Glucose Stimulates Glial Cell Line-Derived Neurotrophic Factor Gene Expression in Microglia through a GLUT5-Independent Mechanism

Round 1

Reviewer 1 Report

The work presented here regards the effect of glucose on hypothalamic Gdnf and Manf mRNA expression in mice as well as mRNA and protein levels in murine microglial cell line SIM-A9. The approach used is based on intra-cerebroventricular or intra-peritoneal glucose treatment and exposure of the microglial cell line SIM-A9 to high glucose concentrations. The latter experiments are performed in the presence or absence of GLUT5 inhibitor treatment. The data indicate that high glucose increases Gdnf mRNA and proteins in microglia. However the increase is not blocked in the presence of the GLUT5 inhibitor. The regulation of Manf is more complex. The work is clearly written except the few points listed below :

1.      Besides, Gdnf, the introduction (Line 43) and the beginning of the results (line 92) mention MANF, another neurotrophic factor, which is involved in hyper/hypo-phagia in hypothalamus. Unlike Gdnf, Manf is not regulated by glucose treatment in the hypothalamus in contrast to data previously reported by others. The authors comment this discrepancy in the discussion. Manf data should be included in the abstract.

2.      As suggested in the Discussion, the identification of Gdnf and Manf-expressing cells in the hypothalamus would resolve cell-type specific response to glucose and of course, would substantially improve the data presented in Figure 1. The visualization of Gdnf / Manf expressiong cells by in situ hybridization and/or immunostaining might also contribute to explain the discrepancy mentioned above since Manf expression has been proposed to be detected in several cell types.

3.      Figure 1 legend is not consistent with what is shown in the panels. Indeed, A,B and C,D are not i.p. and i.c.v., respectively.

4.      In Figure 3, why only glucose-induced GDNF protein expression has been determined in SIM-A9 and not MANF protein ?

5.      Lines 231-234 : The last sentence is difficult to understand since SIM-A9 are not derived from hypothalamus but cerebral cortex (line 107).

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Points to be discussed in the manuscript:

- it would be interesting to learn already in the Results section why the authors decided to use certain specific concentrations of glucose in their experiments. This point is discussed later and the comparison with concentrations in vivo, in certain brain regions are certainly a very interesting point

- the authors mention that “it remains to be shown whether glucose influences microglial Gdnf and Manf gene expression in specific brain regions”. However, it would be also interesting to know the differences in local glucose concentrations in different brain regions.

Minor points:

- the statistical significance should be depicted directly in the graph, e.g. Figure 1B

- the authors should explain why only one concentration of fructose was tested

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Suitable answers have been provided.