Waste-Management Consultant

By audaciously pursuing an abandoned area of research, Ana María Cuervo discovered how cells selectively break down their waste, and revealed the health consequences when that process malfunctions.

By | November 1, 2013

Robert and Renee Belfer Chair for the Study
   of Neurodegenerative Diseases
Professor of Developmental and Molecular Biology Albert Einstein College of Medicine
Bronx, New York
As a medical student, Ana María Cuervo assumed that students in her class who got top scores on the second-year exam would get their pick of research opportunities, so she studied hard, aced the test, and identified a biochemistry laboratory she wanted to join. Only then did she find out her assumption was wrong: lower-scoring students had a choice; top exam scorers were assigned to labs.

It was 1986 at the University of Valencia in Spain, and Cuervo was placed in a lab studying nerve conduction. “Nobody wanted to go into that lab,” says Cuervo. “I thought, ‘Oh my god, I’m going to be putting electrodes into the tails of rats. How uncool is that?’”

But today, Cuervo looks back on that moment as a positive turning point in her career. The head of the lab, Joaquín Romá, became Cuervo’s first mentor and fueled her devotion to research. “He taught us to formulate a question and test it, but the answer wasn’t the important part,” she says. Since Cuervo was addicted to Diet Coke, for example, Romá had her perform a study on the effect of caffeine on nerve conduction. Cuervo stayed in Romá’s laboratory for the rest of her four-year stint in medical school. “By then, I knew I wanted to do research full-time,” she says.

By another twist of fate, Cuervo soon began to study autophagy—the process by which cells break down their waste inside organelles called lysosomes. It was once again an “uncool” area of research, yet Cuervo went on to make groundbreaking discoveries in the field, including alterations in lysosomal protein degradation that are associated with neurodegenerative diseases, and the ways that autophagy protects against aging.

Here, Cuervo happily remembers trying to avoid studying lysosomes, running a lab by herself as a postdoc when her advisor went blind, and convincing her husband to write a grant on autophagy with her.

Cuervo Calling

Ana María, MD. “I was born and raised in Barcelona, and then went to medical school in Valencia. When I had to register for college, I initially decided to do biology, and was mainly attracted to human biology. So I went home and told my mom I was going into medicine. She said, ‘Okay. . . . But, Ana María, do you remember that you faint when you see blood?’ That was true. But I told her I would just explore medicine and maybe get into research.”

“[Erwin Knecht] said, ‘Oh my god, you don’t even know what a lysosome is?’ and made me . . . read Bruce Alberts’s Molecular Biology of the Cell all the way through.”

Lucky error. In Romá’s lab at the University of Valencia, Cuervo found her calling in research rather than medicine. After finishing her MD in 1990, she then spent another four years completing a PhD in biochemistry and molecular biology in the lab of Erwin Knecht at the Instituto de Investigaciones Citológicas, also in Valencia. “I ended up with him by mistake. When I visited the institute, they mentioned a lab working in aging.” In medical school, Cuervo had done a rotation in geriatrics and felt frustrated that all that was available for seniors was palliative care—no prevention and few treatments—so she wanted to study the mechanisms of aging. “What I didn’t realize is that two labs were working in aging, so when I called to interview with the PI who worked in mitochondria and aging, he happened to not be there that day, but they told me Erwin Knecht was there and he also worked in aging. He was working in lysosomes. And that’s what I’ve been doing ever since. It was probably one of the best ‘mistakes’ of my life.”

Ye of little faith. “There was a lot of drama when I joined his lab,” Cuervo recalls with a smile. It was 1991 and Knecht’s lab had long studied lysosomes, but its focus was shifting to the next big thing in protein degradation—the proteasome, a non-membrane-bound enzyme complex in the cytoplasm. Cuervo, however, was not included in that shift. “The only reason why I think I got stuck on [lysosomes] was because he didn’t like MDs and hadn’t had one in his lab [before], so I don’t think he had much faith that I was going to make it. And I don’t blame him, because my biochemistry and cell biology background was as minimal as one could have. He said, ‘Oh my god, you don’t even know what a lysosome is?’ and made me sit down for a month and read Bruce Alberts’s Molecular Biology of the Cell all the way through. It’s a very thick book.”

