miR-155 Expression in Episodic and Chronic Migraine

Background:

Depending on the median frequency of headache, migraine is defined as episodic migraine (EM) (for those who have less than 15 migraine days per month), or chronic migraine (for those who have at least 15 headache days per month, 8 of which with migraine features, for at least three months). The chronification of migraine is often associated with a progressive increase of acute medications intake, leading to a condition known as Medication Overuse Headache (CM-MOH).

So far, there are no validated and reliable biomarkers of migraine, but the headache scientific community is intensely investigating the neurobiological signatures of migraine. Validated biological biomarkers may allow several steps forward in the management of migraine by: (I) refining the diagnosis according to biological features; (II) predicting the response to advanced therapies; (III) predicting which patients are at the greatest risk of migraine chronification and mark different phases of the migraine cycle; (IV) the identification of novel molecular targets for drugs development. Fulfilling these purposes, a class of molecules that has recently gained enormous interest are microRNAs (miRNAs). miRNAs are small endogenous noncoding RNAs that are around 22 nucleotides in length. miRNAs operate as post-transcriptional regulator of gene expression by promoting messenger RNA (mRNA) degradation or repressing mRNA translation. The regulation process performed by miRNAs is complex and articulated since an individual miRNA might target hundreds of different mRNAs, and conversely, each mRNA may be regulated by multiple miRNAs. It has been estimated that more than 60% of all protein-coding genes are regulated by miRNAs which consequentially determine the pleiotropic modulation of a wide variety of cellular processes involving differentiation, development and signaling. miRNAs are involved in the generation and maintenance of pain and several evidence suggest that specific miRNAs could play a role in migraine.

The micro-MIG study corroborated the hypothesis that different miRNAs expression is altered in EM and CM when compared to a control group, although no specific miRNAs were identified as a strong and specific migraine molecular signature.

miRNA-155 can be considered as a master regulator of inflammation since its expression can modulate many inflammatory stimuli such as: interleukin 1β (IL-1β), tumor necrosis factor alpha (TNF-α), alarmins (eg, IL-1α), hypoxia, nuclear factor erythroid 2-related factor 2 (NRF2), pathogen-associated and damage-associated molecular patterns as well as to toll-like receptor ligand (TLR) in various cell types. Recently, several lines of preclinical evidence further highlighted the role of miRNA-155 in inflammation and pain generation and maintenance also as a feasible therapeutic target. The inhibition of miRNA-155 can alleviate hyperalgesia and bone cancer pain as well as neuropathic pain in in-vivo rodent models. Therefore, it can be inferred that miRNA-155 might also play an important role in neurogenic inflammation, a process supposed to take place in the trigeminovascular system, and related to the pathogenic mechanisms underlying migraine pain.

Monocytes are immune system components which may play a role in migraine. For example, abortive migraine treatment may influence monocyte function. Acetylsalicylic acid inhibits monocyte chemotaxis, whereas metoprolol, metoclopramide, dihydroergotamine, and sumatriptan have no impact. microRNAs have been shown to regulate macrophage polarization and subsequent effects on inflammation.

Aims:

In order to shed light upon the mediators involved in migraine pathophysiology and its chronification, we aim to asses the different expression of miRNA-155 (in monocytes) in patients with EM, CM-MOH and healthy controls (HCs). Secondly, we aim to provide information about distribution of monocyte phenotype in the three groups.

Expected evaluations:

For all patients is scheduled a single evaluation over time - baseline (T0) - in the interictal migraine phase, during which they will undergo:

• informed consent signing
• screening visit
• clinical and demographic data collection (based on revision of a headache diary)
• venous blood sampling All patients will be evaluated in the morning, after night fasting, and in the inter-ictal migraine phase.

Detailed description of the methods planned for the biochemical analyses could be found here:

• 10.1186/s10194-020-01189-0;
• 10.1177/0333102420949201.

Sample size calculation:

Sample size was calculated from preliminary data available, which showed a difference in miR-155 levels in peripheral mononuclear cells of 1.69 RQ (relative quantification), with standard deviations of 1.15, and 2.69 RQ in healthy control and episodic migraine subjects, respectively. This difference has been assumed the same between episodic and chronic subjects.

Therefore, assuming a statistical power of 80 percent, a significance level of 95 percent and performing Bonferroni correction, we need a sample size of 24 subjects for the three experimental groups (HCs, CM-MOH and EM). Considering possible variability in dosing, we will enroll at least 30 subjects per group.

Pre-planned statistical analysis:

The difference between of miR155 expression among CM-MOH, EM and HCs will be determined by parametric (ANOVA) or non-parametric (Kruskal-Wallis) tests depending on the distribution of data. Parametric or non-parametric correlations will be used to measure the relationship between biochemical variables and clinical variables in CM-MOH and EM patients. Multivariate analyses will be performed according to the results of the univariate analysis. Statistical significance will be set at the 5% level (p<0.05).