Redistribution of clathrin-coated vesicle adaptor complexes during adipocytic differentiation of 3T3-L1 cells

Mechanisms for intracellular retention of proteins are induced during adipocytic differentiation of 3T3-L1 cells. To investigate the potential role of clathrin lattices in these retention processes, we performed a morphological and biochemical analysis of coated vesicle components in 3T3-L1 cells. Optical sectioning and image restoration revealed a marked increase in the staining of clathrin and beta adaptins in the perinuclear region of cells with differentiation. In addition, predominance of beta (subunit of the AP-2, plasma membrane adaptor) over beta\u27 (subunit of the AP-1, Golgi adaptor) adaptin was observed in immunoblots of clathrin-coated vesicles purified from nondifferentiated fibroblasts, and this ratio was reversed in coated vesicles purified from differentiated adipocytes. These results indicate that the relative abundance of TGN-derived clathrin lattices increases markedly during adipocytic differentiation. Subcellular fractionation indicated that cytosolic AP-1 and AP-2 adaptors comprised approximately 70% of the total cellular adaptor pool. Interestingly, neither the concentration nor the relative ratio of cytosolic AP-1 to AP-2 adaptors increased significantly during differentiation. These data suggest that the increase in TGN-derived lattices results from differentiation-induced mechanisms for enhanced assembly or stabilization of adaptors on Golgi membranes. Interestingly, double-immunofluorescence microscopy also revealed that whereas extensive colocalization between clathrin and beta adaptins occurred both in fibroblasts and adipocytes, structures stained only with anti-adaptin antibody could be detected. Taken together these results suggest that membranes coated with adaptors, but not clathrin, can exist in these cells

TGFβ receptor internalization into EEA1-enriched early endosomes: role in signaling to Smad2

Transforming growth factor (TGF)β is an important physiological regulator of cellular growth and differentiation. It activates a receptor threonine/serine kinase that phosphorylates the transcription factor Smad2, which then translocates into the nucleus to trigger specific transcriptional events. Here we show that activated type I and II TGFβ receptors internalize into endosomes containing the early endosomal protein EEA1. The extent of TGFβ-stimulated Smad2 phosphorylation, Smad2 nuclear translocation, and TGFβ-stimulated transcription correlated closely with the extent of internalization of the receptor. TGFβ signaling also requires SARA (Smad anchor for receptor activation), a 135-kD polypeptide that contains a FYVE Zn++ finger motif. Here we show that SARA localizes to endosomes containing EEA1, and that disruption of this localization inhibits TGFβ-induced Smad2 nuclear translocation. These results indicate that traffic of the TGFβ receptor into the endosome enables TGFβ signaling, revealing a novel function for the endosome as a compartment specialized for the amplification of certain extracellular signals

Syndromic congenital myelofibrosis associated with a loss-of-function variant in RBSN

The human proteins rabenosyn-5 and VPS45 form a complex that plays a key role in early endocytosis. Pathogenic variants in VPS45 cause severe congenital neutropenia (SCN) with impaired neutrophil function, reticulin fibrosis of the bone marrow, and extramedullary hematopoiesis (OMIM: 615285). Patients with a specific VPS45 variant (p.Glu238Lys) also have intellectual disability and bilateral optic nerve hypoplasia. To date, the only evidence of a potential role for RBSN in human disease is the report of a homozygous missense variant (p.Gly425Arg) in a patient with intellectual disability, seizures, microcephaly, osteopenia, mild reticulin fibrosis of the bone marrow, and transient neutropenia

Role of phosphatidylinositol 3-kinase and Rab5 effectors in phagosomal biogenesis and mycobacterial phagosome maturation arrest

