Elevated propionate signalling drives Pde9a overexpression and contractile dysfunction through increased histone acetylation and propionylation

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation and Propionic Acidemia Foundation

Background

In the heart, various metabolic pathways produce the three-carbon intermediate, propionate. This metabolite has been postulated to increase histone propionylation and acetylation (via deacetylase inhibition), and therefore affect transcription. Normally, propionate levels are kept low by propionyl-CoA carboxylase (PCC), but build-up has been reported in cardiometabolic diseases. The highest levels are attained in propionic acidaemia (PA; mutations in PCC), which also serves as a model for studying propionate biology [1].

Purpose

To establish the effect of propionate on cardiac gene expression and physiology using a mouse model of elevated propionate/propionyl-CoA signalling.

Methods

Experiments were performed using either wild-type (WT) neonatal ventricular myocytes (NRVMs) treated with propionate in vitro, or the hypomorphic mouse model of PA (Pcca-/- A138T) [2]. IC-MS metabolomics was performed on methanol-extracted metabolites. RNA-sequencing was carried out on an Illumina HiSeq 4000. For chromatin immunoprecipitation (ChIP), chromatin was isolated from PFA-fixed ventricular tissue. cGMP levels were measured by the FRET-based sensor, cGi500. Ca2+ transients were imaged in isolated myocytes using FuraRed. Cine-MRI was performed in a 7 tesla MR scanner.

Results

PA mice had the metabolic signature of propionate accumulation in plasma and cardiac lysates (metabolomics). RNA-seq of ventricular lysates identified differentially expressed genes (DEGs), but the effect was more pronounced in females. Thus, subsequent experiments were performed in females. To determine which DEGs are likely a direct response to propionate, RNA-seq was performed on propionate-treated NRVMs. The most significant DEGs common to both datasets were upregulated Pde9a (cGMP-selective phosphodiesterase) and Mme (degrades natriuretic peptides). ChIP-qPCR for histone acylation in PA and WT hearts demonstrated increases in H3K27ac at Pde9a, and strikingly, increases in propionylation at Pde9a and Mme, indicating a mechanism for this transcriptional induction. Propionate-treated NRVMs show greater sensitivity of cGMP to pharmacological inhibition of PDE9A (measured by FRET), consistent with Pde9a induction. Such changes are expected to result in diastolic dysfunction [3]. Indeed, ventricular myocytes from PA mice had higher diastolic Ca2+. Cine-MRI confirmed contractile dysfunction in vivo, with PA mice manifesting increased end-systolic and end-diastolic volumes.

Conclusions

We demonstrate that cardiac elevations of the metabolic intermediate, propionate, increases histone modifications that drive transcriptional changes in the heart, including those involved in cyclic nucleotide signalling. We also present evidence for histone propionylation, which has not been described previously in the heart. Thus, using a mouse model of a rare metabolic disease, we show how propionate/propionyl-CoA signalling affects cardiac function through epigenetic changes.

Carbonic anhydrase IX as an anticancer therapy target: preclinical evaluation of internalizing monoclonal antibody directed to catalytic domain

Carbonic anhydrase IX (CA IX) is a suitable target for various anticancer strategies. It is a cell surface protein that is present in human tumors, but not in the corresponding normal tissues. Expression of CA IX is induced by hypoxia and correlates with cancer prognosis in many tumor types. Moreover, CA IX is functionally implicated in cancer progression as a pro-survival factor protecting cancer cells against hypoxia and acidosis via its capability to regulate pH and cell adhesion. Cancer-related distribution of CA IX allows for targeting cancer cells by antibodies binding to its extracellular domain, whereas functional involvement of CA IX opens the possibility to hit cancer cells by blocking their adaptation to physiologic stresses via inhibition of CA IX enzyme activity. The latter strategy is recently receiving considerable attention and great efforts are made to produce CA IX-selective inhibitor derivatives with anticancer effects. On the other hand, targeting CA IX-expressing cells by immunotherapy has reached clinical trials and is close to application in treatment of renal cell carcinoma patients. Nevertheless, development and characterization of new CA IX-specific antibodies is still ongoing. Here we describe a mouse monoclonal antibody VII/20 directed to catalytic domain of CA IX. We show that upon binding to CA IX, the VII/20 MAb undergoes efficient receptor-mediated internalization, which is a process regulating abundance and signaling of cell surface proteins and has considerable impact on immunotherapy. We evaluated biological properties of the MAb and demonstrated its capacity to elicit anti-cancer effect in mouse xenograft model of colorectal carcinoma. Thus, the VII/20 MAb might serve as a tool for preclinical studies of immunotherapeutic strategies against non-RCC tumors. These have not been explored so far and include broad spectrum of cancer types, treatment of which might benefit from CA IX-mediated targeting.

The importance of carbonic anhydrase II in red blood cells during exposure of chicken embryos to CO2

The importance of carbonic anhydrase (CA) during exposure of chicken embryos to CO(2) during the second half of incubation was investigated. The protein abundance and activity of CAII in erythrocytes was significantly higher in CO(2)-exposed embryos compared to normal conditions. Daily injections of acetazolamide (ATZ), an inhibitor of CA, increased blood P(CO2) and decreased blood pH in both control and CO(2)-incubated embryos. ATZ increased blood bicarbonate concentration in embryos exposed to normal atmosphere and in day-12 embryos exposed to high CO(2). The tendency of an increased blood potassium concentration in ATZ-injected embryos under standard atmospheric conditions might indicate that protons were exchanged with intracellular potassium. However, there was no evidence for such an exchange in CO(2)-incubated ATZ-treated embryos. This study shows for the first time that chicken embryos adapt to CO(2) during the second half of incubation by increasing CAII protein expression and function in red blood cells. This response may serve to "buffer" elevated CO(2) levels.

Alternative splicing variant of the hypoxia marker carbonic anhydrase IX expressed independently of hypoxia and tumour phenotype

CA IX is a hypoxia-induced, cancer-associated carbonic anhydrase isoform with functional involvement in pH control and cell adhesion. Here we describe an alternative splicing variant of the CA9 mRNA, which does not contain exons 8–9 and is expressed in tumour cells independently of hypoxia. It is also detectable in normal tissues in the absence of the full-length transcript and can therefore produce false-positive data in prognostic studies based on the detection of the hypoxia- and cancer-related CA9 expression. The splicing variant encodes a truncated CA IX protein lacking the C-terminal part of the catalytic domain. It shows diminished catalytic activity and is intracellular or secreted. When overexpressed, it reduces the capacity of the full-length CA IX protein to acidify extracellular pH of hypoxic cells and to bind carbonic anhydrase inhibitor. HeLa cells transfected with the splicing variant cDNA generate spheroids that do not form compact cores, suggesting that they fail to adapt to hypoxic stress. Our data indicate that the splicing variant can functionally interfere with the full-length CA IX. This might be relevant particularly under conditions of mild hypoxia, when the cells do not suffer from severe acidosis and do not need excessive pH control.