Intracrine activity involving NAD-dependent circadian steroidogenic activity governs age-associated meibomian gland dysfunction

February 2022
Lena Sasaki, Yuki Hamada, Daisuke Yarimizu, Tomo Suzuki, Hiroki Nakamura, Aya Shimada, Khanh Tien Nguyen Pham, Xinyan Shao, Koki Yamamura, Tsutomu Inatomi, Hironobu Morinaga, Emi K. Nishimura, Fujimi Kudo, Ichiro Manabe, Shogo Haraguchi, Yuki Sugiura, Makoto Suematsu, Shigeru Kinoshita, Mamiko Machida, Takeshi Nakajima, Hiroshi Kiyonari, Hitoshi Okamura, Yoshiaki Yamaguchi, Takahito Miyake & Masao Doi

Abstract

Canonically, hormones are produced in the endocrine organs and delivered to target tissues. However, for steroids, the concept of tissue intracrinology, whereby hormones are produced in the tissues where they exert their effect without release into circulation, has been proposed, but its role in physiology/disease remains unclear.

The meibomian glands in the eyelids produce oil to prevent tear evaporation, which reduces with aging. Here, we demonstrate that (re)activation of local intracrine activity through nicotinamide adenine dinucleotide (NAD+)-dependent circadian 3β-hydroxyl-steroid dehydrogenase (3β-HSD) activity ameliorates age-associated meibomian gland dysfunction and accompanying evaporative dry eye disease.

Genetic ablation of 3β-HSD nullified local steroidogenesis and led to atrophy of the meibomian gland. Conversely, reactivation of 3β-HSD activity by boosting its coenzyme NAD+ availability improved glandular cell proliferation and alleviated the dry eye disease phenotype.

Both women and men express 3β-HSD in the meibomian gland. Enhancing local steroidogenesis may help combat age-associated meibomian gland dysfunction.

Main

Hormones are synthesized by endocrine organs, secreted into blood circulation and transported to distal target tissues, where they exert their effects. However, for steroids, in addition to the major steroidogenic endocrine organs, such as gonads and the adrenal gland, extragonadal non-endocrine tissues also participate in steroid hormone synthesis via an intracrine mechanism1. The hormones are produced locally in the same tissues where they act and are metabolically inactivated before release into the circulation1,2. The concept of intracrinology was established in the 1990s; however, its exact role in physiology and disease has not been fully explored.

Meibomian gland dysfunction (MGD) is the most common cause of dry eye, with incidence increasing with age3,4. Aging induces atrophic involution of the meibomian gland, a typical sign of MGD. However, no causal therapy exists owing to the lack of knowledge on the underlying molecular mechanism5. The enzyme 3β-HSD is essential for the biosynthesis of all classes of steroid hormones6 and has been shown to be expressed in the meibomian gland in humans;7 however, the molecular subtype of 3β-HSD protein expressed in this tissue is still undefined8. Here, we show that endogenous 3β-HSD activity declines with age, leading to MGD. We explore the physiological role of 3β-HSD-mediated local intracrine activity and demonstrate its potential for treating MGD and MGD-associated dry eye disease.

Results

Age-associated meibomian gland atrophy

We performed noncontact infrared meibography of the upper and lower eyelids of young (29–35 years) and aged (61–70 years) men and women (Fig. 1a and Supplementary Fig. 1) and found a significant age-associated reduction in gland size in both upper and lower eyelids, with age-associated morphological changes, characterized by tubular shortening and thinning and gland dropout (Fig. 1a, arrow), which are atrophic features widely observed in aged humans3,4 (Fig. 1a,b and Supplementary Fig. 1). Consistently, aged mice displayed meibomian gland atrophy (Fig. 1c,d; 24 months old versus 6 months old). Morphologically, gland shortening, thinning and dropout were also observed in aged mice (Fig. 1c).