Breaking the Rules – Important Molecular Pathway for Control of Aging Discovered

Research on the roundworm species C. elegans has demonstrated that disruptions in the transfer of RNA between cells across various tissues can lead to a shortened lifespan.

Cells in various tissues interact by sharing RNARibonucleic acid (RNA) is a polymeric molecule similar to DNA that is essential in various biological roles in coding, decoding, regulation and expression of genes. Both are nucleic acids, but unlike DNA, RNA is single-stranded. An RNA strand has a backbone made of alternating sugar (ribose) and phosphate groups. Attached to each sugar is one of four bases—adenine (A), uracil (U), cytosine (C), or guanine (G). Different types of RNA exist in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>RNA molecules. A study conducted by scientists from the State University of Campinas (UNICAMP) in Brazil, using the roundworm speciesA species is a group of living organisms that share a set of common characteristics and are able to breed and produce fertile offspring. The concept of a species is important in biology as it is used to classify and organize the diversity of life. There are different ways to define a species, but the most widely accepted one is the biological species concept, which defines a species as a group of organisms that can interbreed and produce viable offspring in nature. This definition is widely used in evolutionary biology and ecology to identify and classify living organisms.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>species Caenorhabditis elegans, discovered that disruptions in this method of communication can lead to a reduced lifespan for the organism. The study was recently published in the journal Gene. The findings contribute to a better understanding of the aging process and associated diseases.

“Previous research showed that some types of RNA can be transferred from one cell to another, mediating intertissue communication, of the kind that occurs with proteins and metabolites, for example. This is considered a mechanism for signaling between organs or neighboring cells. It’s part [of the physiopathology] of several diseases and of the organism’s normal functioning,” said Marcelo Mori, corresponding author of the article and a professor at the Institute of Biology (IB-UNICAMP). “What wasn’t clear and we’ve now succeeded in proving is that changes in the pattern of this ‘conversation’ between RNA molecules can affect aging.”

The study was conducted at UNICAMP’s Obesity and Comorbidities Research Center (OCRC), one of the Research, Innovation, and Dissemination Centers (RIDCs) funded by FAPESP. It was also funded via a project for which Mori is the principal investigator.

“This communication mechanism has to be well adjusted to give the organism an adequate lifespan. In the study, we found that if any tissue happens to increase its capacity to absorb some types of RNA from the extracellular medium, this ends up having an impact on the organism’s lifespan,” Mori said.

The researchers demonstrated that the reduction in lifespan was due not only to the disruption of RNA-based communication between tissues in the same organism, he added, but also to an increase in the capacity for RNA uptake from the environment – bacteria in microbiota, for example. As they explain in the article, “Our data support the notion that systemic RNA signaling must be tightly regulated, and unbalancing that process provokes a reduction in lifespan. We termed this phenomenon Intercellular/Extracellular Systemic RNA imbalance (InExS).”

Breaking the rules

Mori explained that the decision to research the intercellular RNA transport mechanism was inspired by the discovery of RNA interference, for which American scientists Andrew Fire and Craig Mello won the 2006 Nobel Prize in Physiology and Medicine. They injected double-stranded RNA into C. elegans to “silence” genes with great precision. “They found that the silencing mechanism affected genes in other tissues as well as the tissue involved and that it was transmitted to following generations,” he said.

The discovery of RNA interference elucidated the mechanisms underlying RNA transfer between cells in an organism and between the organism and the environment. It also relativized a central dogma of molecular biology. Until then, the information embodied by the genetic code was believed to flow only from DNADNA, or deoxyribonucleic acid, is a molecule composed of two long strands of nucleotides that coil around each other to form a double helix. It is the hereditary material in humans and almost all other organisms that carries genetic instructions for development, functioning, growth, and reproduction. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>DNA to RNA, and from there to proteins, but the work of Fire and Craig revealed that double-stranded RNA can block this flow. Messenger RNA is destroyed by RNA interference, which silences specific genes without altering the DNA sequence, showing that RNA can also perform a regulatory function in the genome. Although the human genome comprises some 30,000 genes, only a few are used in each cell to synthesize proteins. A large proportion play a regulatory role, influencing the expression of other genes.

Balance is all

“We wanted to understand how this process could interfere with important physiological functions linked to aging. In C. elegans, RNA transfer between cells involves what are known as systemic RNA interference defective (SID) genes [responsible for different stages in RNA absorption and export]. We observed that a gene expression pattern associated with this pathway in specific tissues changed during aging. The messenger RNA that encodes the protein SID-1 [fundamental to cellular uptake of RNA], for example, increased in some tissues and decreased in others,” Mori said.

To find out more about the role of RNA in intertissue signaling, the researchers conducted experiments in which they manipulated the expression of the protein SID-1 in specific tissues of C. elegans, such as neuronal, intestinal, and muscle cells, in order to change its function.

“We found mutants without the SID-1 function to be as healthy as wild-type worms, whereas overexpression of SID-1 in the gut, muscles, or neurons shortened the lifespan of the worms concerned. We also found that a lifespan reduction correlated with overexpression of other proteins in the RNA transport pathway, such as SID-2 and SID-5,” he said.

The dysregulation may reside in the distribution of RNA to tissue. “To dysregulate RNA distribution in the worms, we increased SID-1 expression in specific tissues [gut, muscles, and neurons] and found that channeling it to a specific organ led to a lifespan reduction,” he said.

“We also showed that this imbalance in RNA transfer led to loss of function in the pathway that produces microRNAs [small pieces of non-coding RNA with a regulatory function]. It’s as if the larger number of RNAs transported to these tissues created a kind of competition in which the production of microRNAs was the loser. Previous research had already shown that loss of function in microRNA production led to a reduction of lifespan.”

The UNICAMP group also investigated exogenous RNA transfer (between the outside environment and the organism). As in the previous experiments, a reduction of lifespan correlated with overexpression of SID-2, which mediates RNA uptake from the gut, and with excessive RNA production by bacteria on which the worms feed and which end up in its gut microbiota.

“We believe the worms may use exogenous RNA to monitor microorganisms in the environment, but negative effects may ensue when excessive amounts are absorbed by their tissue,” Mori said. “When we forced bacteria in the laboratory to express more double-stranded RNA, the worms’ lifespan decreased. Excessive RNA transfer interferes with homeostasis and endogenous RNA production, accelerating the aging process.”

Reference: “Tissue-specific overexpression of systemic RNA interference components limits lifespan in C. elegans” by Henrique Camara, Mehmet Dinçer Inan, Carlos A. Vergani-Junior, Silas Pinto, Thiago L. Knittel, Willian G. Salgueiro, Guilherme Tonon-da-Silva, Juliana Ramirez, Diogo de Moraes, Deisi L. Braga, Evandro A. De-Souza and Marcelo A. Mori, 18 November 2023, Gene.
DOI: 10.1016/j.gene.2023.148014

The study was funded by the São Paulo Research Foundation.