PI: Michael B. Brenner, M.D
Abstract:Inflammation in adipose tissue plays a critical role in obesity, the metabolic syndrome and Type 2 Diabetes.
Recently, changes in the number and function of invariant (i) NKT cells have been implicated. In non-obese people, iNKT cells are present in omenta adipose tissue at higher levels than anywhere else in the body and they are similarly enriched in epididymal adipose tissue in mice. iNKT cells in adipose tissue display an anti-inflammatory cytokine phenotype producing IL-10 rather than the INFγ phenotype noted in other tissues. iNKT cell deficient mice on a high fat diet had enhanced weight gain, fatty livers and insulin resistance that was reversed upon adoptive transfer of iNKT cells. These studies point to a striking role for iNKT cells in obesity, glucose intolerance, and fatty liver changes in mice and humans.
iNKT cells are innate T cells that express an invariant T cell receptor, have an effector/memory phenotype and secrete massive amounts of cytokines rapidly after stimulation. Unlike MHC restricted T cells, iNKT cells are CD1d-restricted and recognize lipid antigens. Recently, we identified the major lipid self-antigens responsible for iNKT cell activation as β-linked glucosylceramides, the precursors for synthesis of complex glycosphingolipids. Regulation of lipid biosynthesis following inflammatory stimuli dramatically altered the levels of the potent stimulatory β-linked ceramide lipid antigens and controlled iNKT cell activation. Our preliminary data suggests that the adipose tissue iNKT cell antigens are different from the β-ceramide lipid self-antigens we identified in other tissues, since the adipose tissue antigens are found in the non-polar lipid fraction of extracts compared to the other tissue antigens which are polar ceramide lipids.
Here, we will perform biochemical purifications like those we used to identify the main lipid self-antigens that activate iNKT cells in infection, but now to identify the lipid self-antigens in adipose tissue that are responsible for iNKT cell activation in lean compared to obese states. First in Aim I, we will determine the lipid self-antigens in adipose tissue found in normal mice that activate iNKT cells to produce IL-10. Then in Aim 2, we will feed mice a high fat diet with fat from mammalian or vegetable sources to determine how the fat source alters the pool of antigenic lipids in adipose tissue. Finally, in Aim 3 we will administer the lipids identified that stimulate iNKT cell IL-10 production (from Aim 1) to mice on a high fat diet as a potential therapeutic focused on iNKT cell modulation of adipose inflammation. Together, these studies will provide new insights into the role of lipids as auto-antigens that alter the function of iNKT cells relevant to regulating inflammation in obesity and Type II Diabetes.
PI: Florian Eichler, M.D.
Abstract:Deoxysphingoid Lipids in Diabetes and Diabetic Polyneuropathy
Background: Diabetes is the leading cause of neuropathy in the developed world and neuropathy is the most common complication and greatest source of morbidity and mortality in diabetes patients (WHO 2009). We recently discovered the accumulation of deoxysphingoid lipids (dSL) in an inherited polyneuropathy (HSN1, hereditary sensory neuropathy type 1) with features very similar to that of diabetic polyneuropathy. In the inherited disorder, the enzyme serine palmitoyl-transferase (SPT) loses affinity for serine and takes up other amino acids, such as alanine. This results in the formation of an atypical class of lipids (dSL) that have been shown to be toxic. Recently we also found these dSL elevated in patients with diabetes (Bertea et al. 2010), thereby elucidating a common pathway in the degeneration of peripheral nerve.
Methods: For this pilot study we have 3 goals: (1) measure plasma dSL in different forms of diabetes (type 1 versus type 2), (2) define the association between plasma dSL and the level of glycemic control over time, and (3) examine the correlation between plasma dSL and the severity of neuropathy, as measured by the Diabetes Neuropathy Scale and nerve conduction studies. Studies will be performed on a retrospective cohort of 50 diabetic patients seen at the MGH Diabetes Research Unit. A subset of these patients has been seen at the MGH Neuromuscular Center and received nerve conduction studies. Total lipids will be examined from previously collected and stored plasma and extracted according to the previously published methods (Riley et al. 1999).
Innovation and Significance: Our study will provide a first description of the association between dSL, level of glycemic control, and severity of neuropathy in diabetes. Our proposal will generate new insight into the molecular and metabolic aspects of diabetes and the peripheral nerve, and offers the opportunity for developing novel treatment for diabetic polyneuropathy. Using L-serine, we were able to lower dSL in both mice and humans with HSN1 (Garofalo et al. Journal of Clinical Investigation in press). We expect that similar progress could be made for the diabetic polyneuropathy and lead to pilot data that we can use for a R01 application.
