Psychosocial Stress, Inflammation, and Adhesion Molecules

I have been re-reading a book by Joseph LeDoux (NYU), Synaptic Self: How Our Brains Become Who We Are (2002), in which he argues that synapses in the brain are the foundation of personality, the basis of our sense of self:

My notion of personality is pretty simple: it‟s that your “self,” the essence of who you are, reflects patterns of interconnectivity between neurons in your brain. Connections between neurons, known as synapses, are the main channels of information flow and storage in the brain. Most of what the brain does is accomplished by synaptic transmission between neurons, and by calling upon the information encoded by past transmission across synapses. (p. 3-4)

This is relevant to some of the work I have been doing for Dr. Cress at the University of Arizona Cancer Center. Dr. Cress has been working for many years on the function of integrins in cancer metastasis, specifically in prostate cancer.

Here is how integrins are defined at Wikipedia, which is as precise as any you will find.

Integrins are transmembrane receptors that are the bridges for cell-cell and cell-extracellular matrix (ECM) interactions. When triggered, integrins in turn trigger chemical pathways to the interior (signal transduction), such as the chemical composition and mechanical status of the ECM, which results in a response (activation of transcription) such as regulation of the cell cycle, cell shape, and/or motility; or new receptors being added to the cell membrane. This allows rapid and flexible responses to events at the cell surface, for example to signal platelets to initiate an interaction with coagulation factors.

There are several types of integrins, and a cell may have several types on its surface. Integrins are found in all metazoa.^[3]

Integrins work alongside other receptors such as cadherins, the immunoglobulin superfamily cell adhesion molecules, selectins and syndecans to mediate cell–cell and cell–matrix interaction. Ligands for integrins include fibronectin, vitronectin, collagen, and laminin.

Integrins are heterdimic adhesion receptors, meaning they have two different parts, the α (alpha) and β (beta) subunits. There are at least 18 α and eight β subunits are known in humans and other vertebrates (Takada, Ye, & Simon, 2007).

Dr. Cress has been work with the A6B4 integrin (alpha 6 beta 4) and its role in metastatic prostate cancer. A6 is one of three laminin-binding molecules in humans (the others are A3 and A7), although other researchers suggest there are five laminin-binding integrins, A1, A2, A3, A6, A7 (Alberts, Johnson, & Lewis; 2007; Molecular Biology of the Cell. 5th edition). This graphic explains the functions of the different integrins and their combinations.

Integrins are also expressed in the brain, especially in synapses and in the lamination of axons, which allows information to more quickly and efficiently through the brain (and through neural cells throughout the body). Schwann cells in peripheral nerves interact with axons and extracellular matrix (ECM) as part of their work in ensheathing and myelinating axons and they express B4 (beta 4 integrin) [Feltri, et al, 1994], and specifically A6B4. 

In digging around for additional information on synapses and brain function, I found a related article by LeDoux - this is the abstract (crucial section is in bold):

STRUCTURAL PLASTICITY AND MEMORY
Raphael Lamprecht and Joseph LeDoux

Much evidence indicates that, after learning, memories are created by alterations in glutamate-dependent excitatory synaptic transmission. These modifications are then actively stabilized, over hours or days, by structural changes at postsynaptic sites on dendritic spines. The mechanisms of this structural plasticity are poorly understood, but recent findings are beginning to provide clues. The changes in synaptic transmission are initiated by elevations in intracellular calcium and consequent activation of second messenger signalling pathways in the postsynaptic neuron. These pathways involve intracellular kinases and GTPases, downstream from glutamate receptors, that regulate and coordinate both cytoskeletal and adhesion remodelling, leading to new synaptic connections. Rapid changes in cytoskeletal and adhesion molecules after learning contribute to short-term plasticity and memory, whereas later changes, which depend on de novo protein synthesis as well as the early modifications, seem to be required for the persistence of long-term memory.

