M2 microglia and macrophages drive oligodendrocyte differentiation during CNS remyelination

In the paper

“In contrast, M1 ‘classically activated’ phenotypes are associated with enhanced antigen presentation properties and secretion of pro-inflammatory cytokines and reactive oxygen/nitrogen species9.”

What the sources say

• Supported

  The Introduction says classically activated macrophages produce oxygen and nitrogen radicals and secrete inflammatory cytokines. The Results section on antigen presentation reports that they up-regulate MHC Class II and CD86 and induce T-cell activation, supporting enhanced antigen-presenting properties; it also notes that Type II-activated macrophages showed still higher expression. (LLM, conf=0.92)

  cites [9] Edwards, J.P., Zhang, X., Frauwirth, K.A. & Mosser, D.M. Biochemical and functional characterization of three activated macrophage populations. J. Leukoc. Biol. 80, 1298–1307 (2006). source

In the paper

“which secrete anti-inflammatory cytokines/growth factors9.”

What the sources say

• Partly supported

  The Introduction identifies both type II-activated and alternatively activated macrophages as M2 phenotypes, and the Results report that type II-activated macrophages secrete high levels of the anti-inflammatory cytokine IL-10. But the Results also report that alternatively activated macrophages secreted no detectable IL-10 under the tested conditions; the cited passages do not establish growth-factor secretion. The claim therefore overgeneralizes across M2 phenotypes. (LLM, conf=0.88)

  cites [9] Edwards, J.P., Zhang, X., Frauwirth, K.A. & Mosser, D.M. Biochemical and functional characterization of three activated macrophage populations. J. Leukoc. Biol. 80, 1298–1307 (2006). sourceExperimental — accuracy not yet measured

In the paper

“they also exhibit regenerative properties through the phagocytosis of myelin debris3, 4 and secretion of growth/neurotrophic factors5.”

What the sources say

• ?Not checked — no full text of the sourcecites [3] Kotter, M.R., Li, W.W., Zhao, C. & Franklin, R.J.M. Myelin impairs CNS remyelination by inhibiting oligodendrocyte precursor cell differentiation. J. Neurosci. 26, 328–332 (2006). source
• Supported

  This source is cited for myelin-debris phagocytosis, not for growth/neurotrophic-factor secretion, which has a separate citation. The Results section reports that young macrophages enhance remyelination by clearing inhibitory myelin debris; the Discussion likewise identifies their greater debris-clearance capacity as central to this effect. (LLM, conf=0.92)

  cites [4] Ruckh, J.M. et al. Rejuvenation of regeneration in the aging central nervous system. Cell Stem Cell 10, 96–103 (2012). source
• ?Not checked — no full text of the sourcecites [5] Kotter, M.R., Zhao, C., van, R.N. & Franklin, R.J.M. Macrophage-depletion induced impairment of experimental CNS remyelination is associated with a reduced oligodendrocyte progenitor cell response and altered growth factor expression. Neurobiol. Dis. 18, 166–175 (2005). source

In the paper

“Regenerative properties of microglia/macrophages following injury to muscle6, 7 and skin8 are associated with alternative or deactivation to M2-polarized phenotypes (M2a and M2c, respectively), which secrete anti-inflammatory cytokines/growth factors9.”

What the sources say

• Partly supported

  The Discussion (page unavailable) links muscle regeneration to macrophages acquiring an anti-inflammatory M2 phenotype, and the paper reports impaired muscle repair when M2-specific gene expression is disrupted. It does not identify the muscle-associated phenotype specifically as M2a. The skin/M2c portion is attached to a different citation in the citing sentence, so it is not assessed against this source. (LLM, conf=0.85)

  cites [6] Ruffell, D. et al. A CREB-C/EBPbeta cascade induces M2 macrophage–specific gene expression and promotes muscle injury repair. Proc. Natl. Acad. Sci. USA 106, 17475–17480 (2009). sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [7] Dayan, V. et al. Mesenchymal stromal cells mediate a switch to alternatively activated monocytes/macrophages after acute myocardial infarction. Basic Res. Cardiol. 106, 1299–1310 (2011). source
• Partly supported

  For the skin-injury portion cited to this paper, the Results (Comparison of markers of M1 and M2 macrophages; page not provided) report predominantly M2 markers later in cutaneous wound healing. The Discussion links M2 macrophages to tissue repair and angiogenesis, but does not identify the skin-associated phenotype as M2c or establish that a shift to M2 causes regeneration. The muscle-injury citations are separate from this source. (LLM, conf=0.86)

  cites [8] Deonarine, K. et al. Gene expression profiling of cutaneous wound healing. J. Transl. Med. 5, 11 (2007). sourceExperimental — accuracy not yet measured
• Partly supported

  The Introduction (page unavailable) says type II-activated macrophages secrete IL-10, making them anti-inflammatory. That supports the anti-inflammatory cytokine portion of the statement cited to this paper, but the cited passages do not establish secretion of growth factors or that both named M2 phenotypes secrete them. The muscle- and skin-injury portions carry different citations. (LLM, conf=0.84)

  cites [9] Edwards, J.P., Zhang, X., Frauwirth, K.A. & Mosser, D.M. Biochemical and functional characterization of three activated macrophage populations. J. Leukoc. Biol. 80, 1298–1307 (2006). sourceExperimental — accuracy not yet measured

In the paper

“A switch from M1- to M2-associated gene expression has been reported during cutaneous wound healing8 but has not been observed in studies of immune-mediated36 and toxin (cuprizone)-induced demyelination37.”

