Pituitary neuroendocrine tumors (PitNETs) are classified as a type of intracranial tumors [2]. Patients affected by these kinds of tumors require regular check-ups by both neurosurgeons and endocrinologists [2]. PitNETs undergo different classifications, and one the most important ones is based on their size. If the tumors are larger than 10 millimeters, they are called macroadenoma, and if they are smaller than 10 millimeters, they are referred to as microadenoma [11]. In severe cases, tumors can grow up to 40 millimeters, and this type of tumor is called “Giant tumor” [4]. Another important type of classification of PitNETs is based on their effect on hormonal levels. If the tumor affects different hormonal levels, it is called a functioning tumor. Based on the cellular origin, this type can be called "prolactinoma", "somatropin" or other types [21]. On the other hand, if the tumor does not cause hormonal imbalances, it is called non-functioning. The most prevalent form of pituitary tumors is prolactinoma, followed by non-functioning ones [6], [10]. Most cases of PitNETs are sporadic and due to acquired mutations, but they are also seen in the inherited familial syndromes like Multiple endocrine neoplasia type 1 (MEN1), MEN4 and Carney complex (CNC) [23]. The prevalence of PitNETs has been estimated to be 17% in general population [16]. However, since it has a silent nature, most of the times it remains undiagnosed or diagnosed as incidental findings through annual MRI check-ups [16]. Symptoms of pituitary adenoma vary based on their size and effect on hormonal levels. For instance, in functioning tumors, different manifestations like infertility, decreased libido and osteoporosis are seen in prolactinomas, and acromegaly is a basic feature of growth hormone secreting tumors. In non-functioning tumors, different symptoms like headaches, impaired vision and apoplexy are reported [17]. Therapeutic interventions are usually not necessary, but in severe cases, hormone replacement therapy or surgical removal through transsphenoidal approach is performed [15].

Nerve growth factor (NGF) is a neurotropic factor which was firstly discovered in 1950 s [1], [9]. NGF secretion has nourishing and maintaining effects and it contributes to the maintenance of peripheral nerves system (PNS) cells, in addition to central nervous system (CNS) stability [1]. NGF exerts its functions through binding to trkANGFR and p75NTR receptors [22]. Upon binding, different cellular pathways like MAPK, ERK and PI3K signaling are activated [22]. Transcription of a variety of genes is affected by NGF, and this has led to introduction of a new signaling pathway called “NGF stimulated transcription” in Reactome database [19].

In this study, firstly, GSE51618 data series, which contains gene expression data of non-functioning pituitary tumors (invasive and non-invasive) was download from NCBI GEO, in order to analyze differentially expressed gene (DEGs). In order to find the related molecular pathway, top candidates were uploaded in Reactome database, which led to identification of NGF stimulated transcription pathway.

To confirm bioinformatics results and better understand their role in the pituitary tumor development, we selected four genes for further analysis by Real-time PCR. These genes included three protein coding genes - ARC, ID1, and SH3GL3 - as well as a long non-coding RNA (lncRNA) called myocardial infarction associated transcript (MIAT).

ARC, also known as Activity-Regulated Cytoskeleton-Associated Protein, has a crucial role in the synaptic plasticity and RNA-mediated cell-cell communication. Studies have shown that ARC expression is associated with increased chemoresistance [24].

ID1 encodes a helix-loop-helix protein that prevents various transcription factors from binding to DNA. Overexpression of ID1 has been linked to several types of cancer, and this gene is crucial for cell cycle regulation, proliferation, and tumorigenesis [25].

SH3GL3, or SH3 Domain Containing GRB2 Like 3, is believed to play a role in synaptic vesicle uncoating and is primarily expressed in the brain and testes [7]. Its expression has been associated with glioma invasion. SH3GL3 silencing has been shown to restore normal cellular features [7].

Finally, we selected MIAT for expression analysis because previous studies have demonstrated that silencing of this lncRNA leads to decreased levels of NGF in diabetic retinas [12], [20].

Overall, by analyzing the expression of these four genes, we aim to validate our bioinformatics results and gain a deeper understanding of their involvement in the pituitary tumorigenesis, particularly in relation to NGF.