Thiamine Deficiency Increases Ca2+ Current and CaV1.2 L-type Ca2+ Channel Levels in Cerebellum Granular Neurons

Association between thiamine intake and depression: A national cross-sectional study

BACKGROUND

Recent years have seen increasing attention to improving depressive symptoms through dietary intakes, yet the association between thiamine intake and depression remains unclear. The present study aimed to explore this association using data from an American cross-sectional study.

METHODS

We explored the association of covariates, exposure, and outcome with logistic regression equations. Multivariable regression models were performed to further exclude confounding factors. To investigate nonlinear relationships, we employed restricted cubic splines. Recursive algorithms were utilized to identify inflection points. Additionally, we conducted stratified analyses by age and sex to uncover differences among subgroups.

RESULTS

When all covariates were adjusted, the association between thiamine intake and depression was not statistically significant [0.93 (0.82, 1.07)]. In the linear trend test using Q1 as the reference, the ORs (95%CI) for Q2, Q3, and Q4 were 0.87 (0.73, 1.04), 0.83 (0.68, 1.00), and 0.92 (0.73, 1.16), which suggested that the association might be nonlinear. We then confirmed this nonlinear relationship with a restricted cubic spline, and the inflection point of 1.35 mg/day was calculated. Before the inflection point, the effect value of the relationship was 0.68 (0.53, 0.89). After the inflection point, no significant association was found [1.10 (0.92, 1.31)]. Stratified analyses revealed that this nonlinear relationship was consistent among women and individuals aged <60 years.

DISCUSSION

In this cross-sectional study among American general adults, we found a nonlinear association between thiamine intake and depression and further observed differences by age and sex.

Plasma membrane calcium ATPase powered by glycolysis is the main mechanism for calcium clearance in the hippocampal pyramidal neuron

AIMS

This study sought to elucidate the primary ATP-dependent mechanisms involved in clearing cytosolic Ca2+ in neurons and determine the predominant ATP-generating pathway-glycolysis or tricarboxylic acid cycle/oxidative phosphorylation (TCA/OxPhos)-associated with these mechanisms in hippocampal pyramidal neurons.

MAIN METHODS

Our investigation involved evaluating basal Ca2+ levels and analyzing the kinetic characteristics of evoked neuronal Ca2+ transients after selectively combined the inhibition/blockade of key ATP-dependent mechanisms with the suppression of either TCA/OxPhos or glycolytic ATP sources.

KEY FINDINGS

Our findings unveiled that the plasma membrane Ca2+ ATPase (PMCA) serves as the principal ATP-dependent mechanism for clearance cytosolic Ca2+ in hippocampal pyramidal neurons, both during rest and neuronal activity. Remarkably, during cellular activity, PMCA relies on ATP derived from glycolysis, challenging the traditional notion of neuronal reliance on TCA/OxPhos for ATP. Other mechanisms for Ca2+ clearance in pyramidal neurons, such as SERCA and NCX, appear to be dependent on TCA/OxPhos. Interestingly, at rest, the ATP required to fuel PMCA and SERCA, the two main mechanisms to keep resting Ca2+, seems to originate from a source other than glycolysis or the TCA/OxPhos.

SIGNIFICANCE

These findings underscore the vital role of glycolysis in bolstering PMCA neuronal function to uphold Ca2+ homeostasis. Moreover, they elucidate the varying dependencies of cytoplasmic Ca2+ clearance mechanisms on distinct energy sources for their operation.

Protection of Cholinergic Neurons against Zinc Toxicity by Glial Cells in Thiamine-Deficient Media

Brain pathologies evoked by thiamine deficiency can be aggravated by mild zinc excess. Cholinergic neurons are the most susceptible to such cytotoxic signals. Sub-toxic zinc excess aggravates the injury of neuronal SN56 cholinergic cells under mild thiamine deficiency. The excessive cell loss is caused by Zn interference with acetyl-CoA metabolism. The aim of this work was to investigate whether and how astroglial C6 cells alleviated the neurotoxicity of Zn to cultured SN56 cells in thiamine-deficient media. Low Zn concentrations did not affect astroglial C6 and primary glial cell viability in thiamine-deficient conditions. Additionally, parameters of energy metabolism were not significantly changed. Amprolium (a competitive inhibitor of thiamine uptake) augmented thiamine pyrophosphate deficits in cells, while co-treatment with Zn enhanced the toxic effect on acetyl-CoA metabolism. SN56 cholinergic neuronal cells were more susceptible to these combined insults than C6 and primary glial cells, which affected pyruvate dehydrogenase activity and the acetyl-CoA level. A co-culture of SN56 neurons with astroglial cells in thiamine-deficient medium eliminated Zn-evoked neuronal loss. These data indicate that astroglial cells protect neurons against Zn and thiamine deficiency neurotoxicity by preserving the acetyl-CoA level.

