Expression of 25 kDa thiamine triphosphatase in rodent tissues using quantitative PCR and characterization of its mRNA

Update on Thiamine Triphosphorylated Derivatives and Metabolizing Enzymatic Complexes

While the cellular functions of the coenzyme thiamine (vitamin B1) diphosphate (ThDP) are well characterized, the triphosphorylated thiamine derivatives, thiamine triphosphate (ThTP) and adenosine thiamine triphosphate (AThTP), still represent an intriguing mystery. They are present, generally in small amounts, in nearly all organisms, bacteria, fungi, plants, and animals. The synthesis of ThTP seems to require ATP synthase by a mechanism similar to ATP synthesis. In E. coli, ThTP is synthesized during amino acid starvation, while in plants, its synthesis is dependent on photosynthetic processes. In E. coli, ThTP synthesis probably requires oxidation of pyruvate and may play a role at the interface between energy and amino acid metabolism. In animal cells, no mechanism of regulation is known. Cytosolic ThTP levels are controlled by a highly specific cytosolic thiamine triphosphatase (ThTPase), coded by thtpa, and belonging to the ubiquitous family of the triphosphate tunnel metalloenzymes (TTMs). While members of this protein family are found in nearly all living organisms, where they bind organic and inorganic triphosphates, ThTPase activity seems to be restricted to animals. In mammals, THTPA is ubiquitously expressed with probable post-transcriptional regulation. Much less is known about the recently discovered AThTP. In E. coli, AThTP is synthesized by a high molecular weight protein complex from ThDP and ATP or ADP in response to energy stress. A better understanding of these two thiamine derivatives will require the use of transgenic models.

Thiamine triphosphate: a ubiquitous molecule in search of a physiological role

Thiamine triphosphate (ThTP) was discovered over 60 years ago and it was long thought to be a specifically neuroactive compound. Its presence in most cell types, from bacteria to mammals, would suggest a more general role but this remains undefined. In contrast to thiamine diphosphate (ThDP), ThTP is not a coenzyme. In E. coli cells, ThTP is transiently produced in response to amino acid starvation, while in mammalian cells, it is constitutively produced at a low rate. Though it was long thought that ThTP was synthesized by a ThDP:ATP phosphotransferase, more recent studies indicate that it can be synthesized by two different enzymes: (1) adenylate kinase 1 in the cytosol and (2) FoF1-ATP synthase in brain mitochondria. Both mechanisms are conserved from bacteria to mammals. Thus ThTP synthesis does not seem to require a specific enzyme. In contrast, its hydrolysis is catalyzed, at least in mammalian tissues, by a very specific cytosolic thiamine triphosphatase (ThTPase), controlling the steady-state cellular concentration of ThTP. In some tissues where adenylate kinase activity is high and ThTPase is absent, ThTP accumulates, reaching ≥ 70% of total thiamine, with no obvious physiological consequences. In some animal tissues, ThTP was able to phosphorylate proteins, and activate a high-conductance anion channel in vitro. These observations raise the possibility that ThTP is part of a still uncharacterized cellular signaling pathway. On the other hand, its synthesis by a chemiosmotic mechanism in mitochondria and respiring bacteria might suggest a role in cellular energetics.

Paradoxical effects of alcohol and thiamine deficiency on the eye opening in rat pups

OBJECTIVE

The present study attempts to determine whether developmental thiamine (B1 vitamin) deficiency and developmental ethanol exposure disturb eye opening in Wistar rat pups.

METHODS

During gestation and lactation, Wistar rat dams were exposed to the following treatments: (1) Prenatal thiamine-deficient dams; (2) perinatal thiamine-deficient dams; (3) postnatal thiamine-deficient dams; (4) 12% alcohol/water drinking mothers; (5) mothers drinking 12% alcohol/water + thiamine hydrochloride mixture; (6) ad libitum control dams. Pair-feeding treatments controlled malnutrition related to thiamine deficiency: (7) Prenatal pair-fed dams; (8) perinatal pair-fed dams; (9) postnatal pair-fed dams and included also the control of alcohol consummation: (10) pair-fed saccharose dams. After birth, from postnatal day 10 (P10) to P18, eye opening was observed in the pups bred by ten different experimental dams.

