Preprint The alpha-2A-adrenergic receptor (ADRA2A) modulates susceptibility to Raynaud's syndrome 2023 Tervi et al

[Andy]

Abstract

Raynaud's syndrome is a common dysautonomia where exposure to cold increases the vascular tone of distal arteries causing vasoconstriction and hypoxia particularly in the extremities. Current treatment options are limited and unspecific. Biological mechanisms leading to the phenotype remain uncharacterized. Using genetic and electronic health record data from the UK Biobank, the Mass-General Brigham Biobank, the Estonian Biobank, and the FinnGen study, we identified 11,605 individuals with a diagnosis for Raynaud's syndrome and 1,116,172 population controls.

We found eight loci including endothelial nitric oxide synthase (NOS3), HLA, and a notable association at the alpha-2A-adrenergic receptor (ADRA2A) locus (rs7090046, P = 3.93x10-47), implicating adrenergic signaling as a major risk factor with Raynaud's syndrome. We further investigate the role of the variants and ADRA2A expression in functional and physiological models. In silico follow-up analysis revealed an expression quantitative trait locus (eQTL) that co-localized and increased ADRA2A gene expression in tissue specific manner in the distal arteries. Staining with RNA scope further clarified the specificity of ADRA2A expression in small vessels. We show by CRISPR gene editing that the SNP region modifies ADRA2A gene expression in pulmonary artery smooth muscle cells. Finally, we performed a functional contraction assay on smooth muscle cells in cold conditions and showed lower contraction in ADRA2A-deficient and higher contraction in ADRA2A-overexpressing smooth muscle cells.

Our results indicate that Raynaud's syndrome is related to vascular function mediated by adrenergic signaling through ADRA2A. Our study highlights the power of genome-wide association testing as a discovery tool for poorly understood clinical endpoints and further clarifies the role of adrenergic signaling in Raynaud's syndrome by fine-mapping, using in vitro genomic manipulations and functional validation in distal smooth muscle cell populations located in arterioles.

https://www.medrxiv.org/content/10.1101/2023.10.04.23296526v1

 

[Hutan]

It's quite a collaboration - data from Finland, UK Biobank, Estonian Biobank, Mass General Brigham Biobank. Data from over 1 million people including 11,605 people with RS. Terrific to see that happening.

Consequently, RS can manifest as a comorbidity of diseases with substantial clinical significance, such as systemic sclerosis, lupus erythematosus, myalgic encephalomyelitis/chronic fatigue syndrome and most recently Long COVID.

This is progress.

I think Raynaud's is quite common in people with ME/CFS? I wonder if having that tendency makes it easier to get ME/CFS? I think Systrom is part of Brigham Hospital, so he might be particularly aware of this research, which seems relevant to his work on oxygen extraction in capillaries.

Majority of RS patients are females (73%).

One of the genetic variants found to be associated with RS is associated with peripheral vascular disease (part of the HLA region), and another impacts on endothelial nitric oxide (NOS3). Also ACVR2A (activin receptor type 2A); one near IRX1; one near RAB6C; TMEM51 - a transmembrane protein; one near PCDH10.

The researchers particularly liked the ADRA2A variant, as it stood out as a significant association in each of the tested cohorts and so the rest of the paper is about the investigations they did of the significance of this variant.

ADRA2A encodes for the α2A-adrenergic receptor, is targeted by α-blockers, and has a downstream effect on lowering vascular tone and consequently blood pressure23-28.

 

[Hutan]

Of course, I have no idea, but the picture does look exciting.

 

[EndME]

A couple of months ago I read this news article https://www.news-medical.net/news/2...ns-behind-Raynauds-phenomenon-discovered.aspx. I suppose there would naturally be a significant overlap in the findings since there are overlaps in the biobanks. The news article also states that the paper was published in Nature Communications, but I was never able to find that, I only found this preprint https://www.medrxiv.org/content/10.1101/2022.10.19.22281276v2 (which focuses on IRX1 and ADRA2A). I didn't see an overlap on the authors listed so it seems these two groups were working on the same thing at the same time (most probably knowingly or via some form of collaboration).

