Browsing by Subject "Glucose metabolism"

It has been long known that many types of cancers have high metabolic requirements and use reprogrammed metabolism to support cellular activities. The first identified metabolic alteration in cancer cells was elevated glucose uptake, glycolysis activity and lactate production even in the presence of oxygen. This metabolic program, termed aerobic glycolysis or the Warburg effect, provides cells with energy as well as biosynthetic substrates to sustain cell survival and rapid cell proliferation. Cancer metabolism is closely linked to genetic mutations and oncogenic signaling pathways, such as PI3K/Akt, cMyc and HIF pathways. These oncogenic signals can direct metabolic reprogramming while changes in metabolic status can regulate activities of these signaling pathways in turn. In addition to glucose, later studies also found utilization of alternate nutrients in cancer cells, including glutamine and lipids. Glutamine is the second major metabolic fuel and can be converted to various substrates to support cell bioenergetics needs and biosynthetic reactions. Usage of metabolic fuels in cancer cells, however, is variable. While certain cancers display addiction to one type of nutrient, others are capable of using multiple nutrients.

The unique metabolic features of cancer cells raise the possibility of targeting metabolism as a novel therapeutic approach for cancer treatment. Using pharmacological inhibitors, previous research has provided corroborating evidence that metabolic stress can impact survival and growth of proliferative cancer cells by regulating cell apoptotic machinery and cell cycle checkpoints. Due to lack of genetic tools and side effects from these inhibitors, however, mechanistic understanding of cell response to metabolic inhibition was limited in these studies. More importantly, how metabolic stress affects cancer progression in a physiological condition has not yet been well investigated. Lastly, current research has not examined metabolic program in indolent cancers and the metabolic requirements and activities in less proliferative cells also remain to be understood.

This work examines nutrients utilization in B cell derived acute and chronic leukemia (B-ALL and B-CLL). B-ALL is an aggressive form of leukemia. Using cell lines and primary patient samples, we found B-ALL cells primarily used glucose through aerobic glycolysis, similar to other proliferative cancer cells. B-ALL cells were also more sensitive to inhibition of glycolysis than normal B cells. Employing an untargeted metabolomics profiling in combination with isotope labeled glucose tracing approach, we show in a B-ALL model that genetic ablation of glucose transporter Glut1 partially reduced glucose uptake, sufficiently hindered anabolic pathways and promoted catabolic metabolism. This metabolic shift led to sharply curtailed B-ALL proliferation in vitro and reduced leukemic burden in vivo. Furthermore, this partial inhibition of glucose metabolism sensitized B-ALL cells to apoptotic stimuli and non-cytotoxic metabolic inhibition significantly enhanced efficacy of a tyrosine kinase inhibitor to eliminate B-ALL cells in vitro and in vivo. Thus, partial inhibition of glucose metabolism can provide a plausible adjuvant therapy to treat cancers that depend on glycolysis for survival and proliferation.

In contrast to B-ALL, B-CLL is an indolent form of cancer. Most B-CLL cells exhibited low glucose metabolic activities that were comparable with normal B cells at resting stage. Similar to chronically stimulated and anergic B cells, these B-CLL cells also failed to upregulate glucose metabolism in response to IgM stimulation. We also observed an altered amino acid and acyl-carnitine profile and increased glutaminase mRNA in B-CLL relative to normal B cells, suggesting the capability of using alternate nutrients such as glutamine in these cells. Finally, we explored the possibility of suppressing mitochondria metabolism to induce B-CLL cell death through inhibition of the nuclear hormone receptor and metabolic regulator ERRalpha. ERRalpha is known to regulate mitochondrial metabolism and was expressed higher in B-CLL than normal B cells. ERRalpha inhibition decreased viability of oncogene transformed pro-B cells, suggesting ERRalpha as a potential target for B-CLL treatment.

Collectively, this work investigates metabolic phenotype in two forms of leukemia derived from B cells. It reveals different metabolic requirements and activities in aggressive and indolent leukemia and explores different approaches to suppress metabolism in these cancers. Findings of this work shed light on how to potentially design metabolic approach to improve cancer treatment.