Thiamine Deficiency Increases Intrinsic Excitability of Mouse Cerebellar Purkinje Cells

Thiamine deficiency is associated with cerebellar dysfunction; however, the consequences of thiamine deficiency on the electrophysiological properties of cerebellar Purkinje cells are poorly understood. Here, we evaluated these parameters in brain slices containing cerebellar vermis. Adult mice were maintained for 12-13 days on a thiamine-free diet coupled with daily injections of pyrithiamine, an inhibitor of thiamine phosphorylation. Morphological analysis revealed a 20% reduction in Purkinje cell and nuclear volume in thiamine-deficient animals compared to feeding-matched controls, with no reduction in cell count. Under whole-cell current clamp, thiamine-deficient Purkinje cells required significantly less current injection to fire an action potential. This reduction in rheobase was not due to a change in voltage threshold. Rather, thiamine-deficient neurons presented significantly higher input resistance specifically in the voltage range just below threshold, which increases their sensitivity to current at these critical membrane potentials. In addition, thiamine deficiency caused a significant decrease in the amplitude of the action potential afterhyperpolarization, broadened the action potential, and decreased the current threshold for depolarization block. When thiamine-deficient animals were allowed to recover for 1 week on a normal diet, rheobase, threshold, action potential half-width, and depolarization block threshold were no longer different from controls. We conclude that thiamine deficiency causes significant but reversible changes to the electrophysiology properties of Purkinje cells prior to pathological morphological alterations or cell loss. Thus, the data obtained in the present study indicate that increased excitability of Purkinje cells may represent a leading indicator of cerebellar dysfunction caused by lack of thiamine.

Developmental Aspects of Glucose and Calcium Availability on the Persistence of Memory Function Over the Lifespan

An important aspect concerning the underlying nature of memory function is an understanding of how memories are acquired and lost. The stability, and ultimate demise, of memory over the lifespan of an organism remains a critical topic in determining the neurobiological mechanisms that mediate memory representations. This has important implications for the elucidation and treatment of neurodegenerative diseases such as Alzheimer's disease (AD). One important question in the context of preserving functional plasticity over the lifespan is the determination of the neurobiological structural and functional changes that contribute to the formation of memory during the juvenile time frame that might provide protection against later memory dysfunction by promoting the establishment of redundant neural pathways. The main question being, if memory formation during the juvenile period does strengthen and preserve memory stability over the lifespan, what are the neurobiological structural or functional substrates that mediate this effect? One neural attribute whose function may be altered with early life experience and provide a mechanism to preserve memory through the lifespan is glucose transport-linked calcium (Ca2+) buffering. Because peak increases in glucose utilization overlap with a timeframe during which spatial training can enhance later memory processing, it might be the case that learning-associated changes in glucose utilization would provide an important neural functional change to preserve memory function throughout the lifespan. The glucose transporters are proteins that are reduced in AD pathology and there is evidence that glucose reductions can impair Ca2+ buffering. In the absence of an appropriate supply of ATP, provided via glucose transport and glycolysis, Ca2+ levels can rise leading to neural vulnerability with ensuing pathological outcomes. In this review, we explore the hypothesis that enhancing glucose utilization with spatial training during the preadolescent period will provide a functional enhancement that regulates glucose-dependent Ca2+ signaling during aging or neurodegeneration and provide essential neural resources to preserve functional plasticity and memory function.

Altered Sodium and Potassium, but not Calcium Currents in Cerebellar Granule Cells in an In Vitro Model of Neuronal Injury

Acute injury of central nervous system (CNS) starts a cascade of morphological, molecular, and functional changes including formation of a fibrotic scar, expression of transforming growth factor beta 1 (TGF-β1), and expression of extracellular matrix proteins leading to arrested neurite outgrowth and failed regeneration. We assessed alteration of electrophysiological properties of cerebellar granule cells (CGCs) in two in vitro models of neuronal injury: (i) model of fibrotic scar created from coculture of meningeal fibroblasts and cerebral astrocytes with addition of TGF-β1; (ii) a simplified model based on administration of TGF-β1 to CGCs culture. Both models reproduced suppression of neurite outgrowth caused by neuronal injury, which was equally restored by chondroitinase ABC (ChABC), a key disruptor of fibrotic scar formation. Voltage-dependent calcium current was not affected in either injury model. However, intracellular calcium concentration could be altered as an expression of inositol trisphosphate receptor type 1 was suppressed by TGF-β1 and restored by ChABC. Voltage-dependent sodium current was significantly suppressed in CGCs cultured on a model of fibrotic scar and was only partly restored by ChABC. Administration of TGF-β1 significantly shifted current-voltage relation of sodium current toward more positive membrane potential without change to maximal current amplitude. Both transient and sustained potassium currents were significantly suppressed on a fibrotic scar and restored by ChABC to their control amplitudes. In contrast, TGF-β1 itself significantly upregulated transient and did not change sustained potassium current. Observed changes of voltage-dependent ion currents may contribute to known morphological and functional changes in injured CNS.