Researchers in Japan have identified a previously unknown ¡°third cell¡± essential for fully regenerating hair follicles, marking a step toward potential new treatments for hair loss.

A team led by national scientific research institute Riken and Tokyo-based startup OrganTech announced Wednesday that they had successfully re-created the complete hair-growth cycle in mice by adding the newly identified cell type to two already known components of hair follicles, the tiny organs in the skin that produce hair.

The findings have been published in the journal Biochemical and Biophysical Research Communications.

The group was headed by Takashi Tsuji, a visiting senior researcher at Riken and chairperson of OrganTech, who has spent nearly two decades developing techniques to regenerate organs from adult stem cells.

Hair naturally cycles through phases of anagen (growth), catagen (transition), telogen (rest) and exogen (shedding). While scientists have previously generated hair follicle precursors in laboratory settings using two types of cells, sustaining the full cycle of shedding and regrowth outside a living body had remained out of reach.

In 2012, the researchers combined two types of cells from adult mouse whiskers ¡ª epithelial stem cells and dermal papilla cells ¡ª to generate the basis of hair follicles, and showed that transplantation of these cells could induce hair growth.

However, in those experiments, additional supporting cells from surrounding tissue joined the follicle precursors after transplantation, suggesting that other cell types are required to form a complete hair follicle.

In the Riken and OrganTech experiment, the team used a specialized cell-isolation technique to show that when around-bulge mesenchyme (ABM) cells, found near the hair follicle, are layered together with epithelial stem cells and dermal papilla cells and transplanted into engineered skin, the three cell types are able to reproduce the entire hair cycle ¡ª including repeated growth and replacement ¡ª in a laboratory setting.

The newly identified cells were found to play a critical role in triggering the transition from the resting phase to the growth phase and in promoting elongation of the follicle.

The study also shed light on how hair follicles physically extend during growth. Rather than simply pushing hair upward, the base of the follicle ¡ª known as the hair bulb ¡ª shifts downward toward the subcutaneous fat layer as the hair shaft elongates upward.

This ¡°downgrowth¡± phenomenon occurs when regeneration-supporting cells around the bulb differentiate into other cell types and drive the downward extension of the follicle¡¯s tubular structure, according to the researchers.

Current alopecia and hair-thinning treatments largely rely on drugs that slow hair loss rather than regenerate follicles. The team said harvesting regeneration-supporting cells from patients, expanding them in a culture and reintroducing them into thinning areas could form the basis of a new therapy.