ARTICLE 1: An Analysis of Gene Expression Data Involving Examination of Signaling Pathways Activation Reveals New Insights into the Mechanism of Action of Minoxidil Topical Foam in Men with Androgenetic Alopecia
Stamatas GN, Wu J, Pappas A, et al. An analysis of gene expression data involving examination of signaling pathways activation reveals new insights into the mechanism of action of minoxidil topical foam in men with androgenetic alopecia.
Cell Cycle. 2017;16(17):1578-84.
Abstract
Androgenetic alopecia (AGA) is the most common form of hair loss. Minoxidil has been approved for the treatment of hair loss; however its mechanism of action is still not fully clarified. In this study, we aimed to elucidate the effects of 5% minoxidil topical foam (MTF) on gene expression and activation of signaling pathways in vertex and frontal scalp of men with AGA. We identified regional variations in gene expression and perturbed signaling pathways using in silico Pathway Activation Network Decomposition Analysis (iPANDA) before and after treatment with minoxidil. Vertex and frontal scalp of patients showed a generally similar response to minoxidil. Both scalp regions showed upregulation of genes that encode keratin-associated proteins and downregulation of integrin-linked kinase (ILK), Akt and mitogen-activated protein kinase (MAPK) signaling pathways after minoxidil treatment. This study results provide new insights into the mechanism of action of minoxidil topical foam in men with AGA.
COMMENT
The pattern of hair loss in androgenetic alopecia (AGA) can be associated with various factors, such as the differences in the levels of hormone receptors and embryologic scalp patterning.
Topical minoxidil and oral finasteride have been approved by the Food and Drug Administration (USA) for the treatment of AGA. Minoxidil is an adenosine triphosphate (ATP) sensitive potassium (K+) channel agonist as well as a vasodilator. Only one of two forms of K+-ATP channels found in human hair follicles is sensitive to minoxidil. The drug's effect seems to be connected to its presence and stops when the treatment is discontinued.
Scalp biopsies from the frontal and vertex scalp were done from the leading edge of alopecia and global hair photographs were taken before and after 8 weeks of treatment. Based on a blinded review of stereotactic photographs, patients were categorized as having either full or minimal clinical response. Microarray analysis was done using the Affymetrix GeneChip HG U133 plus 2.0. Pathway activation analysis was performed using in silico Pathway Activation Network Decomposition Analysis (iPANDA).
The analysis revealed that both genes and noncoding RNAs were differentially expressed between vertex and frontal scalp before and after treatment with MTF 5%.
Variations in gene expression in the two scalp regions before treatment were observed. Several genes, including genes induced by oxidative stress and growth factors (DUSP1 and CYR61) and noncoding RNAs, were upregulated in frontal compared to vertex scalp, while the expression of pseudogene MSL3P1 that may be involved in chromatin remodeling and regulation of transcription was decreased. These results suggest that gene expression in hair follicles in vertex versus frontal scalp of patients with AGA may not be completely identical and exhibit different molecular signatures.
In general, vertex and frontal scalp showed similar molecular response to MTF 5% treatment. The strong upregulation of keratin-associated genes in both the vertex and frontal regions was a distinctive feature of responding patients, while patients who showed minimal response to MTF 5% treatment did not exhibit a similar level of upregulation of keratin-associated genes. The expression of several noncoding RNAs was significantly decreased in both scalp regions after treatment. It should be noted that keratinization-related genes were downregulated in the frontal scalp of both responders and placebo control patients. Thus, it is not clear whether the decreased expression of late cornified envelope protein 3D (LCE3D) was caused by the MTF 5% treatment or other as yet unidentified factors.
Baseline regional variations between frontal and vertex scalp were also visible upon pathway level examination. Thus, interleukin 2 (IL-2), which is being studied in the context of alopecia areata and integrin-linked kinase (ILK), a key mediator in integrin signal transduction, were upregulated pathways identified in frontal compared to vertex scalp. The following pathways were also upregulated in frontal versus vertex scalp before treatment—Mitogen-activated protein kinase (MAPK) (facilitates the survival of dermal papilla cells), transforming growth factor β (TGF-β) (induces catagen), Janus kinase/signal transducers and activators of transcription (JAK/STAT) (prevents anagen re-entry), phosphatase and tensin homolog (PTEN) and Akt (promotes dermal papilla cells survival and anagen initiation). The downregulated pathways included IL-6), which may provoke inflammation, and Presenilin action in Notch and Wnt signaling (NCI) pathways. It has been shown that activation of Notch signaling is necessary for keratinocyte differentiation, and Wnt signaling drives hair follicle morphogenesis, hair shaft differentiation, hair cycling induction, and maintenance.
The ILK, Akt and MAPK pathways became downregulated in both vertex and frontal scalp of responders after treatment with minoxidil topical foam (MTF) 5%.
The JAK/STAT signaling and Ras pathways were downregulated in vertex scalp of patients who responded to MTF 5% treatment. JAK/STAT inhibition should promote hair growth, while Ras pathway regulates cellular proliferation, differentiation, and senescence by stimulating various parallel effector pathways.
Protein digestion and absorption pathway, which includes several collagen-encoding genes, was significantly upregulated in the frontal scalp of responders. MTF 5% treatment also caused upregulation of mechanistic target of rapamycin (mTOR) pathway in the frontal scalp region. It is known that mTOR pathway promotes hair follicle stem cells proliferation and activation, and is activated at the moment of telogen-to-anagen transition.