Bertea, M., Rutti, M.F., Othman, A., Marti-Jaun, J., Hersberger, M., von Eckardstein, A., and Hornemann, T. Lipids Health Dis 9:84.
Garofalo K, Penno A, Schmidt BP, Lee H, Frosch MP, von Eckardstein A, Brown RH, Hornemann T, Eicher FS. Journal of Clinical Investigation in press. 2011.
Riley, R. T., Norred, W. P., Wang, E., and Merrill, A. H. (1999) Nat Toxins 7, 407-414
PI: Natalie D. Shaw, MD
Abstract: Short sleep duration is known to be detrimental to multiple endocrine axes in adults
Recent studies have cautioned that disturbances in normal sleep architecture may also lead to a deterioration in glucose tolerance and increase the risk of type 2 diabetes even when the total sleep duration is normal. A study by Tasali et. al. demonstrated that despite sleeping for the recommended 8 hours per night, adults deprived only of slow-wave sleep (SWS) suffered from a 25% decrease in insulin sensitivity the next morning, suggesting that nocturnal SWS plays a critical role in glucose homeostasis during both sleep and wakefulness.
SWS deprivation is likely to have an even greater effect on insulin sensitivity in pubertal children who are relatively insulin resistant at baseline secondary to the pubertal increase in growth hormone secretion. In addition, beginning at age 11-12 years in normal children, there is a steep decline in the time spent in SWS which continues through late adolescence. Given the high, and increasing, incidence of sleep deprivation among adolescents, it is important to determine the effects of SWS deprivation on insulin resistance in this vulnerable population so that appropriate interventions to restore SWS can be implemented.
The current proposal will address the question of whether a single night of SWS deprivation decreases insulin sensitivity using a mixed meal tolerance test in healthy pubertal children.
PI: Alex Soukas, MD, Ph.D.
Abstract: A great paradox in type 2 diabetes mellitus is preserved hepatic sensitivity to the stimulatory action of insulin on lipogenesis, despite resistance to the glucose-lowering effects of insulin. This frequently leads hepatic steatosis and hypertriglyceridemia to accompany poor glycemic control in type 2 diabetic patients. To study the molecular underpinning for this paradox, we generated mice lacking hepatic mammalian target of rapamycin complex 2 (mTORC2), an upstream activator of the protein kinase Akt, a critical regulator of hepatic glucose and lipid metabolism. Hepatic mTORC2 inactivation fails to activate Akt in response to insulin, producing increased hepatic glucose output and defective hepatic lipogenesis. Genetic approaches confirmed that the effects of mTORC2 knockout on glucose metabolism are due to loss of phosphorylation and activation of Akt. However, effects of mTORC2 on hepatic lipid metabolism could not be rescued by forced activation of Akt, indicating the existence of important targets of mTORC2 which act downstream of Akt that are essential for hepatic lipogenesis. We propose identification of these mTORC2 targets critical to insulin-stimulated hepatic lipogenesis. First, we will genetically re-activate mTORC1 and AGC kinases, which we have identified to be silenced in hepatic mTORC2 mutants,by in vivo adenoviral-mediated transduction in hepatic mTORC2 knockouts to determine involvement in hepatic lipogenesis. Second, we will study the effect of RNAi-based inactivation of mTORC2 target genes identified in our studies and in phosphoproteomic studies on lipogenesis in a hepatocyte cell model of TORC2 deficiency. Overall this pilot and feasibility proposal will illuminate signaling steps critical to insulin’s ability to stimulate hepatic lipogenesis. The ultimate goal is to further study genes involved in insulin-stimulated hepatic lipogeneis in vivo using transgenic and knockout mouse approaches in order to illuminate disease mechanisms of disordered lipid synthesis in human diabetes.
RELEVANCE: Type 2 diabetes is associated with high blood sugar and the development of a fatty liver in part due to changes in insulin action in the liver. Fatty liver in type 2 diabetes is associated with worsening of blood sugar control in and can in some cases lead to hepatitis or frank cirrhosis and liver failure. This research program will evaluate the potential role of target of rapamycin complex 2 and its downstream signaling events as new therapeutic targets in type 2 diabetes as we have found it has the ability to selectively regulate blood sugar and the development of a fatty liver in diabetes.