Azidotetrakis(trimethylphosphine)nickel(II) Tetrafluoroborate

The title complex, [Ni(N3)(C3H9P)4]BF4, is a nearly perfect trigonal bipyramid with the azide group at an apical position. The metal-azide bond angle, Nil-- NlmN2, of 138.6(5) ° is the largest observed for a terminal azide ligand

The Good, The Brown, and The Healthy: Understanding Non-Thermogenic Brown Adipose Function in Obese Mice

Genetic and environmental factors heavily intertwine to affect metabolic homeostasis. To tease out the exact interactions between these two realms of influence, researchers often compare how one or multiple different inbred mouse strains react to various diets. An observation consistently seen across multiple strains on the same diet can reasonably be considered a general dietary effect, whereas an observation seen only in one strain of mice is more likely to result from a genetic cause or gene-by-environment interaction. Similarly to humans, a high fat diet causes many mouse strains to develop obesity and poor metabolic health, with varying degrees of hyperglycemia, hyperinsulinemia, systemic insulin resistance, hyperlipidemia, ectopic lipid deposition, and inflammation and dysfunction of metabolic tissues. The LG/J and SM/J inbred mouse strains show disparate responses to long-term exposure to a high fat diet. While 20 weeks of high fat diet causes both strains to develop obesity, hyperglycemia and impaired glucose tolerance, the glycemic effect in SM/J mice is stronger than in LG/J mice, and SM/J mice also develop hyperinsulinemia and impaired insulin sensitivity. Interestingly, an additional 10 weeks of high fat diet exposure results in reversion of unhealthy glycemic levels in SM/J mice, while LG/J mice maintain their elevated glucose parameters. This diabetic remission in SM/J mice is not the result of weight loss; the mice continue to gain weight, and in particular show a dramatic increase in the mass of their interscapular brown adipose tissue. Brown adipose tissue is best known for its function in non-shivering thermogenesis, the release of energy in the form of heat, however it has also emerged as a potent source of cytokines that can coordinate whole-body metabolic homeostasis. Based on the concurrent timing of the two phenomena, I hypothesized that the expansion of brown adipose tissue in the high fat-fed SM/J mice directly contributes to the glycemic normalization through secretion of pro-health cytokines and by serving as a more efficient glucose sink. Though brown adipose is primarily associated with metabolic improvement through thermogenic action, I found no evidence that the expansion of brown adipose tissue in high fat-fed SM/J mice leads to increased thermogenesis. There is no change in the expression of the thermogenic genes Ucp1, Cidea, and Eva1, nor is there any change in mitochondrial DNA content, brown adipocyte morphology and Ucp1 staining, core body temperature, or circulating levels of thermogenesis-activating catecholamines. Instead, I found that the expression levels of Irs1 and Glut4, two key members of the insulin-stimulated glucose uptake pathway, increase significantly with the brown adipose expansion. This suggested that the brown adipose expansion can act as a insulin-responsive sink for excess blood glucose, and indeed removal of the brown adipose depot before or after expansion prevents the improvement in whole-body insulin sensitivity. To further explore the gene-by-environment interactions that cause the uniqueness of the SM/J brown adipose expansion and its association with metabolically healthy obesity, I analyzed the transcriptomic profile of the brown and white adipose tissues of high and low fat-fed LG/J and SM/J mice at 20 and 30 weeks. I performed weighted gene co-expression network analysis to identify clusters of genes whose expression in brown adipose tissue correlate with metabolic phenotypes. I identified four clusters that are enriched for genes in cell division, immune and cytokine response, organic molecule metabolism, and peroxisome function, as well as four clusters that have no significant enrichment. While other modules were identified in all cohorts, the cell division cluster was only found when the high fat-fed SM/J mice were included in the analysis. Principal components analysis of the expression of genes in this cluster shows a distinct grouping of the high fat-fed SM/J samples away from the other cohorts. Twenty-nine genes in the cell division cluster also show significant differential expression between 20 and 30 weeks in high fat-fed SM/J brown adipose. In particular, expression of Sfrp1 (secreted frizzled-related protein 1) positively correlates with brown adipose mass across all SM/J cohorts and with improved glucose tolerance in the high fat-fed SM/J mice. Sfrp1 has previously been identified as a pro-adipogenic cytokine in white adipose that positively correlates with insulin sensitivity and declines in obesity. The Sfrp1 locus contains variants between LG/J and SM/J mice and is located within QTL for adiposity and glucose tolerance. The human SFRP1 genomic region contains a variant (rs973441) is significantly associated with type 2 diabetes adjusted for BMI. Overall, my dissertation robustly characterizes a novel mouse model of insulin-sensitive obesity dependent on natural brown adipose tissue expansion. I have defined the first brown adipose gene co-expression clusters and their relationship to metabolic phenotypes and identified the cytokine Sfrp1 as a novel stimulator of brown adipogenesis and insulin sensitivity. Together, these studies expand our knowledge of the potent non-thermogenic ability of brown adipose tissue to promote healthy metabolism in an obese state

Identification of the Roles of the Small Ubiquitin-Related Modifier (SUMO) in Cellular Stress Response