Phagosomal biogenesis is a fundamental biological process of particular significance for the function of phagocytic and antigen-presenting cells. The precise mechanisms governing maturation of phagosomes into phagolysosomes are not completely understood. Here, we applied the property of pathogenic mycobacteria to cause phagosome maturation arrest in infected macrophages as a tool to dissect critical steps in phagosomal biogenesis. We report the requirement for 3-phosphoinositides and acquisition of Rab5 effector early endosome autoantigen (EEA1) as essential molecular events necessary for phagosomal maturation. Unlike the model phagosomes containing latex beads, which transiently recruited EEA1, mycobacterial phagosomes excluded this regulator of vesicular trafficking that controls membrane tethering and fusion processes within the endosomal pathway and is recruited to endosomal membranes via binding to phosphatidylinositol 3-phosphate (PtdIns[3]P). Inhibitors of phosphatidylinositol 3′(OH)-kinase (PI-3K) activity diminished EEA1 recruitment to newly formed latex bead phagosomes and blocked phagosomal acquisition of late endocytic properties, indicating that generation of PtdIns(3)P plays a role in phagosomal maturation. Microinjection into macrophages of antibodies against EEA1 and the PI-3K hVPS34 reduced acquisition of late endocytic markers by latex bead phagosomes, demonstrating an essential role of these Rab5 effectors in phagosomal biogenesis. The mechanism of EEA1 exclusion from mycobacterial phagosomes was investigated using mycobacterial products. Coating of latex beads with the major mycobacterial cell envelope glycosylated phosphatidylinositol lipoarabinomannan isolated from the virulent Mycobacterium tuberculosis H37Rv, inhibited recruitment of EEA1 to latex bead phagosomes, and diminished their maturation. These findings define the generation of phosphatidylinositol 3-phosphate and EEA1 recruitment as: (a) important regulatory events in phagosomal maturation and (b) critical molecular targets affected by M. tuberculosis. This study also identifies mycobacterial phosphoinositides as products with specialized toxic properties, interfering with discrete trafficking stages in phagosomal maturation

Association between First Trimester Pregnancy Associated Plasma Protein–A (PAPP-A) and Gestational Diabetes Mellitus Development

Background: Gestational diabetes (GDM) is a common pregnancy complication with significant cardiometabolic consequences for mothers and offspring. Previous research from our group suggests that adipose tissue IGFBP-5 and its unique metalloprotease PAPP-A (Pregnancy Associated Plasma Protein-A) may play mechanistic roles in GDM development by regulating functional IGF-1 levels and lipid storage and metabolism. Aim: To examine the relationship between circulating PAPP-A levels and GDM development. We hypothesized that high first trimester PAPP-A levels would be associated with decreased GDM risk. Methods: A retrospective cohort of women delivering singleton gestations at UMass Memorial Healthcare (2009, 2010, 2014, 2015) was assembled by abstracting electronic medical records. PAPP-A was measured in first trimester (11-14 weeks), and reported as quartiles of multiples of the mean (MoM) based on gestational age and adjusted for maternal weight and race/ethnicity. GDM diagnosis based on standard 2-step protocol (~24-28 weeks; failed 50g 1hr glucola screen then ≥2 abnormal values per Carpenter-Coustan criteria on 100g 3hr glucose tolerance test). Crude and multivariable-adjusted logistic regression models estimated the association between PAPP-A MoM quartiles and GDM. Results: Women (N=1,251) were 29.7 (SD:5.7) years old and 12.5 (SD:0.6) weeks gestation at PAPP-A measurement. 7.6% (n=95) developed GDM. Median PAPP-A MoM were 0.7 (inter-quartile range [IQR]=0.5-1.0) among women with GDM and 0.9 (IQR=0.6-1.3) among controls; 39% versus 23% were in the 1st quartile, respectively. After adjusting for pre-pregnancy body mass index, nuchal translucency, crown rump length, smoking status, and parity, women with PAPP-A MoM in 2nd, 3rd, and 4th quartiles had 52% (OR=0.48, 95%CI=0.26-0.88), 45% (OR=0.55, 95%CI=0.30-0.99) and 73% (OR=0.27, 95%CI=0.13-0.53) lower odds of GDM compared to women in the 1st quartile. Conclusion: Higher PAPP-A MoM levels were associated with lower GDM risk. Future studies will assess whether higher PAPP-A levels are associated with enhanced IGF-1 signaling and improved pregnancy metabolic homeostasis

Association between First Trimester Pregnancy Associated Plasma Protein–A and the Development of Gestational Diabetes Mellitus