What the sources say

• Supported

  The Results (‘Comparison of markers of M1 and M2 macrophages’) report that early wound-healing expression included 11 M1 and seven M2 markers, while later expression included nine M2 and one M1 marker. The citation to this paper attaches to the cutaneous wound-healing clause, not the demyelination comparison. (LLM, conf=0.90)

  cites [8] Deonarine, K. et al. Gene expression profiling of cutaneous wound healing. J. Transl. Med. 5, 11 (2007). source
• ?Not checked — no full text of the sourcecites [36] Mikita, J. et al. Altered M1/M2 activation patterns of monocytes in severe relapsing experimental rat model of multiple sclerosis. Amelioration of clinical status by M2 activated monocyte administration. Mult. Scler. 17, 2–15 (2011). source
• Supported

  Citation 37 attaches to the cuprizone-induced demyelination clause, not the separate claims about wound healing or immune-mediated demyelination. In the Discussion (page unavailable), the authors report no evidence for distinct demyelination- and remyelination-associated microglial phenotypes. The Microglia Phenotype section likewise reports that both M1- and M2-associated markers increased during demyelination and remyelination, supporting the absence of an observed M1-to-M2 switch in this model. (LLM, conf=0.93)

  cites [37] Olah, M. et al. Identification of a microglia phenotype supportive of remyelination. Glia 60, 306–321 (2012). source

In the paper

“the receptor which is recruited by ligand-bound Acvr2 and which is required for subsequent functional downstream signalling33.”

What the sources say

• Partly supported

  The Abstract says ligand-bound ActR-IIB associates with ActR-IB, and that ActR-IB acts as a downstream transducer whose GS-domain mutations abrogate signal propagation. This supports the recruitment and signalling mechanism, but the studied type II receptor is ActR-IIB, not the specifically named Acvr2. (LLM, conf=0.84)

  cites [33] Attisano, L., Wrana, J.L., Montalvo, E. & Massague, J. Activation of signaling by the activin receptor complex. Mol. Cell Biol. 16, 1066–1073 (1996). sourceExperimental — accuracy not yet measured

In the paper

“Additionally, TGFβ isoforms have been shown to induce myelin protein expression42, 43.”

What the sources say

• ?Not checked — no full text of the sourcecites [42] Diemel, L.T., Jackson, S.J. & Cuzner, M.L. Role for TGF-beta1, FGF-2 and PDGF-AA in a myelination of CNS aggregate cultures enriched with macrophages. J. Neurosci. Res. 74, 858–867 (2003). source
• Partly supported

  The Results report that recombinant TGF-β1 increased the proportion of cultured O-2A cells expressing galactocerebroside, a marker of oligodendrocyte differentiation (Fig. 8). Galactocerebroside is not a protein, and the passages do not show that TGF-β isoforms induce myelin protein expression. The isoform-expression Results (p. 1399) identify TGF-β2 and TGF-β3 in oligodendrocytes but do not test their effect on myelin proteins. (LLM, conf=0.87)

  cites [43] McKinnon, R.D., Piras, G., Ida, J.A. Jr. & Dubois-Dalcq, M. A role for TGF-beta in oligodendrocyte differentiation. J. Cell Biol. 121, 1397–1407 (1993). sourceExperimental — accuracy not yet measured

In the paper

“A custom qPCR array plate (SABiosciences) was designed to include primers for M1 and M2-associated genes that were detected as being significantly upregulated in a microarray screen of a remyelinating lesion of the rat caudal cerebellar peduncles in vivo18.”

What the sources say

• Partly supported

  The Results section, “Increased Rxrg transcripts in CNS remyelinating lesions” (page unavailable), reports a microarray screen of rat caudal cerebellar peduncle lesions and identifies significantly differentially expressed genes, including inflammation-associated genes expressed more highly at 5 days post-lesion. Our copy does not identify those genes as M1- or M2-associated or establish that the genes selected for the citing paper’s qPCR plate were significantly upregulated. (LLM, conf=0.84)

  cites [18] Huang, J.K. et al. Retinoid X receptor gamma signaling accelerates CNS remyelination. Nat. Neurosci. 14, 45–53 (2011). sourceExperimental — accuracy not yet measured

In the paper

“In accordance with our finding, signalling pathways downstream of activin receptor activation include Rac/Cdc42 GTPases, Akt, and mammalian target of rapamycin (mTOR), all of which have been previously implicated in positively regulating oligodendrocyte differentiation and/or myelination38-41.”

