IRE1α-XBP1 Pathway of the Unfolded Protein Response Is Required for Adipogenesis

SummarySignaling cascades during adipogenesis culminate in the expression of two essential adipogenic factors, PPARγ and C/EBPα. Here we demonstrate that the IRE1α-XBP1 pathway, the most conserved branch of the unfolded protein response (UPR), is indispensable for adipogenesis. Indeed, XBP1-deficient mouse embryonic fibroblasts and 3T3-L1 cells with XBP1 or IRE1α knockdown exhibit profound defects in adipogenesis. Intriguingly, C/EBPβ, a key early adipogenic factor, induces Xbp1 expression by directly binding to its proximal promoter region. Subsequently, XBP1 binds to the promoter of Cebpa and activates its gene expression. The posttranscriptional splicing of Xbp1 mRNA by IRE1α is required as only the spliced form of XBP1 (XBP1s) rescues the adipogenic defect exhibited by XBP1-deficient cells. Taken together, our data show that the IRE1α-XBP1 pathway plays a key role in adipocyte differentiation by acting as a critical regulator of the morphological and functional transformations during adipogenesis

Coombs Positive Thrombotic Thrombocytopenic Purpura in a Male Pediatric Patient: An Urgent Diagnostic Challenge

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy often caused by deficiency of von Willebrand (vW) factor cleaving protease, ADAMTS-13, leading to large vW multimers and intravascular platelet aggregation. Hemolysis in TTP is mechanical and nonimmune mediated, thus Coombs testing is usually negative. We report a case of an adolescent with thrombocytopenia and Coombs positive anemia, diagnosed with Evans syndrome, but ultimately found to have TTP. TTP should be considered in children with thrombocytopenia and Coombs positive anemia who are refractory to steroids or develop signs of microangiopathy. Recognition of this presentation can lead to life-saving treatment with plasma exchange

MON-178 Cyclical Cushing’s Syndrome in 12 Patients with Ectopic ACTH Secretion

Background : Cyclical Cushing’s syndrome (CCS) is characterized by alternating periods of endogenous hypercortisolism and eucortisolism. A literature survey of 60 adult patients with CCS found 15 to have ectopic ACTH secretion (EAS) (1). The duration and frequency of hypercortisolemia are unpredictable, creating a diagnostic challenge. Objective : Describe biochemical and clinical characteristics of patients with CCS due to occult or histologically proven ectopic ACTH-secreting neuroendocrine tumor (NET). Methods : We conducted a retrospective medical record review of 12 adults with EAS admitted to our institution. Inclusion required 1) evidence of ectopic ACTH tumor from biochemical testing (CRH stimulation, 8 mg dexamethasone suppression [DST], and/or inferior petrosal sinus sampling [IPSS]) or pathology results and 2) cycles of hypercortisolism (Hi-F) to eucortisolism (Eu-F) off medical treatment. Results : Average age on admission was 61 (46-79) years; 58% were women. All 12 had biochemical evidence of ACTH-dependent Hi-F. IPSS results suggested EAS in 9 patients, 8 of whom had Hi-F for more than two months, and 1 whose cycles occurred every 5 - 7 days. IPSS was consistent with Cushing’s disease (CD) in 2 patients after Hi-F of only 6 -7 weeks and one with Eu-F on admission, estimated duration < 4 weeks. DST suggested EAS in 9 patients, and CD in the one with recent Eu-F. CRH was consistent with EAS in 10 patients, but suggested CD in 2 with marginal increases in ACTH (34.5%, 38%) but not cortisol. 7 patients had ACTH-secreting tumor on pathology (5 pulmonary, 1 pancreas, 1 appendix NET), and 5 had occult presumed EAS. Time from one Hi-F episode to the next ranged from 1 week to 6 years with Hi-F duration of 3 days to 5 years. 24-hour urine free cortisol (UFC) levels were 17 - 301 times the upper reference range (RR) during Hi-F periods. During Eu-F, lowest UFCs were within RR in 9 patients and subnormal in 3. Hypokalemia occurred in 11 patients with Hi-F; increasing values paralleled movement to Eu-F. Conclusion : Patients with possible ectopic ACTH-secretion and CCS may pose a diagnostic challenge: clinical and biochemical evidence of hypercortisolemia may not be present, depending on the timing and/or duration of hypercortisolism. Furthermore, test results may inappropriately suggest Cushing’s disease if performed after less than 8 weeks of hypercortisolism, or with recent eucortisolism. Thus, weekly UFC measurement may facilitate diagnosis of cyclical Cushing’s syndrome and determine appropriate timing of dynamic testing such as inferior petrosal sinus sampling. Potassium may be a useful marker to determine when medical treatment can be tapered or stopped. 1. Meinardi JR, et al. Eur J Endocrinol. 157:245, 2007