Proper protein folding is essential for cell function, as misfolding leads to cell stress and cytotoxicity. Misfolded proteins are associated with several serious diseases in humans such as Parkinson’s and Alzheimer’s diseases. The posttranslational modifier SUMO has been implicated in several of these diseases, including cystic fibrosis, amyotrophic lateral sclerosis, and other neurodegenerative diseases. However, the mechanism by which SUMO affects protein folding and stress response is not well understood. To address this question, we investigated a SUMO mutant that is sensitive to canavanine, an arginine analog that induces protein misfolding. We characterized this mutant as deficient in binding to proteins containing SUMO-interacting motifs (SIMs) and hypothesized that a high-copy suppressor screen would identify proteins that function downstream of SUMO in the protein stress response. We found that San1, a ubiquitin E3 ligase involved in nuclear protein quality control, can suppress the sensitivity of our mutant to canavanine. Interestingly, the RING domain required for E3 ligase activity is not necessary for suppression, but the unstructured N-terminus of San1 is both necessary and sufficient for suppression. The N-terminus has a chaperone-like function, binding to unstructured, misfolded proteins. Our findings suggest that sumoylation may either play a similar role and promote proper protein folding, or function to prevent the accumulation of toxic misfolded proteins in the cell

Brown adipose expansion and remission of glycemic dysfunction in obese SM/J mice

We leverage the SM/J mouse to understand glycemic control in obesity. High-fat-fed SM/J mice initially develop poor glucose homeostasis relative to controls. Strikingly, their glycemic dysfunction resolves by 30 weeks of age despite persistent obesity. The mice dramatically expand their brown adipose depots as they resolve glycemic dysfunction. This occurs naturally and spontaneously on a high-fat diet, with no temperature or genetic manipulation. Removal of the brown adipose depot impairs insulin sensitivity, indicating that the expanded tissue is functioning as an insulin-stimulated glucose sink. We describe morphological, physiological, and transcriptomic changes that occur during the brown adipose expansion and remission of glycemic dysfunction, and focus on Sfrp1 (secreted frizzled-related protein 1) as a compelling candidate that may underlie this phenomenon. Understanding how the expanded brown adipose contributes to glycemic control in SM/J mice will open the door for innovative therapies aimed at improving metabolic complications in obesity

Spontaneous restoration of functional β-cell mass in obese SM/J mice

Maintenance of functional β-cell mass is critical to preventing diabetes, but the physiological mechanisms that cause β-cell populations to thrive or fail in the context of obesity are unknown. High fat-fed SM/J mice spontaneously transition from hyperglycemic-obese to normoglycemic-obese with age, providing a unique opportunity to study β-cell adaptation. Here, we characterize insulin homeostasis, islet morphology, and β-cell function during SM/J\u27s diabetic remission. As they resolve hyperglycemia, obese SM/J mice dramatically increase circulating and pancreatic insulin levels while improving insulin sensitivity. Immunostaining of pancreatic sections reveals that obese SM/J mice selectively increase β-cell mass but not α-cell mass. Obese SM/J mice do not show elevated β-cell mitotic index, but rather elevated α-cell mitotic index. Functional assessment of isolated islets reveals that obese SM/J mice increase glucose-stimulated insulin secretion, decrease basal insulin secretion, and increase islet insulin content. These results establish that β-cell mass expansion and improved β-cell function underlie the resolution of hyperglycemia, indicating that obese SM/J mice are a valuable tool for exploring how functional β-cell mass can be recovered in the context of obesity

Parent-of-origin effects propagate through networks to shape metabolic traits

Parent-of-origin effects are unexpectedly common in complex traits, including metabolic and neurological traits. Parent-of-origin effects can be modified by the environment, but the architecture of these gene-by-environmental effects on phenotypes remains to be unraveled. Previously, quantitative trait loci (QTL) showing context-specific parent-of-origin effects on metabolic traits were mapped in the

Understanding the Role of Past Health Care Discrimination in Help-Seeking and Shared Decision-Making for Depression Treatment Preferences

As a part of a larger, mixed-methods research study, we conducted semi-structured interviews with 21 adults with depressive symptoms to understand the role that past health care discrimination plays in shaping help-seeking for depression treatment and receiving preferred treatment modalities. We recruited to achieve heterogeneity of racial/ethnic backgrounds and history of health care discrimination in our participant sample. Participants were Hispanic/Latino (n = 4), non-Hispanic/Latino Black (n = 8), or non-Hispanic/Latino White (n = 9). Twelve reported health care discrimination due to race/ethnicity, language, perceived social class, and/or mental health diagnosis. Health care discrimination exacerbated barriers to initiating and continuing depression treatment among patients from diverse backgrounds or with stigmatized mental health conditions. Treatment preferences emerged as fluid and shaped by shared decisions made within a trustworthy patient–provider relationship. However, patients who had experienced health care discrimination faced greater challenges to forming trusting relationships with providers and thus engaging in shared decision-making processes

A high throughput mutagenic analysis of yeast sumo structure and function

<div><p>Sumoylation regulates a wide range of essential cellular functions through diverse mechanisms that remain to be fully understood. Using <i>S</i>. <i>cerevisiae</i>, a model organism with a single essential SUMO gene (<i>SMT3</i>), we developed a library of >250 mutant strains with single or multiple amino acid substitutions of surface or core residues in the Smt3 protein. By screening this library using plate-based assays, we have generated a comprehensive structure-function based map of Smt3, revealing essential amino acid residues and residues critical for function under a variety of genotoxic and proteotoxic stress conditions. Functionally important residues mapped to surfaces affecting Smt3 precursor processing and deconjugation from protein substrates, covalent conjugation to protein substrates, and non-covalent interactions with E3 ligases and downstream effector proteins containing SUMO-interacting motifs. Lysine residues potentially involved in formation of polymeric chains were also investigated, revealing critical roles for polymeric chains, but redundancy in specific chain linkages. Collectively, our findings provide important insights into the molecular basis of signaling through sumoylation. Moreover, the library of Smt3 mutants represents a valuable resource for further exploring the functions of sumoylation in cellular stress response and other SUMO-dependent pathways.</p></div