Correlation Between Differentiation of Adrenocortical Zones and Telomere Lengths Measured by Q-FISH

Single-cell and spatial transcriptomics analysis of human adrenal aging

OBJECTIVE

The human adrenal cortex comprises three functionally and structurally distinct layers that produce layer-specific steroid hormones. With aging, the human adrenal cortex undergoes functional and structural alteration or "adrenal aging", leading to the unbalanced production of steroid hormones. Given the marked species differences in adrenal biology, the underlying mechanisms of human adrenal aging have not been sufficiently studied. This study was designed to elucidate the mechanisms linking the functional and structural alterations of the human adrenal cortex.

METHODS

We conducted single-cell RNA sequencing and spatial transcriptomics analysis of the aged human adrenal cortex.

RESULTS

The data of this study suggest that the layer-specific alterations of multiple signaling pathways underlie the abnormal layered structure and layer-specific changes in steroidogenic cells. We also highlighted that macrophages mediate age-related adrenocortical cell inflammation and senescence.

CONCLUSIONS

This study is the first detailed analysis of the aged human adrenal cortex at single-cell resolution and helps to elucidate the mechanism of human adrenal aging, thereby leading to a better understanding of the pathophysiology of age-related disorders associated with adrenal aging.

Age-related Changes in the Adrenal Cortex: Insights and Implications

Aging is characterized by a gradual decline in physiological function. This process affects all organs including the adrenal cortex, which normally functions to produce essential steroid hormones including mineralocorticoids, glucocorticoids, and androgens. With increasing age, features such as reduced adrenal cortex size, altered zonation, and increased myeloid immune cell infiltration substantially alter the structure and function of the adrenal cortex. Many of these hallmark features of adrenal cortex aging occur both in males and females, yet are more enhanced in males. Hormonally, a substantial reduction in adrenal androgens is a key feature of aging, which is accompanied by modest changes in aldosterone and cortisol. These hormonal changes are associated with various pathological consequences including impaired immune responses, decreased bone health, and accelerated age-related diseases. One of the most notable changes with adrenal aging is the increased incidence of adrenal tumors, which is sex dimorphic with a higher prevalence in females. Increased adrenal tumorigenesis with age is likely driven by both an increase in genetic mutations as well as remodeling of the tissue microenvironment. Novel antiaging strategies offer a promising avenue to mitigate adrenal aging and alleviate age-associated pathologies, including adrenal tumors.

Telomere Length in Human Spermatogenic Cells as a New Potential Predictor of Clinical Outcomes in ART Treatment with Intracytoplasmic Injection of Testicular Spermatozoa

Predicting the clinical outcomes of intracytoplasmic sperm injection (ICSI) cycles that use the testicular spermatozoa of azoospermic patients presents a challenge. Thus, the development of additional approaches to assessing the competence of a testicular-sperm-derived embryo without causing damage to gametes or the embryo is necessary. One of the key parameters in determining such developmental competence is telomere length (TL). We aimed to analyze TLs in spermatogenic cells from the testicular biopsy samples of azoospermic patients and determine how this parameter influences embryo competence for pre- and post-implantation development. Using Q-FISH, we studied the TL of the chromosomes in spermatogonia and spermatocytes I from the TESE biopsy samples of 30 azoospermic patients. An increase in TL was detected during the differentiation from spermatogonia to spermatocytes I. The patients' testicular spermatozoa were used in 37 ICSI cycles that resulted in 22 embryo transfers. Nine pregnancies resulted, of which, one was ectopic and eight ended in birth. The analysis of embryological outcomes revealed a dependence between embryo competence for development to the blastocyst stage and the TL in spermatogenic cells. The TLs in spermatogonia and spermatocytes I in the testicular biopsy samples were found to be higher in patients whose testicular sperm ICSI cycles resulted in a birth. Therefore, the length of telomeres in spermatogenic cells can be considered as a potential prognostic criterion in assessing the competence of testicular-sperm-derived embryos for pre- and post-implantation development. The results of this study provide the basis for the development of a laboratory test for the prediction of testicular sperm ICSI cycle outcomes.

