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Page 217 Mejia et al. J Transl Genet Genom 2024;8:216-24 https://dx.doi.org/10.20517/jtgg.2024.11

contribute to the bioenergetic defects observed in BTHS lymphoblasts and that enhanced creatine uptake may
serve as one of several compensatory mechanisms for the defective mitochondrial oxidative phosphorylation
observed in these cells.

Keywords: Barth syndrome, TAFFAZIN, protein kinase C delta, B lymphoblasts, mitochondria, cardiolipin, creatine
uptake, monolysocardiolipin

INTRODUCTION
Barth syndrome (BTHS) is a rare X-linked genetic disease caused by a mutation in the TAFAZZIN gene
localized on chromosome Xq28.1 2[1-3] . BTHS is characterized by cardiomyopathy, skeletal myopathy, growth
retardation, neutropenia, and frequently 3-methylglutaconic aciduria. At the cellular level, BTHS patients
exhibit impaired mitochondrial oxidative phosphorylation. The TAFAZZIN gene product is a transacylase
enzyme involved in the remodeling of the mitochondrial phospholipid cardiolipin (CL) from
[4,5]
monolysocardiolipin (MLCL) . Hence, mutations in TAFAZZIN result in reduced CL, elevated MLCL,
and impairment in oxidative phosphorylation [1-3,6] . In several studies, Epstein-Barr virus transformed
lymphoblasts from patients have been used to examine BTHS metabolic pathology .
[6-9]

Protein kinase C delta (PKCδ) is a signaling kinase that regulates many cellular responses and is controlled
via multi-site phosphorylation [10-13] . The PKCδ pathway adjusts the fuel flux from glycolytic sources to the
intensity of mitochondrial respiration, thus controlling mitochondrial oxidative phosphorylation. In
mitochondria, the PKCδ signalosome exists in a high molecular weight complex, which includes
cytochrome c as the upstream driver of PKCδ, the adapter protein p66Shc as the assembly platform, and
retinol [12,14] . All four components are required for activation of PKCδ signaling in mitochondria. We
previously demonstrated that PKCδ phosphorylation was altered on several sites in BTHS patient B
[15]
lymphoblasts compared to control patient B lymphoblasts . Given that PKCδ is involved in B lymphocyte
differentiation and cell fate and that altered phosphorylation of PKCδ may impact its activation, it is
[16]
possible that PKCδ associated with a higher molecular weight complex is altered in mitochondria of BTHS B
lymphoblasts.

Creatine is an amino acid derivative that, upon entrance into cells, is phosphorylated to phosphocreatine
and used as an energy buffer. For example, during increased energy demand, ATP is rapidly resynthesized
from ADP and phosphocreatine. Thus, creatine uptake is required to support phosphocreatine generation.
Since oxidative phosphorylation is impaired in BTHS B lymphoblasts, it is possible that enhanced creatine
uptake may occur as a compensatory mechanism to maintain energy metabolism, as observed with other
[17]
metabolites such as glucose .

In this study, we demonstrate for the first time that PKCδ is associated with a higher molecular weight
complex in B lymphoblast mitochondria but that its association with this higher molecular weight complex
is reduced in BTHS patient B lymphoblasts mitochondria compared to age-matched controls in spite of an
increase in overall PKCδ protein expression. We hypothesize that the lack of PKCδ within this high
molecular weight complex may contribute to defective mitochondrial PKCδ signaling and thus to the
bioenergetic defects observed in BTHS cells. Moreover, we observe enhanced creatine uptake into BTHS
patient B lymphoblasts compared to control cells. We hypothesize that enhanced creatine uptake may, in
part, contribute as a compensatory mechanism to maintain energy metabolism in BTHS B lymphoblasts.