Inhibition of pyruvate oxidation as a versatile stimulator of the hair cycle in models of alopecia

Activation of mitochondrial aldehyde dehydrogenase 2 promotes hair growth in human hair follicles

INTRODUCTION

Hair loss is a common phenomenon associated with various environmental and genetic factors. Mitochondrial dysfunction-induced oxidative stress has been recognized as a crucial determinant of hair follicle (HF) biology. Aldehyde dehydrogenase 2 (ALDH2) mitigates oxidative stress by detoxifying acetaldehyde. This study investigated the potential role of ALDH2 modulation in HF function and hair growth promotion.

OBJECTIVES

To evaluate the effects of ALDH2 activation on oxidative stress in HFs and hair growth promotion.

METHODS

The modulatory role of ALDH2 on HFs was investigated using an ALDH2 activator. ALDH2 expression in human HFs was evaluated through in vitro immunofluorescence staining. Ex vivo HF organ culture was employed to assess hair shaft elongation, while the fluorescence probe 2',7'- dichlorodihydrofluorescein diacetate was utilized to detect reactive oxygen species (ROS). An in vivo mouse model was used to determine whether ALDH2 activation induces anagen.

RESULTS

During the anagen phase, ALDH2 showed significantly higher intensity than that in the telogen phase, and its expression was primarily localized along the outer layer of HFs. ALDH2 activation promoted anagen phase induction by reducing ROS levels and enhancing reactive aldehyde clearance, which indicated that ALDH2 functions as a ROS scavenger within HFs. Moreover, ALDH2 activation upregulated Akt/GSK 3β/β-catenin signaling in HFs.

CONCLUSIONS

Our findings highlight the hair growth promotion effects of ALDH2 activation in HFs and its potential as a promising therapeutic approach for promoting anagen induction.

iTRAQ-based quantitative proteomics revealing the therapeutic mechanism of a medicinal and edible formula YH0618 in reducing doxorubicin-induced alopecia by targeting keratins and TGF-β/Smad3 pathway

YH0618, a medicinal and edible formulation, has demonstrated the potential to alleviate doxorubicin-induced alopecia in animal studies and clinical trials. However, the mechanisms underlying its therapeutic effects remain unexplored. The objective of this study was to ascertain possible therapeutic targets of YH0618 in the treatment of doxorubicin-induced alopecia. The assessment of hair loss was conducted through the measurement of the proportion of the affected area and the examination of skin histology. Isobaric tags for relative and absolute quantification (iTRAQ) in quantitative proteomics was employed to discern proteins that exhibited variable expressions. The major proteins associated with doxorubicin-induced alopecia were identified using gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The interaction network of the differentially expressed proteins was constructed using the STRING database and the Python software. The study analyzed a total of 3894 proteins extracted from the skin tissue of mice. Doxorubicin treatment resulted in the upregulation of 18 distinct proteins, whereas one differential protein was found to be downregulated. The above effects were reinstated after the administration of the YH0618 therapy. The bioinformatic study revealed that the identified proteins exhibited enrichment in many biological processes, including staphylococcus aureus infection, estrogen signaling route, pyruvate metabolism, chemical carcinogenesis, and PPAR signaling pathway. The results of Western blot revealed that the levels of keratin 81 (Krt81), keratin 34 (Krt34), keratin 33a (Krt33a), and Sma and MAD-related protein 3 (Smad3) were upregulated in response to doxorubicin treatment, and were attenuated by the administration of YH0618. These four proteins are likely to correlate with DOX-induced alopecia and serve as promising therapeutic targets for YH0618. This work presents significant insights and empirical evidence for comprehending the process underlying chemotherapy-induced alopecia, paving the way for exploring innovative therapeutic or preventive strategies employing herbal items.

Fifty years of the mitochondrial pyruvate carrier: New insights into its structure, function, and inhibition

The mitochondrial pyruvate carrier (MPC) resides in the mitochondrial inner membrane, where it links cytosolic and mitochondrial metabolism by transporting pyruvate produced in glycolysis into the mitochondrial matrix. Due to its central metabolic role, it has been proposed as a potential drug target for diabetes, non-alcoholic fatty liver disease, neurodegeneration, and cancers relying on mitochondrial metabolism. Little is known about the structure and mechanism of MPC, as the proteins involved were only identified a decade ago and technical difficulties concerning their purification and stability have hindered progress in functional and structural analyses. The functional unit of MPC is a hetero-dimer comprising two small homologous membrane proteins, MPC1/MPC2 in humans, with the alternative complex MPC1L/MPC2 forming in the testis, but MPC proteins are found throughout the tree of life. The predicted topology of each protomer consists of an amphipathic helix followed by three transmembrane helices. An increasing number of inhibitors are being identified, expanding MPC pharmacology and providing insights into the inhibitory mechanism. Here, we provide critical insights on the composition, structure, and function of the complex and we summarize the different classes of small molecule inhibitors and their potential in therapeutics.

Dysregulated behaviour of hair follicle stem cells triggers alopecia and provides potential therapeutic targets

Due to a steady increase in the number of individuals suffering from alopecia, this condition has recently received increasing attention. Alopecia can be caused by various pathological, environmental or psychological factors, eventually resulting in abnormalities in hair follicle (HF) structures or HF regeneration disorders, especially dysregulated hair follicle stem cell (HFSC) behaviour. HFSC behaviour includes activation, proliferation and differentiation. Appropriate HFSC behaviour sustains a persistent hair cycle (HC). HFSC behaviour is mainly influenced by HFSC metabolism, ageing, and the microenvironment. In this review, we summarize recent findings on how HFSC metabolism, ageing and the microenvironment give rise to hair growth disorders, as well as related genes and signalling pathways. Recent research on the application of stem cell-based hair tissue engineering and regenerative medicine to treat alopecia is also summarized. Determining how dysregulated HFSC behaviour underlies alopecia would be helpful in identifying potential therapeutic targets.

Mitochondrial pyruvate carrier inhibitors improve metabolic parameters in diet-induced obese mice

The mitochondrial pyruvate carrier (MPC) is an inner mitochondrial membrane complex that plays a critical role in intermediary metabolism. Inhibition of the MPC, especially in liver, may have efficacy for treating type 2 diabetes mellitus. Herein, we examined the antidiabetic effects of zaprinast and 7ACC2, small molecules which have been reported to act as MPC inhibitors. Both compounds activated a bioluminescence resonance energy transfer–based MPC reporter assay (reporter sensitive to pyruvate) and potently inhibited pyruvate-mediated respiration in isolated mitochondria. Furthermore, zaprinast and 7ACC2 acutely improved glucose tolerance in diet-induced obese mice in vivo. Although some findings were suggestive of improved insulin sensitivity, hyperinsulinemic–euglycemic clamp studies did not detect enhanced insulin action in response to 7ACC2 treatment. Rather, our data suggest acute glucose-lowering effects of MPC inhibition may be due to suppressed hepatic gluconeogenesis. Finally, we used reporter sensitive to pyruvate to screen a chemical library of drugs and identified 35 potentially novel MPC modulators. Using available evidence, we generated a pharmacophore model to prioritize which hits to pursue. Our analysis revealed carsalam and six quinolone antibiotics, as well as 7ACC1, share a common pharmacophore with 7ACC2. We validated that these compounds are novel inhibitors of the MPC and suppress hepatocyte glucose production and demonstrated that one quinolone (nalidixic acid) improved glucose tolerance in obese mice. In conclusion, these data demonstrate the feasibility of therapeutic targeting of the MPC for treating diabetes and provide scaffolds that can be used to develop potent and novel classes of MPC inhibitors.