Cellular Senescence in Adrenocortical Biology and Its Disorders

Cellular senescence is considered a physiological process along with aging and has recently been reported to be involved in the pathogenesis of many age-related disorders. Cellular senescence was first found in human fibroblasts and gradually explored in many other organs, including endocrine organs. The adrenal cortex is essential for the maintenance of blood volume, carbohydrate metabolism, reaction to stress and the development of sexual characteristics. Recently, the adrenal cortex was reported to harbor some obvious age-dependent features. For instance, the circulating levels of aldosterone and adrenal androgen gradually descend, whereas those of cortisol increase with aging. The detailed mechanisms have remained unknown, but cellular senescence was considered to play an essential role in age-related changes of the adrenal cortex. Recent studies have demonstrated that the senescent phenotype of zona glomerulosa (ZG) acts in association with reduced aldosterone production in both physiological and pathological aldosterone-producing cells, whereas senescent cortical-producing cells seemed not to have a suppressed cortisol-producing ability. In addition, accumulated lipofuscin formation, telomere shortening and cellular atrophy in zona reticularis cells during aging may account for the age-dependent decline in adrenal androgen levels. In adrenocortical disorders, including both aldosterone-producing adenoma (APA) and cortisol-producing adenoma (CPA), different cellular subtypes of tumor cells presented divergent senescent phenotypes, whereby compact cells in both APA and CPA harbored more senescent phenotypes than clear cells. Autonomous cortisol production from CPA reinforced a local cellular senescence that was more severe than that in APA. Adrenocortical carcinoma (ACC) was also reported to harbor oncogene-induced senescence, which compensatorily follows carcinogenesis and tumor progress. Adrenocortical steroids can induce not only a local senescence but also a periphery senescence in many other tissues. Therefore, herein, we systemically review the recent advances related to cellular senescence in adrenocortical biology and its associated disorders.

Cellular Senescence in Human Aldosterone-Producing Adrenocortical Cells and Related Disorders

In situ cortisol excess was previously reported to promote cellular senescence, a cell response to stress, in cortisol-producing adenomas (CPA). The aim of this study was to explore senescence pathways in aldosterone-producing cells and related disorders, and the influence of aldosterone overproduction on in situ senescence. We analyzed 30 surgical cases of aldosterone-producing adenoma (APA), 10 idiopathic hyperaldosteronism (IHA) and 19 normal adrenals (NA). CYP11B2 and senescence markers p16 and p21 were immunolocalized in all those cases above and results were correlated with histological/endocrinological findings. In the three cohorts examined, the zona glomerulosa (ZG) was significantly more senescent than other corticosteroid-producing cells. In addition, the ZG of adjacent non-pathological adrenal glands of APA and IHA had significantly higher p16 expression than adjacent non-pathological zona fasciculata (ZF), reticularis (ZR) and ZG of NA. In addition, laboratory findings of primary aldosteronism (PA) were significantly correlated with p21 status in KCNJ5-mutated tumors. Results of our present study firstly demonstrated that non-aldosterone-producing cells in the ZG were the most senescent compared to other cortical zones and aldosterone-producing cells in PA. Therefore, aldosterone production, whether physiological or pathological, could be maintained by suppression of cell senescence in human adrenal cortex.

The Sexually Dimorphic Adrenal Cortex: Implications for Adrenal Disease

Many adrenocortical diseases are more prevalent in women than in men, but the reasons underlying this sex bias are still unknown. Recent studies involving gonadectomy and sex hormone replacement experiments in mice have shed some light onto the molecular basis of sexual dimorphism in the adrenal cortex. Indeed, it has been shown that gonadal hormones influence many aspects of adrenal physiology, ranging from stem cell-dependent tissue turnover to steroidogenesis and X-zone dynamics. This article reviews current knowledge on adrenal cortex sexual dimorphism and the potential mechanisms underlying sex hormone influence of adrenal homeostasis. Both topics are expected to contribute to personalized and novel therapeutic approaches in the future.

Correlation Between Telomere Attrition of Zona Fasciculata and Adrenal Weight Reduction in Older Men

CONTEXT

Although numerous theories are reported on sex differences in longevity, the underlying biological mechanisms remain unknown. We previously reported that telomere length in the zona reticularis cells of the human adrenal cortex was significantly longer in older than that in younger subjects. However, we could not evaluate sex differences in the telomere lengths.

OBJECTIVE

To compare the telomere lengths of adrenocortical and adrenal medullar cells between men and women from infancy through older adulthood.

METHODS

Adrenal glands of 30 male (aged 0 to 100 years) and 25 female (aged 0 to 104 years) autopsied subjects were retrieved from autopsy files. Using quantitative fluorescence in situ hybridization, relative telomere lengths were determined in the parenchymal cells of the 3 adrenocortical zones and medulla. Age-related changes in the weight of adrenal glands were also investigated.

MAIN RESULTS

Older male subjects (aged 65 years or older) had significantly shorter telomere lengths in zona fasciculata (ZF) cells compared to the corresponding female subjects. In men, older subjects exhibited a significant age-related reduction in adrenal weight; however, no age-related changes in adrenal weight were detected in women.

CONCLUSION

Telomere attrition of ZF cells was correlated with adrenal weight reduction in older men but not in older women, suggesting a decreased number of ZF cells in older men. This may help us understand the possible biological mechanisms of sex difference in longevity of humans.