Background: Gestational diabetes (GDM) is a common pregnancy complication with significant cardiometabolic consequences for mothers and offspring. Previous research from our group suggests that adipose tissue IGFBP-5 and its unique metalloprotease PAPP-A (Pregnancy Associated Plasma Protein-A) may play mechanistic roles in GDM development by regulating functional IGF-1 levels and lipid storage and metabolism. Aim: To examine the relationship between circulating PAPP-A levels and GDM development. We hypothesized that high first trimester PAPP-A levels would be associated with decreased GDM risk. Methods: A retrospective cohort of women delivering singleton gestations at UMass Memorial Healthcare (2009, 2010, 2014, 2015) was assembled by abstracting electronic medical records. PAPP-A was measured in first trimester (11-14 weeks), and reported as quartiles of multiples of the mean (MoM) based on gestational age and adjusted for maternal weight and race/ethnicity. GDM diagnosis based on standard 2-step protocol (~24-28 weeks; failed 50g 1hr glucola screen then ≥2 abnormal values per Carpenter-Coustan criteria on 100g 3hr glucose tolerance test). Crude and multivariable-adjusted logistic regression models estimated the association between PAPP-A MoM quartiles and GDM. Results: Women (N=1,251) were 29.7 (SD:5.7) years old and 12.5 (SD:0.6) weeks gestation at PAPP-A measurement. 7.6% (n=95) developed GDM. Median PAPP-A MoM were 0.7 (inter-quartile range [IQR]=0.5-1.0) among women with GDM and 0.9 (IQR=0.6-1.3) among controls; 39% versus 23% were in the 1st quartile, respectively. After adjusting for pre-pregnancy body mass index, nuchal translucency, crown rump length, smoking status, and parity, women with PAPP-A MoM in 2nd, 3rd, and 4th quartiles had 52% (OR=0.48, 95%CI=0.26-0.88), 45% (OR=0.55, 95%CI=0.30-0.99) and 73% (OR=0.27, 95%CI=0.13-0.53) lower odds of GDM compared to women in the 1st quartile. Conclusion: Higher PAPP-A MoM levels were associated with lower GDM risk. Future studies will assess whether higher PAPP-A levels are associated with enhanced IGF-1 signaling and improved pregnancy metabolic homeostasis

Adipose Tissue Architecture and Gestational Weight Gain in Normoglycemic Pregnancies

Objective: To investigate histologic architecture of subcutaneous (SQAT) and visceral adipose tissue (VAT) growth in relationship to gestational weight gain (GWG). Epidemiological data suggest that SQAT expansion may be protective of obesity related co-morbidities, whereas VAT expansion is associated with Type-2 diabetes risk. We hypothesized that in normal gravidas, GWG would be associated with hypertrophy of SQAT and not VAT. Methods: A subset of subjects enrolled in the Pregnancy & Postpartum Observational Dietary Study (PPODS) and undergoing Cesarean delivery had SQAT (midline superior edge Pfannenstiel incision) and VAT (inferior omental periphery) biopsies after neonatal delivery, uterine closure and hemostasis achievement. Excised tissues were fixed and stained. Average adipocyte size and capillary density were assessed in 10 independent sections per AT depot per subject. GWG determined by the difference of weight at first visit and immediately postpartum (1-4 days post-op). GWG plotted vs mean SQAT or VAT adipocyte size. Results: Table illustrates general clinical characteristics of the 5 subjects. Figure A demonstrates SQAT and VAT mean adipocyte size with representative sections from patient E depicted above bar graphs representing means and SEM from 5 patients. SQ adipocytes were significantly larger than those from VAT. Significant positive correlation was noted between GWG and SQAT adipocyte size (Figure B), but not VAT adipocyte size (Figure C). Discussion: Preliminary results reveal that in normal pregnancies, GWG is associated with changes in SQAT but not VAT architecture, which reflects lipid accumulation. These results are consistent with the model that SQAT is specifically adapted for healthy lipid storage, and provides a basis for comparison between normal gravidas and those with GDM

Understanding multifactorial influences on the continuum of maternal weight trajectories in pregnancy and early postpartum: study protocol, and participant baseline characteristics