Source: Nature Reviews Neuroscience; January 2004; 5(1):45-54. doi:10.1038/nrn1301 

Rho GTPaseas mediate extracellular stimulation-induced actin cytoskeleton rearrangements. Stimulation of the postsynaptic neuron leads to actin-dependent morphological changes mediated by Rho GTPases105–108. 1) Activation of adhesion molecules, such as integrin or cadherin, which have been shown to be involved in synaptic plasticity, regulates Rho GTPase inactivation by RhoGAPs. 2) Calcium influx through membrane channels can induce activation of tyrosine kinases (TKs), such as the cell adhesion kinase-β/proline-rich tyrosine kinase 2 (CAKβ/Pyk2), that in turn activate Src. The later modulates p190 RhoGAP activity and thereby controls Rho GTPase inactivation. 3) On the other hand, Rho GTPase activators, RhoGEFs, are also regulated by extracellular stimulation. Ephrin A activates, through the receptor tyrosine kinase EphA, a Rho GEF called ephexin. EphA has been implicated in memory formation133. 4) Rho GTPase controls actin polymerization through downstream effectors such as Rho-associated kinase (ROCK). ROCK activates LIM-domain-containing protein kinase (LIMK), which in turn inhibits the actin depolymerizing factor cofilin. This event can contribute to actin polymerization. ROCK, LIMK and cofilin have been shown to be involved in synaptic plasticity. 5) Cdc42 and Rac, other members of the Rho GTPase family, induce actin polymerization by regulating downstream effectors. GAP, GTPase-activating protein; GEF, guanine nucleotide exchange factor; N-WASP, neuronal Wiskott-Aldrich syndrome; SCAR, suppressor of cAR.

The text above is the caption for the image. Here is another quote from near the end of the paper, which is minimal and could be the topic of an entire paper:

Adhesion molecules and synaptic plasticity 

The formation of new synaptic contacts is a dynamic process that involves ongoing morphological alterations and modulation of adhesion between the pre- and postsynaptic neurons [115,116]. These processes require coordinated activity between molecules that regulate cytoskeletal rearrangements and morphology, and those that control adhesion between the pre- and postsynaptic membranes.Adhesion molecules, mostly integrins, cadherins, neurexin and the immunoglobulin superfamily, are membrane-bound molecules that have hetero- or homophilic interactions with proteins in the extracellular matrix and synaptic membranes to control the adhesion between the pre- and postsynaptic membranes. Adhesion molecules, which also have an intracellular component, can initiate signalling pathways that couple the dynamics of extracellular connectivity with intracellular events that control morphology. For example, cadherin regulates dendritic spine morphogenesis and function. Blockade of cadherin function leads to elongation of the spine, bifurcation of its head structure and alterations in the distribution of postsynaptic proteins [117]. Moreover, neuronal activity induces the movement of β-catenin (which mediates the interaction of cadherin with the actin cytoskeleton) from dendritic shafts into spines to become associated with cadherin and to influence synaptic size and strength [118]. Adhesion molecules such as cadherin also associate with molecules that regulate cytoskeletal rearrangements, such as proteins that control the Rho GTPase pathway [119].

Adhesion molecules could therefore contribute to the morphological alteration and stabilization of connectivity between neurons, a process that is hypothesized to underlie memory consolidation. Consistent with this hypothesis is the role of adhesion molecules in the formation and stabilization of LTP and LTM. Integrin-mediated adhesion helps to stabilize early-phase LTP (E-LTP) into late-phase LTP (L-LTP). For example, inhibition of integrin with a peptide that contains the integrin recognition sequence 10 min before, immediately after and 10 min after LTP induction caused a gradual decay of synaptic strength over 40 min [120]. The peptide had no effect when applied 25 min after LTP initiation, indicating that integrin has a role in stabilization of synaptic connectivity. Furthermore, N-cadherin is synthesized and internalized to new assembled synapses during the induction of L-LTP, and blocking N-cadherin adhesion prevents the induction of L-LTP but not E-LTP [121]. This event depends on glutamate receptor activity. In chicks, memory is impaired 24 h after a visual categorization task when antibodies against the cell adhesion molecule L1 are injected before, 5.5 h or 15–18 h after training (but not later) [122]. In addition, intraventricular injection of antibodies against neural cell adhesion molecule (NCAM) in rats 6–8 h after passive avoidance training, but not later, impaired retention of the avoidance response [123]. These observations indicate that adhesion molecules are essential for memory consolidation during a period of hours after acquisition.

