CLN3 Protein Involved in Maintaining Water Balance, Batten Disease Model Shows

CLN3, the protein lacking in the juvenile form of Batten disease (CLN3 disease), is involved in maintaining water balance, which is key for cell survival and growth, according to a recent study.

Findings from the study also highlight a link between CLN3 and CLN2 — a protein that, when mutated, causes CLN2 disease, a late-infantile form of Batten disease — to regulate water balance.

The study, “Cln3 function is linked to osmoregulation in a Dictyostelium model of Batten disease,” was published in the journal Biochimica et Biophysica Acta – Molecular Basis of Disease.

CLN3 disease is the most common form of Batten disease and is caused by mutations in the CLN3 gene, which provides instructions to make a protein called CLN3, or battenin.

While the biological function of CLN3 remains unclear, studies in mammalian cells and models have shown that CLN3 is involved in cellular osmoregulation and in kidney control of water balance.

Osmoregulation consists of the physiological processes that a cell or an organism uses to maintain water balance — compensating for water loss or avoiding excess water gain caused by osmotic stress, or sudden changes in the concentration of molecules around a cell — which is crucial for health and life.

It has been suggested that the role of CLN3 in maintaining water balance is associated with regulating the transport of molecules into or out of the cell as part of osmoregulatory responses.

Researchers at Trent University in Ontario, Canada, further evaluated the role of CLN3 in osmoregulation, using the Dictyostelium model of CLN3 disease (which lacks the CLN3 gene).

Dictyostelium discoideum, a soil microbe that has been used as a non-animal model for studying the function of proteins associated with human neurologic disorders — including Batten disease — has a very efficient osmoregulatory system that allows it to survive periods of intense rainfall and drought.

Researchers found that, in normal conditions, CLN3 localizes in the microbe’s osmoregulatory system during cell division — the process by which a parent cell divides and produces two identical daughter cells — and that CLN3 absence impairs correct cell division, or growth.

This model of CLN3 disease showed deficient osmoregulatory responses to osmotic stress, which ultimately affected cell survival and development.

Further analysis revealed that this osmoregulation dysfunction was associated with changes in the expression of genes involved in development, protein degradation, and fat metabolism. Gene expression is the process by which the genetic instructions within a gene are used to produce a protein.

The levels of expression of genes containing the instructions to produce proteins involved in the transport of molecules during osmoregulatory responses were also affected. This suggests that this type of transporter protein “may provide a novel therapeutic target for CLN3 disease, specifically with regards to the role of CLN3 in osmoregulation,” the researchers wrote.

The team also found that the levels and enzymatic activity of CLN2, or TPP1 — the enzyme lacking in CLN2 disease — were increased in the CLN3 disease model upon osmotic stress, compared with that of normal Dictyostelium. This was in accordance with previous studies showing that CLN2 activity was higher in brain samples from patients with CLN3 disease.

Researchers noted that “these findings provide further support for the molecular networking of NCL proteins in Dictyostelium as well as other organisms,” and that the interaction between CLN3 and CLN2 “can now be further explored in other genetic models of CLN3 disease.”

“This study provides new insight into the molecular pathways underlying the function of Cln3 in Dictyostelium and shows that the role of CLN3 in osmoregulation is evolutionarily conserved,” they concluded.