RS 2247911 polymorphism of GPRC6A gene and serum undercarboxylated-osteocalcin are associated with testis function

The Role of Bone-Derived Osteocalcin in Testicular Steroidogenesis: Contributing Factor to Male Fertility

Osteocalcin (OCN), a protein predominantly produced by osteoblasts in bone, has emerged as a significant factor in bone metabolism and reproductive function. This article reviews the latest research on the role of OCN beyond its traditional functions in bone mineralisation, particularly its influence on testicular steroidogenesis and male fertility. The structure and modifications of OCN are elaborated upon, highlighting its uncarboxylated form (ucOCN), which is becoming increasingly recognised for its bioactive properties. The impact of OCN on bone quantity, quality and strength is summarised, emphasising its role as a regulator of bone metabolism. Furthermore, the influence of ucOCN on testicular steroidogenesis and the involvement of GPRC6A, a G protein-coupled receptor, in mediating these effects are also explored. Evidence suggests that ucOCN regulates testosterone synthesis and spermatogenesis, which indirectly have the potential to influence bone metabolism integrity. In conclusion, OCN, particularly in its uncarboxylated form, plays a crucial role in bone metabolism and male fertility by regulating testicular steroidogenesis, with GPRC6A mediating these effects, thereby linking bone health and reproductive functions.

Osteocalcin improves testicular morphology but does not ameliorate testosterone synthesis signaling in azoospermic mice

OBJECTIVE

Osteocalcin (OCN) influences spermatogenesis in conjunction with testosterone and estrogen. OCN facilitates the secretion of testosterone by engaging with G protein-coupled receptor class C group 6 member A (GPRC6A) on Leydig cells and with androgen receptors on Sertoli cells.

METHODS

Adult mice were assigned to the following groups: control; sham I, which received dimethyl sulfoxide for 5 weeks followed by phosphate-buffered saline for 1 month; azoospermia, which was treated with busulfan (40 mg/kg); sham II, which consisted of azoospermic animals that received phosphate-buffered saline for 1 month beginning at the 5-week mark; and the experimental group, which included azoospermic mice treated with OCN (3 ng/g/day) for 1 month.

RESULTS

In the mice receiving OCN treatment, immunohistochemical analysis revealed increased expression of androgen receptors and GPRC6A, indicative of enhanced spermatogenesis. Additionally, the expression levels of the cyclic adenosine monophosphate-responsive element binding protein 1, steroidogenic acute regulatory protein, and cytochrome P450 family 11 genes were elevated. However, testosterone levels exhibited no significant differences across groups. Morphometric analysis suggests that OCN may play a crucial role in spermatogenesis, as evidenced by its positive effects on germinal cells and the germinal epithelium in the azoospermia group (p<0.05).

CONCLUSION

We conclude that OCN may serve as a beneficial therapeutic agent for male infertility.

Emerging Role of Non-collagenous Bone Proteins as Osteokines in Extraosseous Tissues

Bone is a unique tissue, composed of various types of cells embedded in a calcified extracellular matrix (ECM), whose dynamic structure consists of organic and inorganic compounds produced by bone cells. The main inorganic component is represented by hydroxyapatite, whilst the organic ECM is primarily made up of type I collagen and non-collagenous proteins. These proteins play an important role in bone homeostasis, calcium regulation, and maintenance of the hematopoietic niche. Recent advances in bone biology have highlighted the importance of specific bone proteins, named "osteokines", possessing endocrine functions and exerting effects on nonosseous tissues. Accordingly, osteokines have been found to act as growth factors, cell receptors, and adhesion molecules, thus modifying the view of bone from a static tissue fulfilling mobility to an endocrine organ itself. Since bone is involved in a paracrine and endocrine cross-talk with other tissues, a better understanding of bone secretome and the systemic roles of osteokines is expected to provide benefits in multiple topics: such as identification of novel biomarkers and the development of new therapeutic strategies. The present review discusses in detail the known osseous and extraosseous effects of these proteins and the possible respective clinical and therapeutic significance.

Osteocalcin: A Multifaceted Bone-Derived Hormone

Together, loss- and gain-of-function experiments have identified the bone-derived secreted molecule osteocalcin as a hormone with a broad reach in rodents and primates. Following its binding to one of three receptors, osteocalcin exerts a profound influence on various aspects of energy metabolism as well as steroidogenesis, neurotransmitter biosynthesis and thereby male fertility, electrolyte homeostasis, cognition, the acute stress response, and exercise capacity. Although this review focuses mostly on the regulation of energy metabolism by osteocalcin, it also touches on its other functions. Lastly, it proposes what could be a common theme between the functions of osteocalcin and between these functions and the structural functions of bone.