Research Article: Carbonic Anhydrase 5 Regulates Acid-Base Homeostasis in Zebrafish

Date Published: June 22, 2012

Publisher: Public Library of Science

Author(s): Ruben Postel, Arnoud Sonnenberg, Wael El-Rifai.


The regulation of the acid-base balance in cells is essential for proper cellular homeostasis. Disturbed acid-base balance directly affects cellular physiology, which often results in various pathological conditions. In every living organism, the protein family of carbonic anhydrases regulate a broad variety of homeostatic processes. Here we describe the identification, mapping and cloning of a zebrafish carbonic anhydrase 5 (ca5) mutation, collapse of fins (cof), which causes initially a collapse of the medial fins followed by necrosis and rapid degeneration of the embryo. These phenotypical characteristics can be mimicked in wild-type embryos by acetazolamide treatment, suggesting that CA5 activity in zebrafish is essential for a proper development. In addition we show that CA5 regulates acid-base balance during embryonic development, since lowering the pH can compensate for the loss of CA5 activity. Identification of selective modulators of CA5 activity could have a major impact on the development of new therapeutics involved in the treatment of a variety of disorders.

Partial Text

Maintaining proper homeostasis is essential for every living organism. Homeostatic imbalance directly affects cellular metabolism, which eventually leads to physiological defects and pathologic conditions. Carbonic anhydrases (CA) are zinc metalloenzymes that are present in prokaryotes and eukaryotes. They catalyze the reversible dehydration/hydration reaction of carbon dioxide (CO2 + H2O ↔ HCO3−+ H+) [1], [2]. CAs are involved in many physiological processes such as transport of carbon dioxide and bicarbonate between tissues, acid-base balance and biosynthetic reactions (glucogenesis, lipogenesis and ureagenesis) [3]. CAs are also important therapeutic targets, because of their involvement in various pathological conditions, such as glaucoma, obesity, some infectious diseases, cancer, epilepsy and osteoporosis [4] Therefore, many CA inhibitors and activators have been developed in order to treat these disorders [4]. Of the five different classes of CAs (α-εCA), vertebrates only express proteins of the α-CA class, which comprises 16 members that differ in their kinetic properties, tissue distribution, subcellular localization and their susceptibility to inhibitors [2], [4]–[12]. Whereas most CA isoforms are localized in the cytosol or associate with the plasma membrane, carbonic anhydrase 5 (CA5) is the only mitochondrial α-CA [13]. In mammals CA5 is encoded by two genes, CA5A and CA5B and whereas CA5A is expressed only in the liver, CA5B is widely expressed in many tissues [14]. Here we describe the mapping, cloning and characterization of a ca5 mutant zebrafish (collapse of fins, cof) and show that CA5 is involved in regulating acid-base balance during embryonic development in zebrafish.

We show that defective CA5 activity in zebrafish results in a disturbed cellular acid-base balance, which leads to the collapse of the medial fins, heart failure and eventually degeneration of the complete embryo. We show that AZA, a general CA inhibitor, can copy the phenotype caused by the ca5cof mutation in wild-type embryos, suggesting that the T839A mutation results in the loss of CA5 enzymatic activity.