Selective start. Within a couple of months, Knecht realized Cuervo’s dedication and determination, and the two soon spent hours discussing molecular biology. Under Knecht’s mentorship, in 1993 Cuervo published her first paper on lysosomes, which challenged the commonly held belief that lysosomal degradation is nonselective—that lysosomes indiscriminately trap and degrade nearby proteins at the same rate. The study showed that lysosomes selectively degrade a glycolytic enzyme called GAPDH.

Study abroad. In Spain, universities used to close their laboratories for the summer, Cuervo recalls. “It was really disruptive. You had to plan your experiments to sacrifice all your animals before the summer, because there was going to be no one to care for them.” Luckily, the government offered fellowships to send PhD students abroad to work in July and August. Knecht called J. Fred “Paulo” Dice at Tufts University, who had recently published a paper on selective protein degradation in a different model system—fibroblasts instead of liver cells—and asked Dice to take Cuervo for the summer. “Fred said, ‘And I don’t have to pay for her? Sure.’ So he took me for a summer and I learned to isolate lysosomes from cells using his method and looked at if the two systems we were studying were the same.” They soon concluded that the same selective lysosomal degradation pathway was used in both systems, even when breaking down completely different proteins.

Leaving lysosomes? After Cuervo completed her thesis, “there was a general agreement that I should forget about lysosomes,” she says. “We were getting some nice papers, but proteasomes were the big thing and they thought I should learn about another area. Even my mother said I had to leave lysosomes. But I wanted to go back to Boston and Tufts, so Fred said I could come there for a couple months and finish a paper, and then I could look for a postdoc anywhere in the States that I wanted to go, in any topic. But my plan didn’t work very well.” Cuervo joined Dice’s lab as a postdoc in 1995, and she stayed for six years.

Blind devotion. When Cuervo first joined Dice’s lab, he had 10 lab members. But six months later, due to complications of diabetes, Dice began to lose his eyesight, and the lab’s funding and activity decreased. Eventually, the lab shrank way down in size. “He offered to find me a postdoc position elsewhere, but I said, ‘Are you kidding? Lysosomes just got interesting!’” Cuervo had identified what she believed to be a receptor for the selective degradation pathway, and, because of her training, was able to continue her project with Dice’s intellectual contribution from a distance when he was not able to come to the lab. “We talked a lot by phone every day—not only about experiments. He also helped with my application for a K01 career award.”

Desperately seeking Science. Cuervo won the K01 grant, and used it to identify lysosomal membrane glycoprotein LGP96 as the receptor for the selective import and degradation of proteins within lysosomes. “My English sucked, but I always insisted on writing the drafts of my papers. I remember Paulo said he was going to write this one because he wanted to send it to Science. I wondered why he was wasting his time. But Science wanted it, and it was one of the fastest-accepted papers of my career. I couldn’t believe it. From then on, I wanted to send everything to Science. Of course, it didn’t happen again until 10 years later.” In 2000, Cuervo and Dice named their pathway chaperone-mediated autophagy, CMA for short, and demonstrated that CMA declines in aging rats. “Many years later, the editor of Autophagy asked if we chose the name because it was my initials backwards. It became a joke that ‘AMC was studying CMA.’ I had looked at it for years and never noticed.”

Cuervo Takes Command

Home alone. In 2001, Cuervo accepted a faculty position at Albert Einstein College of Medicine in the Bronx, New York. She decided to focus her lab on human disease and biomedical aspects related to CMA. “I moved there on October 1, 2001, and after September 11 that year, most visas were frozen. I had students in China and India coming to do their theses with me and a postdoc in Europe, but they couldn’t come, so I had an empty lab for the first year.”