The level and distribution of adhesion molecules is also correlated with synaptic plasticity and learning. In Aplysia, repeated application of 5-hydroxytryptamine (serotonin; 5-HT), which leads to long-term facilitation of the sensory–motor connection, induces the internalization of the adhesion molecule apCAM (Aplysia cell adhesion molecule) [43]. This could destabilize the interaction between sensory neurons, permitting the growth of new sensory axons.ApCAM could be redistributed to the area where new synapses are formed. In rats, N-cadherin is induced in the piriform cortex and hypothalamus 2 h after fear conditioning [124]. N-cadherin was not induced in control animals that were presented with the conditioned stimulus and unconditioned stimulus in a non-associative manner.

On the whole, these observations indicate that adhesion molecules have a central role in mediating neuronal connectivity and morphogenesis, and in the progressive stabilization of synaptic connectivity that leads to memory consolidation. (LeDoux, 2004, pages 50-51)

I did some more digging and found that A3, A5, A8, and B1 (McGeachie, Cingolani, & Godaare, 2011) are all expressed in synaptic formation and function and in the growth and activity of dendrites. If the alpha versions of the integrins are not functioning properly, learning and memory are inhibited, but there are differences for each of the alpha integrins and for the beta integrin:

Interestingly, behavioural tests revealed specific deficits in hippocampal-dependent working memory, while spatial memory was unaffected. Although ITGβ1 is likely to be the major subunit for ITGα3, ITGα5 and ITGα8 in the hippocampus (Hynes, 2002), ITGα3/+;ITGα5/+;ITGα8/+ mice showed behavioural deficits (see above) that are different from those of ITGβ1 conditional knockout mice. Such divergent results may reflect the differences arising from global reduction in ITGα3, ITGα5 and ITGα8 versus a more specific ablation of ITGβ1 mainly in CA1 pyramidal neurons.

[In the quote above, ITGα3, and so on, is used to represent integrin (ITG) alpha 3.] 

Inflammation from Psychosocial Stress

We know that psychosocial stress causes inflammation. University of Arizona researcher/professor Charles Raison (2006) found that depressed patients have higher levels of proinflammatory cytokines, acute phase proteins, chemokines, and cellular adhesion molecules (an important finding for my thesis). It has also been shown that therapeutic administration of the cytokine interferon-α (a cancer treatment drug that inhibits tumor cell growth) leads to depression in up to 50% of patients (Bonaccorso, et al, 2002).

Stress appears to down-regulate immunity through at least three mechanisms:

(A) Stress hormones are influenced by negative events and negative emotions: catecholamines (adrenaline and noradrenaline), adrenocorticotropic hormone (ACTH), cortisol, growth hormone, and prolactin, as examples

(B) Immune modulation by these hormones proceeds through two pathways: 

1. Directly, through binding of the hormone to its cognate receptor at the surface of a cell 
2. Indirectly — for example, by inducing dysregulation of the production of cytokines, such as interferon-γ (IFN-γ), interleukin-1 (IL-1),IL-2,IL-6 and tumour-necrosis factor (TNF)

Cytokines such as IFN-γ have many functions and affect different target cells. Therefore, there are secondary effects of many stress hormones on the immune response

(C) Communication between the CNS and the immune system is bidirectional - examples: 

1. IL-1 influences the production of corticotropin-releasing hormone (CRH) by the hypothalamus. In turn, CRH can affect the HPA axis and thereby trigger increases in stress hormone levels, which results in dysregulation of immune function 
2. Lymphocytes can synthesize hormones such as ACTH, prolactin and growth hormone

Glaser, R., & Kiecolt-Glaser, J. K. (2005). Stress-induced immune dysfunction: implications for health. Nature Reviews Immunology, 5(3), 243-251.

Here is the abstract (edited for relevance) from an excellent review article: Psychosocial stress and inflammation in cancer by Powell, Tarr, and Sheridan (2013) that provides some useful information about how stress (i.e., trauma) can compromise the immune system. [Bold area is my emphasis.]

Stress-induced immune dysregulation results in significant health consequences for immune related disorders including viral infections, chronic autoimmune disease, and tumor growth and metastasis.  Both human and animal studies have shown the sympathetic and neuroendocrine responses to psychosocial stress significantly impacts cancer, in part, through regulation of inflammatory mediators. Psychosocial stressors stimulate neuroendocrine, sympathetic, and immune responses that result in the activation of the hypothalamic–pituitary–adrenal (HPA)-axis, sympathetic nervous system (SNS), and the subsequent regulation of inflammatory responses by immune cells. Social disruption (SDR) stress, a murine model of psychosocial stress and repeated social defeat, provides a novel and powerful tool to probe the mechanisms leading to stress-induced alterations in inflammation, tumor growth, progression, and metastasis.

