Review for 10.1186/s12876-020-01515-5 (2020)

Reviewer’s report
Title: 
HFD and HFD-provoked Hepatic Hypoxia act as Reciprocal Causation for
NAFLD via HIF-independent Signaling
Version: 
0 
Date: 
13 Jul 2020
Reviewer's report:
Zhang et al. in this manuscript provide evidence that hypoxia and lipid
accumulation form vicious cycle to promote NAFLD disease conditions in HIFs-
independent manner. 
The manuscript addresses some interesting points but appears incomplete and
inadequate at the specific important observations. 
Major criticisms;
1.The authors treated newborn mice with 75 % oxygen for 5 days followed by 21
% oxygen for another 5 days, and designated as "hypoxia treatment". Although
pimonidazole-adducts were detected in the mouse liver (Figure 4A), the reviewer
thinks that this treatment mimics hyperoxia followed by normoxia, and these
alterations do not occur in NAFLD patients. The authors should explain the
reason why you did not treat mice with 7~10 % oxygen to evoke hypoxia in
vivo, and check if the low oxygenated conditions could stimulate lipid
infiltration with altered gene expressions of lipid metabolism in mouse liver as
well. On the other hand, the authors also mentioned that intermittent, but not
chronic, hypoxia is a hallmark of OSAS, that is tightly linked with NAFLD. The
reviewer requests the authors to explain the reason why you did not reproduce
the same conditions in obese adult mice. 
2.The authors clearly showed lipid infiltration in mouse liver exposed to either
HFD (Figure 1D) or hypoxia (Figure 4B). However, there is no description about
the region (periportal, pericentral or homogenously) of lipid accumulation and
hypoxia in liver acinus. In addition, the authors should examine whether lipid
accumulation and hypoxia occur in the same region among liver acinus in each
experimental condition.
3.In mice, hypoxia increases and decreases gene expression involved in
lipogenesis and lipolysis, respectively (Figure 4D and 4E). Can hypoxia elicit the
similar changes in vitro? Based on your hypothesis, hypoxia and lipid
accumulation enhances its effects reciprocally. If so, can simultaneous exposure
to hypoxia and palmitate further deteriorate lipid accumulation? In addition, the
reviewer wonders if exposure of mice to HFD evokes the similar alterations in
the gene expressions to those in hypoxia-treated mice.
Minor criticisms;
1.There is no information about sequences of siRNAs against HIF-1alpha and -
2alpha, with transfection methods.
2.The authors should describe experimental conditions in detail. For example,
information about cell density, age and sex of mice, and timing of liver sampling
(fed or fasted conditions) is lacking.
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No
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authors.
Yes
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Yes
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Needs some language corrections before being published
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