2. Metabolic Immunology
Also referred to as: Immunometabolism
Pathogenic defence is necessary for survival
The bodies immune response involves key changes to metabolic processes
Immune mediators, such as cytokines, also dictate changes in metabolism
Including, the endocrine regulation of substrate utilisation (Schertzer et al.,
2014)
Research has provided insight into:
How inflammation drives type 2 diabetes
How adipose-tissue-derived mediators are involved in inflammation and
metabolic disease
How immune cells act in adipose tissue
How T-cell metabolism is related to T-cell fate
Immunomodulatory strategies (Mathis et al., 2011).
3. Basic Role of Metabolism in the Immune System
Cell-intrinsic metabolic processes effect the performance of immune cells
Important in the control of immune cell number and function
Immune cells use and respond to nutrients just like other cells
Metabolic states depend on energy levels.
Uncoupling proteins play an important role in immunoprivilege (Newell et al.,
2006)
Changes in metabolism (by oxidative stress or energy availability) will initiate
changes in immune recognition and the nature of immune responses (MacIver
et al., 2013).
Pattern recognition receptors (PRRs) can integrate nutrient- and pathogen- sensing
systems.
Inflammasomes are thus, key regulators of metabolic inflammation by working
4. Adipose Tissue and Adipokines
Adipokines are cytokines which are secreted by adipose tissue
Adipose tissue, otherwise known as fat, is the connective tissue composed of
adipocytes
Members include:
Leptin, Interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNFα)
Leptin is not appropriately considered an adipokine as they do not act on the
immune system (Raucci et al., 2013)
Proinflammatory
They are signalling molecules that assist immune responses and stimulate the
movement of cells towards specific sites of inflammation and infection.
6. Inflammasomes
“Inflammasomes are large intracellular multi-protein complexes that play a central role
in innate immunity. They are key signalling platforms that detect pathogenic
microorganisms and sterile stressors, and that activate the highly pro-inflammatory
cytokines interleukin-1β (IL-1β) and IL-18.” – Latz et al., 2013
Tsutsui et al., 2010
7. The NLRP3 inflammasome: IL-1β and IL-18 production
Inflammasomes contain a member of the NOD-like receptor (NLR) family, including
NLRP3 and IPAF
The NLR protein recruits the inflammasome-adaptor protein ASC
p10 and p20 caspase-1subunits assemble to form active caspase-1
heterotetramers
Once activated, caspase-1 promotes the maturation of the proinflammatory
cytokines interleukin (IL)-1β and IL-18 (Benetti et al., 2013)
Following the activation of NLRP3, cells secrete large amounts of pro-inflammatory
cytokines
Cells will usually undergo caspase-1-induced cell death, which is also known as
pyroptosis.
8. Obesity Activates The NLRP3 Inflammasome
Obesity predisposes individuals to an range of chronic IL-1β-mediated metabolic
diseases, including type 2 diabetes (T2D)
Obesity-induced inflammatory state has also been linked to the activation of adipose
tissue macrophages (ATMs) within adipose tissue (Vandanmagsar et al., 2011)
Gene-deficient mice fed a high fat diet showed a reduced caspase-1 activation and
pro-IL-1β expression in adipose tissue, and a loss of serum IL-18 production, when
compared to the wild-type mice (Nardo et al., 2011)
A danger signal for NLRP3 activation in obesity is the increased presence of the lipid
molecule ceramide (composed of sphingosides and fatty acids)
LPS-primed macrophages stimulated with ceramide therefore display NLRP3-
dependent caspase-1 activation and production of IL-1β
10. NLRP3 Mediated Type 2 Diabetes
In macrophages, exogenous danger
signals, such as an increase in
saturated fatty acids, activate NLRP3
and trigger IL-1β release (Lee et al.,
2012)
IL-1β deregulates insulin signalling,
which potentially leads to insulin
resistance in cells.
Increased expression of the NLRP3
inflammasome in ATMs during an obese
state is related to the activation of T
cells, including interferon (IFN-γ) in
adipose tissue, which stimulates
macrophage activation and systemic
inflammation (Shahzad et al., 2014).
(Yang et al., 2012)
13. References
Benetti, E., Chiaza, F., Patel, N.S.A. and Collino, M. (2013) The NLRP3 inflammasome as a novel player of the intercellular crosstalk in
metabolic disorder. Mediators of Inflammation. 2013: doi:10.1155/2013/678627
Choi, A.M.K. and Nakahira, K. (2011) Dampening insulin signalling by an NLRP3 ‘meta-flammasome’. Nature Immunology. 12: 379-380
Lee, H.M., Kim, J.J., Kim, H.J., Shong, M., Ku, B.J. and Jo, E.K (2012) Unregulated NLRP3 inflammasome activation in patients with type
2 diabetes. Diabetes. 62: 194-204
MacIver, N.J., Michalek, R.D. and Rathmell, J.C. (2013) Metabolic Regulation of T Lymphocytes. Annual Review of Immunology. 31: 259-
283
Mathis, D. and Shoelson, S.E. (2011) Immunometabolism: An emerging frontier. Nature Reviews Immunology. 11(2): 81
Nardo, D.D. and Latz, E. (NLRP3 inflammasomes link inflammation and metabolic disease. Trends in Immunology. 32(8): 373-379
Newell, M.K., Villalobos,-Menuey, E., Schweitzer, S.C., Harper, M.E. and Camley, R.E. (2006) Cellular metabolism as a basis for immune
privilege. Journal of Immune Based Therapies and Vaccines. 4(1): doi:10.1186/1476-8518-4-1
Raucci, R., Rusolo, F., Sharma, A., Colonna, G., Castello., G. and Costantini, S. (2013) Functional and structural features of the adipokine
family. Cytokine. 61(1): 1-14
R&D Systems (2013) Obesity-induced activation of the NLRP3 inflammasome promotes insulin resistance [online] Available from:
http://www.rndsystems.com/cb_detail_objectname_cb11i2_obesity_induced_activation_nlrp3.aspx [Accessed 25th November 2014]
Schertzer, J.D. and Steinberg, G.R. (2014) Immunometabolism: The interface of immune and metabolic responses in disease.
