Androgenetic Alopecia (AGA), characterized by progressive hair thinning and eventual baldness, represents the most prevalent form of hair loss in humans [1]. While AGA itself does not pose an immediate medical emergency condition, its psychological implications can profoundly impact patients' self-esteem and mental well-being [2]. The common pattern of baldness observed in men, referred to as the Hamilton-Norwood classification [3], is distinguished by a sequential reduction in hair density along the forehead, followed by progressive thinning and eventual loss of hair on the vertex, leaving only the parietal and occipital areas with dense hair coverage. the prevalence of AGA escalates with advancing age, albeit the rate and extent of progression vary significantly among individuals [4].
The pathogenesis of AGA is intricately linked to dysregulation of the hair cycle [5] and the consequent miniaturization of hair follicles (HF) [6, 7]. Notably, the dysregulation primarily affects hair follicle stem cells (HFSCs), contributing significantly to the pathologic manifestations of AGA [8]. During each hair cycle, active HFSCs undergo division, giving rise to various cell types within the HF during the Anagen phase [9]. Subsequently, these stem cells enter a quiescent state during the Telogen phase [10]. HFSCs in individuals affected by AGA exhibit an extended Telogen phase compared to their healthy counterparts [5], owing to differential gene expression and altered pathway functions [8]. The dysregulation of stemness is observed in other human pathologies, as well [11, 12].
AGA arises from a complex interplay of genetic predisposition, hormonal influences, environmental factors, and advancing age [13]. In elucidating the role of aging in the context of AGA, the consequential lengthening of the Telogen phase with advancing age, culminates in a reduction in hair density. This phenomenon is attributed to the diminished capacity of HFCs to initiate new hair cycles and produce hair shafts [14]. The insights provided by previous studies offer valuable context for understanding the role of specific genes—NFATC1, SIRT7, SIRT3, and PDL-1—in AGA pathogenesis.
NFATC1 has been implicated in maintaining HFSCs in the Telogen phase of the hair cycle, inducing quiescence and inhibiting hair growth [15, 16]. NFATC1 activity is controlled by some genes such as SIRT7 [17], and SIRT7 expression decreases during aging [18]. This interplay suggests a potential link between NFATC1 dysregulation and aging-related changes in HFSC activity, contributing to AGA progression.
Mitochondrial activity may also be implicated in AGA pathogenesis. SIRT3, a mitochondrial deacetylase, exhibits altered expression levels during aging, potentially leading to mitochondrial dysfunction [19]. Considering the vital role of mitochondria in cellular function, dysregulation of SIRT3 may contribute to AGA progression.
Moreover, the upregulation of PDL-1 expression during aging, along with its inhibitory role in hair growth observed in mice [20], suggests a potential mechanism by which PDL-1 dysregulation may contribute to AGA pathogenesis.
In this study, the goal is to validate experimental findings with bioinformatic analyses, thereby enhancing our understanding of the molecular mechanisms underlying AGA.
RNA-Seq technology serves as a pivotal tool for comparing gene expression profiles between different conditions, such as affected tissue in a disease state versus healthy tissue, thereby elucidating the differential regulation of genes in each condition. Among the various computational tools available for analyzing RNA-Seq data, DESeq2[21] from Bioconductor (http://www.bioconductor.org/) is widely recognized for its effectiveness and reliability [22]. Differential expression (DE) analysis, a cornerstone of RNA-Seq data analysis, facilitates the identification of genes that have different expression [23, 24].
Furthermore, DE analysis enables downstream systems biology analyses, such as gene ontology (GO) analysis, which offers valuable insights into the cellular processes that are altered between different biological conditions [25]. Additionally, DE analysis facilitates the enrichment analysis of biological pathways using resources like the Kyoto Encyclopedia of Genes and Genomes (KEGG) database [26]. Such pathway enrichment analyses provide a comprehensive understanding of the molecular pathways and networks that are perturbed in the context of the studied condition.
Our primary objective was to evaluate the expression levels of four candidate genes—NFATC1, SIRT3, SIRT7, and PDL-1—which exhibit differential expression between aged and youthful cells, between HFSCs affected by AGA and healthy HFSCs. This analysis can help us elucidate the pathogenesis of AGA at transcriptome level.