Understanding the mechanisms that control T cell function and differentiation is crucial to develop new strategies to modulate immune function and prevent autoimmune and inflammatory disease. The balance between effector (Teff; Th1, Th2 and Th17) and regulatory (Treg) T cells is critical to provide an appropriate, but not excessive, immune response and therapies to induce Treg or inhibit Teff are likely promising treatment strategies. It has recently become clear that T cell metabolism is important in both T cell activation and differentiation. T cells undergo a metabolic reprogramming upon activation and not all differentiated T cell subsets utilize the same metabolic fuels or programs.

These metabolic differences are not trivial, as T cell metabolism is tightly

regulated and dysregulation can lead to cell death or reduced immunity. An

understanding of the metabolic differences between Teff and Treg may lead to a new direction for treating inflammatory diseases by modulating the Teff:Treg balance through metabolic inhibition. Previous studies have shown that Teff express higher levels of the glucose transporter Glut1 than Treg, however the role of Glut1, and importantly, the cell-intrinsic role of glucose metabolism in T cell differentiation and inflammation was not previously examined. The work presented here examines the role of Glut1 in T cell differentiation. We show that effector CD4 T cells were dependent on Glut1 for proliferation and function both in vitro and in vivo. In contrast, Treg were Glut1-independent and capable of suppressing colitis in the absence of Glut1 expression.

Additionally, previous studies have shown broad metabolic differences between Teff and Treg, however the specific metabolic profiles of Teff and Treg are poorly understood. Here, Teff and Treg metabolism is examined to test if dependence on distinct metabolic pathways will allow selective targeting of different T cell populations. We show that pyruvate dehydrogenase kinase 1 (PDHK1) is differentially expressed in the T cell subsets and inhibition of PDHK1 selectively suppresses Th17 and promotes Treg differentiation and function. Because Teff and Treg have distinct metabolic profiles, we hypothesized that the Treg-­specific transcription factor FoxP3 may drive the Treg oxidative metabolic program. We therefore examined the role of FoxP3 in T cell metabolism and determined that FoxP3 promotes glucose and lipid oxidation and suppresses glycolytic metabolism. Importantly, we show that promoting glycolysis with transgenic expression of Glut1 inhibits Treg suppressive capacity. Together, these data suggest that FoxP3 drives an oxidative metabolic program that is critical to Treg function. Overall, this work examines the metabolic phenotypes and regulation of Teff and Treg and potential metabolic targets that could be used to treat autoimmune and inflammatory disease.

Basement membranes (BM) are dense, highly crosslinked sheets of extracellular matrix proteins that surround and constrain cells in animal tissues. Specialized cells acquire the ability to invade through BM barriers during development and homeostasis, and aberrant BM invasion underlies many diseases. Invading cells use transient and specialized cellular protrusions to breach the BM, and the membrane dynamics and cytoskeletal rearrangements necessary to build and fuel these structures are both energy intensive and metabolically complex. Thus, it is crucial to understand how invasive cells regulate their catabolic and anabolic metabolism to drive BM invasion, but experimentally dissecting stochastic cell invasion events that occur deep within optically inaccessible tissues in vivo is challenging. Here I use the C. elegans anchor cell (AC) as an experimentally tractable and visually accessible in vivo model for cell invasion through the BM, and use 4D live cell imaging , metabolic biosensors, and RNAi-mediated screening to investigate how invading cells regulate their ATP production and lipid metabolism to drive invasion through the BM. In Chapter 1, I review the mechanisms used by cells to fuel invasion through matrix and identify gaps in our understanding of localized energy production during invasion. In Chapter 2, I discover that localized glucose import, and glycolytic processing support rapid and transient ATP production by mitochondria in the AC to fuel the invasive protrusions for BM invasion. In Chapter 3, I identify that sphingolipid biogenesis and protein prenylation support the formation of the invasive protrusion and the actin-based invasion machinery within in to breach the BM barrier. In Chapter 4, I discuss the implications of these findings on our understanding of the metabolism of cells invading through the BM.