Running title: Oleic and palmitic acid effects on hypothalamic neurons
Concentration-dependent change in hypothalamic neuronal transcriptome by the dietary
fatty acids: oleic and palmitic acids
Fabiola Pacheco Valencia
1
^, Amanda F. Marino
1
^, Christos Noutsos
1
, Kinning Poon
1
*
1
Department of Biological Sciences, SUNY Old Westbury, Old Westbury NY, United States
^Authors contributed equally to this work
*Corresponding Author:
Kinning Poon
223 Store Hill Rd
Old Westbury, NY 11568, USA
1-516-876-2735
poonk@oldwestbury.edu
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Abstract
Prenatal high-fat diet exposure increases hypothalamic neurogenesis events in embryos and
programs offspring to be obesity-prone. The molecular mechanism involved in these dietary
effects of neurogenesis are unknown. This study investigated the effects of oleic and palmitic acids,
which are abundant in a high-fat diet, on the hypothalamic neuronal transcriptome and how these
changes impact neurogenesis events. The results show differential effects of low and high
concentrations of oleic or palmitic acid treatment on differential gene transcription. Gene ontology
analysis uncovered significant gene enrichment in several cellular pathways involved in gene
regulation and protein production, particularly with proliferation, migration, and cell survival. The
enriched signaling pathways include Wnt, integrin, PDGF, and apoptosis, in addition endocrine
function signaling pathways CCKR and GnRH. Further examination of proliferation and migration
show low concentrations of oleic acid to stimulate proliferation and high concentrations of both
oleic and palmitic acid to stimulate apoptosis. Oleic acid also reduced hypothalamic neuronal
migration, with little effects by palmitic acid. The results show direct impact of the two most
abundant fatty acids in a high fat diet to directly impact hypothalamic neuronal proliferation and
migration. The results also uncovered signaling pathways affected by oleic and palmitic acid and
suggest a mechanism of prenatal high-fat diet induced neurogenesis events is through these two
abundant fatty acids.
Keywords: hypothalamic neurons, oleic acid, palmitic acid, proliferation, apoptosis, migration
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1. Introduction
The hypothalamus is a heterogeneous brain region that regulates homeostatic processes of the body,
including energy sensing in relation to hunger and satiety [1]. There are many types of neurons in
the hypothalamus that contain a variation of neurotransmitters, neuropeptides, and receptors that
control these homeostatic processes [2]. While the ingestion of a high-fat diet in adult animal
models change the expression patterns of these neuronal regulators in the hypothalamus [3, 4],
exposure to these diets during pregnancy has been widely accepted to program offspring to be
more prone to ingesting these diets and becoming obese [5, 6]. Neuronal prenatal programming by
a high-fat diet includes epigenetic changes [7], increased neurogenesis of orexigenic neuropeptides
[6, 8], increased inflammation [9, 10], and altered neuronal patterning and connections to other
brain regions [11] and to the gut [12]. The molecular mechanisms leading to these developmental
changes while widely studied are still under speculation.
A large component of high-fat diets used in animal model studies is the saturated fatty acid,
palmitic acid, and the monounsaturated fatty acid, oleic acid, which respectively constitutes 29%
and 49% of these diets [13, 14]. These two fatty acids can promote cell proliferation and
differentiation both within and outside of the central nervous system [15, 16]. The ingestion of a
high-fat diet during pregnancy also increases availability of fatty acids in the placenta and to the
embryo itself [17, 18]. Thus, it is possible that HFD ingestion during pregnancy increases the
availability of fatty acids to the developing embryonic brain. The highly concentrated neural
progenitor cell population may be disturbed by the overabundance of fatty acids and lead to
changes in neurogenesis events, consequently producing hyperphagic offspring. To better examine
the direct effect of fatty acids on neurodevelopmental processes, this study utilizes an immortalized
rat embryonic hypothalamic neuronal cell line to examine differential gene expression changes
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caused by oleic and palmitic acid. The findings reveal several changes in pathways relating to the
cell cycle, proliferation, apoptosis, and migration, in addition to other endocrine related processes.
Further examination of hypothalamic neurons shows low concentrations of oleic acid to stimulate
proliferation and high concentrations of oleic and palmitic acid to stimulate cell death while
inhibiting migration. These results provide potential cellular pathways that may be involved in the
effects of a high-fat diet through oleic and palmitic acids on distinct aspects of hypothalamic
neurodevelopment.
2. Methods
2.1 Cell culture. Immortalized embryonic day 18 (E18) hypothalamic rat neurons (rHypoE-9) were
acquired from Cedarlane (Burlington, NC). Neurons were maintained in culture using 10% FBS
in 1X DMEM supplemented with 1X penicillin/streptomycin (Thermofisher Scientific, Waltham,
MA). Cells were placed in a humidified 5% CO
2
incubator at 37°C. Cells were passaged every 3-
4 days when the confluency reached ~95%. Fatty acids (Sigma-Aldrich, St. Louis, MO) were
dissolved in 100% ethanol at 1000x’s the usable concentration and diluted immediately prior to
use, as previously described [14, 19, 20].
2.2 RNA-seq. The hypothalamic neurons were treated with 1, 10, and 100 M oleic acid or palmitic
acid for 24 hours prior to experimentation (n = 3), as previously described [14]. Cell culture
samples were collected with RNAprotect Cell Reagent (Qiagen, Germantown, MD) and the
mRNA was extracted using a Qiagen RNeasy kit (Qiagen, Germantown, MD), as previously
described [21]. The yield was initially quantified with a Nanophotometer (Implen, Germany), with
resulting ratios of absorbance at 260 to 280 nm of total RNA from all samples ranging between
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1.90 and 2.10, indicating high purity. The mRNA samples were sent to Genewiz (South Plainfield,
NJ) to determine RNA integrity (RIN > 9.9 for all samples), library preparation, quantification and
quality control analysis. Genewiz also performed RNA sequencing with polyA selection using
Illumina HiSeq 2x150 bp single index sequencing. Sequencing yielded libraries with an average
of 34 million reads. Data was returned in FastQ formats on an external hard drive. The data analysis
was performed utilizing Seawulf HPC at Stony Brook University.
2.3 Transcriptome Data Analysis. The RNAseq analysis was first aligned and annotated to the
Rattus Norvegicus Rnor 6.0 genome using STAR v2.7.6 [22] with default settings. The output
“.bam” files were then quantified using Stringtie v2.1.4 [23] to estimate transcript abundances as
FPKM (Fragments Per Kilobase of exon per Million fragments mapped) which normalizes
transcript expression for transcript length and the total number of sequence reads per sample. The
reads were first quantified to the Rnor 6.0 reference annotation sequences, merged and requantified
to the global merged transcripts. Following this, the reads were analyzed in R using DEseq2 v3.12
[24] to determine differential expression across all treatment groups. Over 90,000 genes were
aligned and quantified across all experimental condition.
Gene expression analysis was performed across all concentrations of palmitic and oleic acids
using Genesis [25] to select genes that were differentially expressed. The data was transformed to
Log2 fold change and using 1 – Pearson correlation metric and were hierarchically clustered (HCL)
for differences in expression as a function of the fatty acid or genes. To understand the biological
meaning of the differentially expressed genes, the resulting gene IDs was loaded into Panther
(http://www.pantherdb.org) or ENRICHR (https://maayanlab.cloud/Enrichr/) for Gene Ontology
(GO) enrichment analysis. To further classify the pathways affected by each individual fatty acid
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The copyright holder for this preprintthis version posted August 4, 2021. ; https://doi.org/10.1101/2021.08.03.454666doi: bioRxiv preprint