Immunology and Cell Biology. 92: 303
Shahzad, K., Bock, F., Dong, W., Wang, H., Kopf, S., and Kohli, S. (2014) NLRP3-inflammasome activation in non-myeloid-derived cells
aggravates diabetic nephropathy. Kidney International. 2014: doi:10.1038/ki.2014.271
Trayhurn, P., Bing, C. and Wood, I.S. (2006) adipose tissue and adipokines – energy regulation from the human perspective. The journal
of nutrition. 136(7):19355-19395
Tsutsui, H., Imamura, m., Fujimoto, J. and Nakanishi, K. (2010) The TLR4/TRIF-mediated activation of NLRP3 inflammasome underlies
endotoxin-induced livery injury in mice. Gastroenterology Research and Practice. 2010: doi:10.1155/2010/641865
Vandanmagsar, B., Youm, Y.H., Ravussin, A., Galgani, J.E. and Stadler, K. (2011) The NLRP3 inflammasome instigates obesity-induced
inflammation and insulin resistance. Nature Medicine. 17: 179-188
Yang, C.S., Shin, D.M. and Jo, E.K. (2012) The role of NLR-related protein 3 inflammasome in host defence and inflammatory diseases.
International Neurology Journal. 16(1): 2-12
Hi, so I’m going to be talking about metabolic immunology today. I’ll give a brief overview of what it is, what is involved and the metabolic disorders linked to this topic.
Metabolic immunology is simply metabolism and immunology brought together as a diagnostic marker for obesity-related metabolic disorders. It should be noted, this is not just used in obesity cases, but most research has a found a significant link between the two.
As pathogenic defence is necessary for survival, our immune system sometimes relies on changes of metabolic processes, such as insulin secretion, to dictate a viable response. Take autoimmune disorders for instance, many often show characteristics of metabolic changes, which result in inflammation. Rheumatoid arthritis is a really great example of this, where the joints become highly inflamed, reducing dexterity and movement – this is usually the result of:
Metabolic changes, such as increased total cholesterol, LDL cholesterol and triglyceride levels, occur even in preclinical RA. Active RA is associated with decreased lipid levels, BMI, fat and muscle mass, as well as altered lipid profiles.
So, moving away from specifics, metabolic immunology, is surprisingly quite a new topic area, with research in the past 5 years providing insight into: (…)
Some of these I will talk about in more detail later on.
Cell-intrinsic metabolic processes can effect the performance of immune cells. During processes such as intrinsic regulation, metabolic pathways respond to changes in substrate levels. For example, when oxygen levels in tissues decline, cells release chemicals that dilate blood vessels. The dilation increases the rate of blood flow and provides more oxygen to region of interest. Recent studies have actually indicated that metabolic changes within tissues, are sometimes the result from the recruitment of inflammatory cells, such as neutrophils, monocytes and lymphocyte proliferation; thus, suggesting immune cells respond to nutrients just like other cell types.
Ultimately, metabolic states therefore depend on energy levels. Again, if linked to obesity-related issues, uncoupling proteins involved in the burning of fat, are seen to protect against free radicals, which is important in immunoprivilege. Changes in metabolism (by oxidative stress or energy availability) will thus initiate changes in immune recognition and the nature of immune responses. I will go onto talk about this in more detail later.
It is Inflammasomes which are the key regulators of metabolic inflammation by working as metabolic danger sensors.
So, metabolic disorders linked to immune responses, often dictate an increase in adipokines within adipose tissue. Adipokines simply, are immune cytokines that are involved in cell signaling. Members include: Leptin, Interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNFα). IL-6 for example, is highly involved in the inflammation found in various types of cancer and is a key mediator of insulin resistance – which highly effects glucose and lipid metabolism.
Ultimately, they are signalling molecules that assist immune responses and stimulate the movement of cells towards specific sites of inflammation and infection.
Also mediates immune responses to endogenous danger signals, including those arising in metabolic dysfunction. The potent proinflammatory cytokine, interleukin (IL)-1β, is known to contribute to the inflammatory response in various metabolic diseases.
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So, an increased level of an adipokine, such as Visfatin within fatty tissue, is linked to the activation of protein complexes known as Inflammasomes.
The inflammasome I will be focusing on, is the NLRP3.
Obesity-induced insulin resistance and dysfunction of islet β cells in the pancreas are characteristic of the disease
Stimulation of primed bone-marrow-derived DCs and macrophages with human IAPP was shown to induce cleavage of caspase-1, formation of ASC specks, and production of IL-1β in an NLRP3-dependent manner
The IL-1-induced inflammation produced in the pancreas probably results in death of β cells, T2D disease progression, and development of insulin-dependent diabetes.