The following is from the first section of the same paper and it provides an overview of the chemical pathways involved in stress-induced inflammation.

[S]tudies using a mouse model of repeated social defeat, termed social disruption (SDR) stress, have shown that stress alone can trigger the generation, egress, and trafficking of immature, inflammatory myeloid derived-cells that are glucocorticoid (GC) insensitive (Curry et al., 2010, Engler et al., 2004a and Engler et al., 2005). In addition, these GC insensitive cells produce high levels of IL-6 and other inflammatory cytokines and chemokines (Powell et al., 2009, Stark et al., 2002 and Wohleb et al., 2011). As a consequence, these stress-induced changes at the cellular level translate to significant immune (enhanced inflammatory responses and immunity to microbial, viral, and allergen challenge) and behavioral (prolonged anxiety-like behavior) changes (Bailey et al., 2007, Bailey et al., 2009b, Bailey et al., 2009a, Dong-Newsom et al., 2010, Kinsey et al., 2007, Mays et al., 2010, Mays et al., 2012, Powell et al., 2011 and Wohleb et al., 2011). Indicative of the important role of the SNS in stress-induced immune alteration, these changes are reversed by the blockade of sympathetic signaling prior to stressor exposure (Wohleb et al., 2011).

The stress response in vertebrates stems from internal or external stimuli that trigger the “fight or flight” and "defeat/withdrawal" responses expressed in sympathetic nervous system (SNS) and the hypothalamic–pituitary–adrenal (HPA)-axis activation. Years of research has shown that specific central nervous system (CNS) pathways function as translators of social stimuli into peripheral biological signals that regulate inflammatory responses.

For instance, stress activates neuroendocrine and autonomic pathways like the HPA axis, and the SNS resulting in the release of GC, catecholamines, and pro-inflammatory cytokines such as IL-1, IL-6, and TNF-α. The release of these sympathetic, neuroendocrine, and immune factors has a profound influence on immunity, behavior, and physiology in both humans and rodents and triggers peripheral biological responses that, in turn, signal back to the CNS to complete a bi-directional communication circuit. This is evident in models of repeated social defeat, like SDR, that enhance immune responses to microbial, viral, and allergic challenges and promote and prolong anxiety-like behavior in rodents (Kinsey et al., 2007, Bailey et al., 2009a, Bailey et al., 2009b and Mays et al., 2010). Social disruption stress-induced prolonged anxiety-like behavior coincides with a unique pattern of c-Fos activation in brain regions associated with fear and threat appraisal. For example, repeated social defeat, termed social disruption (SDR) causes increased c-Fos activation in the prefrontal cortex, amygdala, hippocampus, paraventricular nucleus, bed nucleus of the stria terminalis and the lateral septum (Wohleb et al., 2011). [Powell, Tarr, and Sheridan, 2013, p. 3]

When the HPA and SNS circuitry are activated, the release of neurotransmitters and stress hormones generates compensatory physiologic changes that impact behavior and the function of the immune system. In humans, chronic or repeated exposure to stress appears to lead to increases in the expression of inflammatory biomarkers, worsened disease states, and affective/emotional disorders (Glaser and Kiecolt-Glaser, 2005; Gouin et al., 2012).

In several studies, stressed individuals exhibit reduced anti-inflammatory glucocorticoid regulation and increased inflammatory nuclear factor (NF)-κB signaling (Miller et al., 2008). In these situations, psychosocial stress represents a challenge to homeostasis that manifests as physiological alterations in the body (Glaser and Kiecolt-Glaser, 2005).

This may be something to look at in terms of how trauma impacts the brain and body, a microbiological model of traumatic stress, inflammation, and the alteration of adhesion molecules, all of which leads to impaired learning and impaired memory.

As of now, there are no known interventions at the cellular level for altering integrin function. However, the are many ways to control and eliminate inflammation. Among the most well-researched (I could provide citations for these, but it's late, so I might add them later):

1) Curcumin/turmeric
2) Resveratrol
3) Exercise
4) Stress-reduction techniques, such as meditation
5) Avoiding smoking, drinking, and processed foods

We have some control over how our bodies manage and adapt to stress. We are not merely victims of our biology.