Mutation in human CLPX elevates levels of δ-aminolevulinate synthase and protoporphyrin IX to promote erythropoietic protoporphyria

Loss-of-function mutations in genes for heme biosynthetic enzymes can give rise to congenital porphyrias, eight forms of which have been described. The genetic penetrance of the porphyrias is clinically variable, underscoring the role of additional causative, contributing, and modifier genes. We previously discovered that the mitochondrial AAA+ unfoldase ClpX promotes heme biosynthesis by activation of δ-aminolevulinate synthase (ALAS), which catalyzes the first step of heme synthesis. CLPX has also been reported to mediate heme-induced turnover of ALAS. Here we report a dominant mutation in the ATPase active site of human CLPX, p.Gly298Asp, that results in pathological accumulation of the heme biosynthesis intermediate protoporphyrin IX (PPIX). Amassing of PPIX in erythroid cells promotes erythropoietic protoporphyria (EPP) in the affected family. The mutation in CLPX inactivates its ATPase activity, resulting in coassembly of mutant and WT protomers to form an enzyme with reduced activity. The presence of low-activity CLPX increases the posttranslational stability of ALAS, causing increased ALAS protein and ALA levels, leading to abnormal accumulation of PPIX. Our results thus identify an additional molecular mechanism underlying the development of EPP and further our understanding of the multiple mechanisms by which CLPX controls heme metabolism. Keywords: heme biosynthesis; porphyria; ALAS; protein unfoldases; AAA+ ATPaseNational Institutes of Health (U.S.) (Grant F32 DK095726)National Institutes of Health (U.S.) (Grant R01 GM049224

Association of Elevated Body Mass Index With Functional Outcome and Mortality Following Acute Ischemic Stroke: The Obesity Paradox Revisited

BACKGROUND: Previous literature has identified a survival advantage in acute ischemic stroke (AIS) patients with elevated body mass indices (BMIs), a phenomenon termed the obesity paradox. OBJECTIVE: The aim of this study was to evaluate the independent association between obesity and clinical outcomes following AIS. METHODS: Weighted discharge data from the National Inpatient Sample were queried to identify AIS patients from 2015 to 2018. Multivariable logistic regression and Cox proportional hazards modeling were performed to evaluate associations between obesity (BMI ≥ 30) and clinical endpoints following adjustment for acute stroke severity and comorbidity burden. RESULTS: Among 1,687,805 AIS patients, 216,775 (12.8%) were obese. Compared to nonobese individuals, these patients were younger (64 vs. 72 mean years), had lower baseline NIHSS scores (6.9 vs. 7.9 mean score), and a higher comorbidity burden. Multivariable analysis demonstrated independent associations between obesity and lower likelihood of mortality (adjusted odds ratio [aOR] 0.76, 95% confidence interval [CI]: 0.71, 0.82, p \u3c 0.001; hazard ratio 0.84, 95% CI: 0.73, 0.97, p = 0.015), intracranial hemorrhage (aOR 0.87, 95% CI: 0.82, 0.93, p \u3c 0.001), and routine discharge to home (aOR 0.97, 95% CI: 0.95, 0.99; p = 0.015). Mortality rates between obese and nonobese patients were significantly lower across stroke severity thresholds, but this difference was attenuated among high severity (NIHSS \u3e 20) strokes (21.6% vs. 23.2%, p = 0.358). Further stratification of the cohort into BMI categories demonstrated a U-shaped association with mortality (underweight aOR 1.58, 95% CI: 1.39, 1.79; p \u3c 0.001, overweight aOR 0.64, 95% CI: 0.42, 0.99; p = 0.046, obese aOR 0.77, 95% CI: 0.71, 0.83; p \u3c 0.001, severely obese aOR 1.18, 95% CI: 0.74, 1.87; p = 0.485). Sub-cohort assessment of thrombectomy-treated patients demonstrated an independent association of obesity (BMI 30-40) with lower mortality (aOR 0.79, 95% CI: 0.65, 0.96; p = 0.015), but not with routine discharge. CONCLUSION: This cross-sectional analysis demonstrates a lower likelihood of discharge to home as well as in-hospital mortality in obese patients following AIS, suggestive of a protective effect of obesity against mortality but not against all poststroke neurological deficits in the short term which would necessitate placement in acute rehabilitation and long-term care facilities

FAM210B is an erythropoietin target and regulates erythroid heme synthesis by controlling mitochondrial iron import and ferrochelatase activity.

Erythropoietin (EPO) signaling is critical to many processes essential to terminal erythropoiesis. Despite the centrality of iron metabolism to erythropoiesis, the mechanisms by which EPO regulates iron status are not well-understood. To this end, here we profiled gene expression in EPO-treated 32D pro-B cells and developing fetal liver erythroid cells to identify additional iron regulatory genes. We determined that FAM210B, a mitochondrial inner-membrane protein, is essential for hemoglobinization, proliferation, and enucleation during terminal erythroid maturation. Fam210b deficiency led to defects in mitochondrial iron uptake, heme synthesis, and iron-sulfur cluster formation. These defects were corrected with a lipid-soluble, small-molecule iron transporter, hinokitiol, in Fam210b-deficient murine erythroid cells and zebrafish morphants. Genetic complementation experiments revealed that FAM210B is not a mitochondrial iron transporter but is required for adequate mitochondrial iron import to sustain heme synthesis and iron-sulfur cluster formation during erythroid differentiation. FAM210B was also required for maximal ferrochelatase activity in differentiating erythroid cells. We propose that FAM210B functions as an adaptor protein that facilitates the formation of an oligomeric mitochondrial iron transport complex, required for the increase in iron acquisition for heme synthesis during terminal erythropoiesis. Collectively, our results reveal a critical mechanism by which EPO signaling regulates terminal erythropoiesis and iron metabolism

Erythropoietin signaling regulates heme biosynthesis. 1

Abstract 34 Heme is required for survival of all cells, and in most eukaryotes, is produced through a 35 series of eight enzymatic reactions. Although heme production is critical for many 36 cellular processes, how it is coupled to cellular differentiation is unknown. Here, usin