Summary: The central idea behind the experiment for this paper was that mosaic expression of
BRAF(V600E) in mouse EMPs causes clonal expansion of macrophages and thus delays the
progression of neurodegenerative disorders. The experiments shown in Figure 1 were done by
inducible gene targeting, introducing YFP into the macrophage lineage. Counts were taken of the
YFP protein in a variety of cell types, and was detected in F4/80 tissue macrophages. Further
experiments were done on the macrophages expressing YFP, namely RNA sequence analysis.
The results of the sequence analysis indicated expression of BRAF(V600E) in pulse labeled mice
as well as showed an increase of F4/80 YFP macrophages in tissues. Further RNA sequence
analysis demonstrated expression of ERK target genes as well as cytokines. Flow cytometry
analysis conducted after showed no blatant issues with tumoural or leukemic phenotypes.
Further experiments were conducted to analyze the effects of macrophage clones with
BRAF(V600E) in adult tissues through longitudinal analysis of a vast cohort of BRAF mice,
which were shown to slowly develop neurological impairment. Figure 2 in this paper describes a
variety of methods used by the researchers, such as footprint assays and controlled diet
experiments. These experiments showed that a large majority of male and female BRAF/VE
mice with neurological disease by 7 months progressed to complete paralysis by 9 months. The
cumulative incidence rate of behavioral abnormalities continued to increase as time went on,
showing that as time passes, symptoms continue to develop. Immunostaining for certain proteins
(such as CD68 and YFP) showed that microglial clusters led to an increase of ERK microglia.
ERK activation was also confirmed in the brain and spinal cord area, as well as demonstrating
that the presence of B cells, monocytes, and granulocytes was not abundant while T cell
expression was increased. These results evidence the researchers claim that mosaicism in
microglia drives neurodegenerative diseases. Gene enrichment analysis was also used to show
that ERK activation resulted in the proliferation of inflammatory cytokines, which are signals of
neurodegeneration.
Critique: This was a very dense paper with many results that proved to be significant in the field
of neurodegenerative disease. Some questions I have about the mutation in general, however, are
how does this disease start initially? What molecular machinery can trigger the somatic
mutation? Are these mutations strictly molecular or can environmental factors also impact the
disease, such as sunlight or UV radiation. Furthermore, from the perspective of a
healer/researcher interested in the solution to neurodegenerative diseases, is there a way to
prevent expansion of ERK microglia despite having the BRF V600E allele present in the
organism. Furthermore, from personal experience, the technique of pulse labeling which was
used to target EMPs is prone to a lot of experimental error due to the fact that degradation of the
labeled material can present inaccurate results of values.