RESULTS

The present experiments showed eye opening to be delayed strongly in perinatal thiamine-deficient pups only. Consequently, our study suggests perinatal thiamine deficiency to interfere with photoreceptors differentiation in the rat retina. In addition, our results reveal that developmental alcohol exposure-induced premature eye opening contrasted paradoxically with perinatal thiamine deficiency-induced delayed opening.

CONCLUSIONS

The results suggest differential actions of alcohol and thiamine deficiency on cellular genesis in the rat retina.

Comparative effects of alcohol and thiamine deficiency on the developing central nervous system

The present study addresses the still unresolved issue of the character of alcohol-thiamine metabolic interferences in the developing central nervous system (CNS). Investigations compare developmental neurotoxicity evoked by three patterns of maternal thiamine deficiency (pre, peri and postnatal), with two patterns of maternal chronic alcohol intake (alcohol alone and alcohol+thiamine cotreatment), on seven neurodevelopmental abilities in the offspring. The three patterns of thiamine deficiency, pair-compared with controls, highlight four sequences of development: (1) embryonic-perinatal sequence; (2) perinatal-postnatal sequence; (3) "ontogeny in ontogeny out" sequence; (4) "off and on" developing sequence. The results suggest a temporally- and regionally emergence of structures and centers underlying functional maturation during CNS ontogenesis. Furthermore, both developmental thiamine deficiencies and ethanol exposure produce two waves of neurofunctional alterations, peaking at P15 (postnatal day 15) and P25, respectively. The first peak of vulnerability is a prenatal event; it may interfere with the periods of intense cellular proliferation and migration. The second peak represents both perinatal and postnatal events; it may interfere with the periods of cellular differentiation, synaptogenesis, axonogenesis and myelinogenesis. Alcohol+thiamine cotreatment fails to reduce the first peak, but neutralizes essentially the second peak. The results suggest that alcohol interferes with thiamine during cellular differentiation and membrane developmental processes mainly. Indeed, among the three conditions of thiamine-deficient diet, only perinatal thiamine deficiency exhibits a closer relationship with developmental alcohol exposure. Together, these observations suggest that the critical period for alcohol-thiamine antagonism occurs perinatally and affects primarily cellular differentiation.

Thiamine status in humans and content of phosphorylated thiamine derivatives in biopsies and cultured cells

Background

Thiamine (vitamin B1) is an essential molecule for all life forms because thiamine diphosphate (ThDP) is an indispensable cofactor for oxidative energy metabolism. The less abundant thiamine monophosphate (ThMP), thiamine triphosphate (ThTP) and adenosine thiamine triphosphate (AThTP), present in many organisms, may have still unidentified physiological functions. Diseases linked to thiamine deficiency (polyneuritis, Wernicke-Korsakoff syndrome) remain frequent among alcohol abusers and other risk populations. This is the first comprehensive study on the distribution of thiamine derivatives in human biopsies, body fluids and cell lines.

Methodology and Principal Findings

Thiamine derivatives were determined by HPLC. In human tissues, the total thiamine content is lower than in other animal species. ThDP is the major thiamine compound and tissue levels decrease at high age. In semen, ThDP content correlates with the concentration of spermatozoa but not with their motility. The proportion of ThTP is higher in humans than in rodents, probably because of a lower 25-kDa ThTPase activity. The expression and activity of this enzyme seems to correlate with the degree of cell differentiation. ThTP was present in nearly all brain and muscle samples and in ∼60% of other tissue samples, in particular fetal tissue and cultured cells. A low ([ThTP]+[ThMP])/([Thiamine]+[ThMP]) ratio was found in cardiovascular tissues of patients with cardiac insufficiency. AThTP was detected only sporadically in adult tissues but was found more consistently in fetal tissues and cell lines.

Conclusions and Significance

The high sensitivity of humans to thiamine deficiency is probably linked to low circulating thiamine concentrations and low ThDP tissue contents. ThTP levels are relatively high in many human tissues, as a result of low expression of the 25-kDa ThTPase. Another novel finding is the presence of ThTP and AThTP in poorly differentiated fast-growing cells, suggesting a hitherto unsuspected link between these compounds and cell division or differentiation.