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Chronic inflammation is a
hallmark of impaired healing in a plethora of tissues, including skin, and is
associated with aging and diseases such as diabetes. Diabetic chronic skin
wounds are characterized by excessive myeloid cells that display an aberrant
phenotype, partially mediated by stable intrinsic changes induced during
hematopoietic development. However, the relative contribution of myeloid
cell–intrinsic factors to chronic inflammation versus aberrant signals from
the local environmental was unknown. Moreover, identification of myeloid cell
intrinsic factors that contribute to chronic inflammation in diabetic wounds
remained elusive. Here we show that Gr-1+CD11b+ myeloid cells are retained
specifically within the presumptive granulation tissue region of the wound at
a higher density in diabetic mice and associate with endothelial cells at the
site of injury with a higher frequency than in nondiabetic mice. Adoptive
transfer of myeloid cells demonstrated that aberrant wound retention is due to
myeloid cell intrinsic factors and not the local environment. RNA sequencing
of bone marrow and wound-derived myeloid cells identified Selplg as a myeloid
cell intrinsic factor that is deregulated in chronic wounds. In vivo blockade
of this protein significantly accelerated wound healing in diabetic mice and
may be a potential therapeutic target in chronic wounds and other chronic
inflammatory diseases.
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ملخص المشاركة:
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Cutaneous wound healing requires
recruitment and differentiation of innate immune cells, particularly
macrophages, from bone marrow cells for efficient tissue repair and
regeneration. Patients with diabetes suffer from impaired wound healing that
can lead to lower limb amputation. Prolonged chronic inflammation in both
diabetic mouse models and human patients is associated with dysfunctional
macrophages that fail to transit from pro-inflammatory phenotype (M1-like) to
a pro-healing phenotype (M2-like). It has been demonstrated that diabetic
environment induces aberrant macrophage phenotype that is partially mediated
by stable intrinsic changes, but the underlying mechanisms have not yet been
elucidated.
In this study, we have used bone
marrow derived-macrophages isolated from diabetic and non-diabetic mice and
either non activated (NA) or classically activated (CA) by LPS and INF-γ
(M1-like) or Tnf activated (M1-like) to identify any changes in
pro-inflammatory genes due to the diabetic environment. Crucially, we show
that diabetes increases expression of many of the pro-inflammatory genes such
as Tnf, Ccl2, and Nos2. Moreover, we have investigated deregulation in the
expression of key M1/pro-inflammatory macrophage transcription factor NF-kB
P65 and its natural inhibitor IKBα, both at the RNA and the protein level.
Interestingly, this was also associated with misexpression of
chromatin-remodelling enzymes, including Histone acetyltransferases (HATs)
and Histone deacetylases (HDACs), which are important in regulating the
transcription factor activity and histone modifications to facilitate gene
transcription.
Our data suggest a possible link
between chronic inflammation and elevated M1 polarization in diabetic wounds
due to deregulation of NF-kB activity and histone acetylation enzymes.
In addition, we have used
protein transduction of Hoxa3, a factor that is normally upregulated in
wounds, but is repressed in diabetic wounds, to modulate the aberrant
diabetic macrophage phenotype in vitro. Importantly, here we show that Hoxa3
induces macrophage maturation and inhibits the pro-inflammatory
hyperpolarization, possibly by regulation of NF-kB, a critical regulator of
inflammation, and its cofactor of HAT enzymes. Altogether our data suggest a
potential for Hoxa3 protein transduction as a therapeutic.
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