What the sources say

• Supported

  The Results section (‘Rho family GTPases regulate OPC morphologic differentiation’) reports that dominant-negative Cdc42 or Rac1 inhibited oligodendrocyte morphologic differentiation. The Discussion reports that activated Rac and Cdc42 promoted more highly differentiated cells. This supports the Rac/Cdc42 portion for which this paper is cited in the multi-citation sentence; the activin-receptor framing is the citing authors’ own finding. (LLM, conf=0.90)

  cites [38] Liang, X., Draghi, N.A. & Resh, M.D. Signaling from integrins to Fyn to Rho family GTPases regulates morphologic differentiation of oligodendrocytes. J. Neurosci. 24, 7140–7149 (2004). source
• Supported

  The Introduction and the section ‘Rac1 is required for proper axon ensheathment and myelination’ identify Cdc42 and Rac1 as important for CNS myelination. This supports the part of the multi-citation sentence for which this paper is offered: that Rac/Cdc42 signaling has been implicated in myelination. (LLM, conf=0.90)

  cites [39] Thurnherr, T. et al. Cdc42 and Rac1 signaling are both required for and act synergistically in the correct formation of myelin sheaths in the CNS. J. Neurosci. 26, 10110–10119 (2006). source
• Supported

  For the Akt component of this multi-citation sentence, the Introduction reports that constitutively active Akt enhanced oligodendrocyte maturation and increased CNS myelin production in transgenic mice. The copy does not provide a page number. (LLM, conf=0.92)

  cites [40] Flores, A.I. et al. Constitutively active Akt induces enhanced myelination in the CNS. J. Neurosci. 28, 7174–7183 (2008). source
• Partly supported

  The Discussion (page not supplied) reports that mTOR signaling is required for a late stage of oligodendrocyte differentiation and the onset of myelination, and discusses enhanced myelination with an overactive PI3K/Akt/mTOR pathway. It does not establish that Rac/Cdc42 positively regulate these processes or that the listed pathways act downstream of activin receptor activation. (LLM, conf=0.87)

  cites [41] Guardiola-Diaz, H.M., Ishii, A. & Bansal, R. Erk1/2 MAPK and mTOR signaling sequentially regulates progression through distinct stages of oligodendrocyte differentiation. Glia 60, 476–486 (2012). sourceExperimental — accuracy not yet measured

In the paper

“The rapid depolarization of microglia in the absence of polarizing factors (data not shown) required these to be present during conditioning of media”

In the paper

“GFP+ iNOS+ CD68+ M1 macrophages and GFP+ Arg-1+ CD68+ M2 macrophages present within the lesion (Fig. 6f) only contributed to 3.6 ± 1.6 % of iNOS+ M1 cells and 12.4 ± 5 % of Arg-1+ M2 cells.”

In the paper

“Assessment of activin-A binding capacity of other cell types within lesions indicates that Acvr2 is expressed by CC1+ oligodendrocytes (Acvr2B+) and CD68+ microglia/macrophages (Acvr2A+, Acvr2B+), but not by GFAP+ astrocytes or NF+ axons (Supplementary Fig. 9 online).”

In the paper

“Contaminating astrocytes were < 7% of the culture in all polarization states (data not shown).”

In the paper

“All manual cell counts were performed in a blinded manner.”

In the paper

“Each condition was performed in quadruplicate wells and the experiment was repeated with 3 independent OPC samples and 3 conditioned media samples.”

In the paper

“Diagnosis of MS was confirmed by neuropathological means by Dr F. Roncaroli (Consultant Neuropathologist, Imperial College London) and clinical history was provided by Dr R. Nicholas (Consultant Neurologist, Imperial College London)”

In the paper

“3-5 independent supernatant sets were used.”

In the paper

“successful polarization under these growth conditions was confirmed (data not shown).”

In the paper

“No statistical methods were used to predetermine sample sizes but these were similar to those generally employed in the field.”

In the paper

“All assays represent a minimum of 3 independent experiments treated with conditioned media from at least 3 microglial preparations.”

In the paper

“whereas glatiramer acetate induces a peripheral M2 phenotype48”

What the sources say

• ?Not checked — no full text of the sourcecites [48] Weber, M.S. et al. Type II monocytes modulate T cell–mediated central nervous system autoimmune disease. Nat. Med. 13, 935–943 (2007). source

In the paper

“the CNS-permeable therapy FTY720 decreases peripheral M1 and M2 polarization in rodents47”

What the sources say

• ?Not checked — no full text of the sourcecites [47] Schaier, M. et al. Role of FTY720 on M1 and M2 macrophages, lymphocytes, and chemokines in 5/6 nephrectomized rats. Am. J. Physiol. Renal Physiol. 297, F769–F780 (2009). source

In the paper

“Antibody isotype controls (Sigma) added to sections at the same final concentration as the respective primary antibodies showed little or no non-specific staining.”