 

[Hutan]

The researchers found a number of risk variants for ADRA2A. They suggest that the lead variant affects tibial arteries most, also prostate, brain, small intestine (See. Fig 2 b). They also say that it is expressed primarily in microvasculature.

The team applied their tools to work out specifically which cells in the vascular wall of a blood vessel express ADRA2A. They report that the ADRA2A cells are a relatively small proportion of all the cells.

This cluster expressing ADRA2A is distinct from the medial smooth muscle cells (SMCs) that are the majority of the MYH11+, a classical marker for medial smooth muscle cells that are found in the vessel wall (Figure 3B & 3D). Moreover, the cluster expressing ADRA2A contains cells that express mature SMC genes, and in addition co-express NOTCH3 (Figure 3B & 3C)31,32. These findings suggest that only microvascular cells express ADRA2A and are likely a causal cell population for RS.

It wasn't really clear to me how they knew that cells that express mature SMC genes and NOTCH3 must be microvascular cells. From Fig 3, they seem to have concluded that the cells involved are adventitial pericytes and some SMCs. I'm assuming that's due to pre-existing knowledge in the cell atlas.

And they say that they only found one cell line expressing ADRA2A "that was likely obtained from the pulmonary microvasculature". That sounded a bit vague. They went on to use this cell line in subsequent experiments.

Fig 3A-D



Fig 3G is levels of ADRA2A and NOTCH3 - smooth muscle cells of healthy controls on the left i.e. levels are set as the baseline, so 0. The fold changes (in pink) is very dramatic. (I'm not entirely sure what cells they were working with here.)

 

[Hutan]

They next looked at the impact on the cells that were made to over-express ADRA2A - they concluded they were contracting more.

There's a picture of the theory, but, as far as I can work out, it's pretty simple. People with Raynaud's have more alpha 2a adrenergic receptors on the particular vascular cells. So, when there is cold or another stressor, the adrenergic receptor ligands (epinephrine, norepiphrine) have more sites to attach, and the contraction response is bigger.

They note that previous work in Raynaud's had focused on ADRA2C, but their study found that over expression of that gene didn't produce the cold-related contraction.

Interestingly, a recent preliminary descriptive biobank study has identified some of the same RS loci 42.

@EndME, I think that reference 42 is the paper you mentioned, still in preprint according to the reference list.

In healthy patients without RS, there are mechanisms to prevent unwanted and excessive vessel contraction. First, the cell constriction (upon cold or stress) can be limited by the increased release of ligand by translocation of the α2C-adrenergic receptor from the cytosol to the cell surface. Second, α2A-adrenergic receptors are also expressed on the presynaptic membrane and function there as a negative feedback loop for catecholamine release43.

For example, the signal from chromosome 6, HLA class I region, points towards the possible immune, infectious or autoimmune mechanisms in RS. It is still unclear, however, if this signal is a signal from autoimmune diseases that have secondary RS and not primary Raynaud’s disease per se47,48, which was also indicated by Hartmann et al. (2023) in the UKB

Finally, data from subcutaneous microvascular cells or microvascular cells from RS patients were not available for this study and any genetic or expression effects might be accentuated or changed after disease onset in RS patients.

I haven't read the methods, which comes after the Discussion, but I think I'll just leave it at that for the moment, and feel happy that maybe this paper is progress.

 

[Dolphin]

One of the authors wrote this thread on X:

https://twitter.com/user/status/1710394414215090610

 

[Hutan]

I finally joined twitter today, just to like that tweet. I'm so impressed that this team wanted to understand Long Covid, ME/CFS and POTS and so undertook this large collaboration to look into Raynaud's. And the work was possible because of all the people who have worked on building biodata infrastructure.

This is the stuff that gives me hope. People who drill down into individual symptoms rather than not getting past 'fatigue'. (And, still I haven't read the methods section, and perhaps this study won't end up being part of the answer. But - there are people caring enough to try to answer useful questions and the tools are increasingly there to allow them to do that.)

 

[Trish]

I finally joined twitter today, just to like that tweet

Just as many of us are leaving Twitter!

 

[SNT Gatchaman]

Replicated in ADRA2A and IRX1 are putative risk genes for Raynaud’s phenomenon (2023, Nature Communications)