Discussion
Explain to someone who doesn't understanding: When you get injured, your body sends special cells, macrophages, to clean up the damage and repair the area. These cells call for other cells called, fibroblasts, which build a scaffolding, called the ECM, that helps rebuild the injury. The scientists in this paper are looking for if different types of macrophages instruct the fibroblasts to build the ECM differently.
t remains unclear how other macrophage phenotypes outside of the traditional M1/M2 paradigm fit into this progression
this is still a gap. yes M1/M2 hybrids exists, but what do those macrophages look like and how are they actually involve in ECM assembly?
e findings are important for understanding and leveraging the functional outcomes of hybrid M1/M2 macrophages in vitro and in vivo and have implications for biomaterial design to promote enhanced tissue remodeling and function.
I would like to see them actually test whether changing the ECM to be more easily remodeled would actually improve the body's response to implants. Yes, this shows that the M1/M2 hybrids are involved, but how will that actually look when an implant come to play?
ith less aligned ECM and increased sulfated glycosaminoglycan
this was a strong experiment to add because you can visually see the decreased alignment and increased thickness in the IL4+IL13 group, which puts into context their PCA data.
llagen V plays key roles in regulating the initial fibrillogenesis of collagen I, and its assembly with collagen I suggests a role in reducing alignment,
reduces fibril alignment
Therefore, hybrid M1/M2 phenotypes are likely a normal part of healthy wound healing
This is the hypothesis: hybrid M1/M2 phenotypes play a role in normal wounding healing and the development of fibrosis during the foreign body response.
I think they did not do a good job of stating it, and may have strayed from this point by the end of the paper
While gene expression analysis is useful for assessing molecular mechanisms, the data represent a snapshot in time, whereas structural changes develop and persist over longer time scales. Therefore, histological and biochemical analyses
I like that they included another test that wasn't just a PCA to support their results and looked into the structural biology
increased expression of the M2 markers Arg1, Cd163, Chil3, and Igf1 compared to the blank control group at day 3 (Fig. 4C), while expression of M1 genes was generally unaffected by release of IL4+IL13, except for Tnf
so as macrophages were changing from M1 to M2, the M1 genes were still present
ene expression analysis of the surrounding cells showed dose-dependent increases in several genes involved in ECM assembly
when you increase the factors that promote the M2 phenotype, there is an increase in ECM assembly genes
er diameter compared to the control and M0 groups, while M1/M2-conditioned media caused an increase in fiber diameter
I wish they explained the relevance of reduced vs increased fiber diameter
M2 macrophages also induced fibroblasts to express the highest levels of genes involved in angiogenesis, including the genes encoding PDGFA, VEGFA, DACT1, and the tyrosine kinase protein FYN, with significant differences compared to the control (Fig. 2B). However, it is important to note that there were no significant differences between fibroblasts
i feel like these contradict each other a bit. So the macrophages themselves induced fibroblasts, but when treated with macrophage signals, there is no change to fibroblasts?
M2, M1/M2, and M1→M2
seems like the M2 adjacent macrophages are the ones that are most involved in fibrosis from initial conclusions
a major growth factor involved at later stages of angiogenesis and which also plays a role in fibrosis
this seems as though it might not be as conclusive whether it plays a role in fibrosis
o M1 or M2 phenotypes, and two unique hybrid phenotypes: M1/M2, which was generated through the simultaneous addition of both M1- and M2-promoting stimuli, and M1→M2
I like that they included all of the different phenotype variations. Include M1--> M2 was smart since that appears to be what normally occurs in the body
the role of macrophage phenotype in ECM assembly and fibrosis in vitro and in vivo
Macrophage reactions to biomaterial implants can cause fibrosis, which can affect the effectiveness of the implant. The authors want to find out the mechanisms behind this reaction, so they are looking at hybrid macrophage phenotypes, which is an understudied area of research.
the role of hybrid macrophage phenotypes in biomaterial-mediated fibrosis is still unknown.
gap in the field that they are looking to explore
o hallmarks of fibrosis
cytokines promoted by both M1 and M2 are associated with the development of fibrosis
mediated by M2-type macrophages [
makes sense since M2-type macrophages are associated with healing resolution
ybrid M1/M2 phenotype b
M1 macrophages -> proinflammatory M2 macrophages -> pro healing resolution M1/M2 macrophages -> phase in between healing initiation and resolution
Macrophages are essential to the wound healing process and possess the ability to modulate fibroblast activities
macrophages affect fibroblast activity, which can lead to the development of fibrosis in an injury or implantation
xcessive collagen deposition, increased matrix stiffness, and highly aligned ECM
characteristic results of a foreign body response
The foreign body response, a form of biomaterial-mediated fibrosis in which biomaterials become encapsulated within fibrous tissue and isolated from the rest of the body, impedes the function of many biomaterial implants.
set back of using implants, as stated in the abstract
specially in M2-conditioned media
relevance of M2 to ECM assembly
pro-inflammatory M1, prohealing M2, and a hybrid M1/M2
important definitions of M1, and M2
the progression of the foreign body response is poorly understood
gap in research they will potentially explore
implants become encapsulated in thick fibrous tissue that prevents their proper function
introducing the problem