BACKGROUND: Maternal and offspring immediate and long-term health are affected by pregnancy weight gain and maternal weight. This study was designed to determine feasibility of: 1) recruiting a socio-economically and racially/ethnically diverse sample of pregnant women into a longitudinal observational study, including consenting the women for serial biologic specimen evaluations; 2) implementing comprehensive assessments (including biologic, anthropometric, behavioral, cognitive/psychosocial and socio-demographic, and cultural measures) at multiple time points over the study period, including collecting biologic specimens at planned and unplanned pregnancy delivery times; and 3) retaining the sample for one year into the postpartum period. Additionally, the study will provide preliminary data of associations among hypothesized predictors, mediators and moderators of pregnancy and post-partum maternal and infant weight trajectories. The study was conceptualized under a Biopsychosocial Model using a lifespan approach. Study protocol and baseline characteristics are described. METHODS/DESIGN: We sought to recruit a sample of 100 healthy women age 18-45 years, between 28-34 weeks gestation, with singleton pregnancies, enrolled in care prior to 17 weeks gestation. Women provide written consent for face-to-face (medical history, anthropometrics, biologic specimens), and paper-and-pencil assessments, at five time points: baseline (third trimester), delivery-associated, and 6-weeks, 3-months and 6-months postpartum. Additional telephone-based assessments (diet, physical activity and breastfeeding) administered baseline and three-months postpartum. Infant weights are collected until 1-year of life. We seek to retain 80% of participants at six-months postpartum and 80% of offspring at 12-months. 110 women were recruited. Sample characteristics include: mean age 28.3 years, BMI 25.7 kg/m(2), and gestational age at baseline visit of 32.5 weeks. One-third of cohort was non-white, over a quarter were Latina, and almost a quarter were non-US born. The cohort majority was multigravida, had graduated high school and/or had higher levels of education, and worked outside the home. DISCUSSION: Documentation of study feasibility and preliminary data for theory-driven hypothesis of maternal and child factors associated with weight trajectories will support future large scale longitudinal studies of risk and protective factors for maternal and child health. This research will also inform intervention targets facilitating healthy maternal and child weight

Sorting of EGF and transferrin at the plasma membrane and by cargo-specific signaling to EEA1-enriched endosomes

The biological function of receptors is determined by their appropriate trafficking through the endosomal pathway. Following internalization, the transferrin (Tf) receptor quantitatively recycles to the plasma membrane, whereas the epidermal growth factor (EGF) receptor undergoes degradation. To determine how Tf and EGF engage these two different pathways we imaged their binding and early endocytic pathway in live cells using total internal reflection fluorescence microscopy (TIRF-M). We find that EGF and Tf bind to distinct plasma membrane regions and are incorporated into different endocytic vesicles. After internalization, both EGF-enriched and Tf-enriched vesicles interact with endosomes containing early endosome antigen 1 (EEA1). EGF is incorporated and retained in these endosomes, while Tf-containing vesicles rapidly dissociate and move to a juxtanuclear compartment. Endocytic vesicles carrying EGF recruit more Rab5 GTPase than those carrying Tf, which, by strengthening their association with EEA1-enriched endosomes, may provide a mechanism for the observed cargo-specific sorting. These results reveal pre-endocytic sorting of Tf and EGF, a specialized role for EEA1-enriched endosomes in EGF trafficking, and a potential mechanism for cargo-specified sorting of endocytic vesicles by these endosomes

The vascular endothelium of the adipose tissue gives rise to both white and brown fat cells

Adipose tissue expansion involves the enlargement of existing adipocytes, the differentiation of adipocyte progenitors, and the development of the supporting vascular network. Although some data suggest that the adipocyte progenitors reside in the vasculature of the adipose tissue, their identity is not completely clear [1,2]. Here we address the hypothesis that a population of adipocytes derives from an endothelial cell (EC) lineage. We performed a detailed morphological analysis in developing murine WAT and BAT in order to highlight the features of adipocyte precursors. In addition, we used the VE-Cadherin- Cre/R26R mouse model to address the relationship between vascular ECs and adipose cells development. This lineage tracing model allowed the identification of cells that express the EC gene VE-Cadherin at any point during differentiation. Finally, we analyzed capillary sprouts arising from human subcutaneous fat tissue to evaluate the hypothesis that ECs forming these structures possess the capacity to transform into adipocytes. Ultrastructural analysis of discrete areas of intense adipogenesis, that we designated vasculo-adipocytic islets, revealed the presence of rare endothelial-pericytic cells that could represent an intermediate developmental step between the EC and the preadipocyte stage. Lineage tracing experiments using the VE-cadherin promoter revealed the expression of reporter genes in ECs, preadipocytes and adipocytes in white and brown fat depots. Furthermore, capillary sprouts (which have predominantly EC characteristics) from human adipose tissue were found to express Zfp423, a recently identified marker of preadipocyte determination [3]. In response to PPARγ activation the ECs lost progressively their structural and molecular characteristics, and formed structurally and biochemically defined adipocytes. We report morphological and genetic evidence that adipocytes in white and brown fat depots originate from cells that display endothelial characteristics and this is in accordance with the results published by other researchers [4] and also with previous works performed in our lab [5]