A Japanese researcher at the center of research initially hailed as a breakthrough for stem cell treatment killed himself after months of stress and exhaustion, officials said on Tuesday.
Yoshiki Sasai, 52, was the co-author of the high-profile research that had seemed to offer hope for replacing damaged cells or even growing new human organs. The work was discredited after months of controversy that made front-page news in Japan and tarnished the country's reputation for scientific research.
Sasai was found dead early on Tuesday at the RIKEN institute where he worked in Kobe, Japan, police and the institute said.
"It is confirmed as a suicide," said a police spokesman. "It was a hanging."
A security guard found him suffering from cardiac arrest, with a rope around his neck, according to RIKEN. Sasai was rushed to a hospital but was pronounced dead two hours later.
As deputy director of the RIKEN Center for Developmental Biology, Sasai supervised the work of lead author Haruko Obokata. The work took the world of molecular biology by storm when it was published in the British journal Nature in January.
Obokata was "very shocked" at Sasai's suicide, Kagaya said.
Sasai started receiving counseling in April and recently had trouble communicating due to side-effects of medical treatments he was undergoing, local media reported.
Public broadcaster NHK said three letters that appeared to be suicide notes were found in a bag next to his body. Each one was addressed to Haruko Obokata, a co-author of the research papers, as well as other senior members of the research center.
In the letters, Sasai asked Obokata to prove the existence of cells that could be easily transformed into highly versatile stem cells — the subject of their now discredited research.
Sasai's team retracted the research papers from British science journal Nature over Obokata's alleged malpractice, which she has contested. Retractions of papers in major scientific journals are extremely rare.
RIKEN later held Obokata responsible for falsifying data. The investigation also focused on Sasai and two other employees, though the three were not accused of research misconduct.
Sasai had been hospitalized in March for stress and become less receptive to media inquiries during the controversy over the team's research, RIKEN spokesman Satoru Kagaya said.
The scientist "had seemed completely exhausted" in their last phone conversation around May or June, Kagaya told a televised news conference.
The journal's editor-in-chief, Phil Campbell, issued a statement in London describing Sasai's death as a true tragedy for science and an immense loss to the research community.
"Yoshiki Sasai was an exceptional scientist, and he has left an extraordinary legacy of pioneering work across many fields within stem cell and developmental biology," Campbell said.
Japan's top government spokesman, Chief Cabinet Secretary Yoshihide Suga, said the suicide was "very unfortunate."
"Mr Sasai contributed greatly in the field of developmental biology and was an internationally renowned researcher."
In what looked like a game-changing discovery, Obokata, Sasai and the other authors described simple ways to reprogram mature animal cells back to an embryonic-like state, allowing them to generate many different types of cells.
But questions soon arose about the research, as other scientists could not replicate the startling claims. RIKEN said its investigation found Obokata had plagiarized and fabricated parts of the papers.
After defending her work for months against RIKEN’s claims, Obokata agreed in June to retract the papers, which Nature did in early July.
Despite the retractions of the research papers, Sasai said he never wavered in his belief that Stimulus-Triggered Acquisition of Pluripotency, or STAP, cells could exist, Japanese media said.