Receptor replacement. Once Cuervo’s students arrived, her work took off. “The idea was to continue studying the basic biology of lysosomes and the changes as we age.” In her 2000 paper with Dice, Cuervo had shown that levels of autophagy decrease as mammals age because the levels of the receptor—originally called LGP96 but soon renamed LAMP-2A—decrease. Her team then created a transgenic mouse model in which the disappearing receptors could be replaced as the animals aged. Using the model, the researchers showed that if the activity of CMA is preserved by maintaining LAMP-2A activity, animals fare better, with less protein damage and better liver function. “It’s unlikely we’ll be doing gene therapy like this for humans, but at least it gave us the rationale of why we want to enhance this pathway to prevent the complications of aging.”

Complex-ity. Another focus of Cuervo’s lab is the basic mechanism of how proteins are translocated across the lysosomal membrane. “The LAMP-2A receptor is a monomeric membrane protein, but as soon as a substrate binds to it, it multimerizes and forms a complex. We’ve been trying to figure out how that complex forms.” In 2010, she published evidence of the first regulators of this process: glial fibrillary acidic protein, or GFAP, stabilizes the complex, while GTP, a molecule involved in energy transfer in cells, promotes disassociation of the complex through a second regulatory protein, EF1α. The finding presented new therapeutic targets for upregulating CMA activity.

“We’ve come to think that compromised chaperone-mediated autophagy may be a common theme across neurodegenerative diseases.”

Breaking down disease. Cuervo did eventually return to her medical roots, and has made numerous discoveries linking impaired CMA with age-related disease. In collaboration with Columbia University’s David Sulzer, Cuervo presented evidence of altered CMA in Parkinson’s disease in 2004, and then in 2010 demonstrated that inefficient cargo loading of proteins into lysosomes could be responsible for the pathogenic accumulation of proteins inside cells of Huntington’s patients. This year, her team also demonstrated that LRRK2, one of the proteins mutated in Parkinson’s disease, disrupts the formation of LAMP-2A translocation complexes in the lysosomal membrane. “We’ve come to think that compromised chaperone-mediated autophagy may be a common theme across neurodegenerative diseases. If we could improve or even just compensate for the age-dependent decline, we might be able to slow down the course of disease.”

Cancer coup. Recently, Cuervo strayed into oncology with a discovery that CMA is required for tumor growth. “It was amazing. In almost all of the 17 different [tumor] cell types that we tried, CMA was enhanced. So then we blocked it, and the tumors shrank. It was a first report that we are following up. And now in our work screening for compounds, we’re looking not just for [CMA] activators for diseases like Parkinson’s, but inhibitors for cancer.”

Cuervo Considers

Love at second sight. “My husband and I went to the same med school and apparently we met in the first year, but I don’t remember him until the second year because we were chosen for Joaquín Romá’s lab together. I published my first paper with him. I was rather nerdy and not much into romance, but we started doing experiments together, going to conferences together, and eventually, you know, started dating.”

Family affairs. Today, Cuervo’s husband, Fernando Macian, runs an immunology lab at Einstein. “We are in different departments in different buildings but on the same floor, so we just have to cross a bridge to see each other. And I convinced him to start a side project on autophagy in the immune system, so we now have a grant on autophagy and aging related to stress. After so many years of us being together, now he’s calling me during the day to ask, ‘So about the lysosomal membrane, how does it work?’”

Freedom of flight. “Maybe it’s in my genes, because my father used to be a pilot, but I love flying and traveling. I can organize my time better. When you travel, there might be a delay, but that’s my time to read and write. I can concentrate. Now, if I don’t travel in a month, my students ask when I’m traveling again to find out when I’ll finish their papers.” 

Greatest Hits

  • With Erwin Knecht, demonstrated that lysosomal degradation of proteins can be selective.
  • With Fred Dice, identified the membrane receptor for chaperone-mediated autophagy (CMA).
  • Elucidated the molecular mechanisms by which proteins are translocated across the lysosomal membrane in CMA.
  • Uncovered numerous examples of defective autophagy in neurodegenerative diseases, including Huntington’s, Parkinson’s, and Alzheimer’s disease.
  • Showed that CMA is upregulated in cancer cells, and that blocking it can prevent tumor growth.

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