The number of mitochondrial DNA mutations as a genetic feature for hair cycle arrest (alopecia X) in Pomeranian dogs

Evaluation of phenotypic risk indicators for the development of alopecia X (hair cycle arrest) in Pomeranian dogs in the Netherlands and Belgium

BACKGROUND

Alopecia X (AX) is a common noninflammatory alopecic condition of Pomeranian dogs with an unknown cause. While a genetic aetiology is suspected, no current tests can predict the development of this disorder or confirm the aetiology. Therefore, identifying potential risk indicators for the development of AX would be of value in this breed.

OBJECTIVES

This study aimed to identify risk indicators for AX in Pomeranians in the Netherlands and Belgium.

MATERIALS AND METHODS

A retrospective epidemiological study was conducted in the Netherlands and the Dutch-speaking parts of Belgium between March 2022 and August 2023, using an online survey of Pomeranian owners. Variables such as sex, birth season, neutering status, coat type, coat colour, grooming frequency and whether the dog experienced an 'ugly stage' of hair coat growth or not were recorded, along with the presence or absence of alopecia and the age of onset of the condition.

RESULTS

Of 234 completed surveys, 211 were eligible for analysis. Statistical analysis with a Cox proportional-hazard model indicated that the risk of developing alopecia was greater for a woolly versus shiny coat and for males versus females.

CONCLUSIONS AND CLINICAL RELEVANCE

A woolly hair coat type and male sex were identified as risk indicators for developing AX in Pomeranian dogs in this study.

Hair fragility (trichorrhexis nodosa) in alopecic Pomeranian dogs

BACKGROUND

While alopecia associated with hair cycle arrest (HCA, Alopecia X) is well-recognised in Pomeranian dogs, the authors are unaware of reports of concurrent hair fragility.

HYPOTHESIS/OBJECTIVES

Following the observation of frequent hair shaft abnormalities in alopecic Pomeranians, we hypothesised that hair fragility events would be more frequent in dogs with a phenotype of HCA when compared to dogs with normal coats.

ANIMALS

Eight alopecic Pomeranian dogs or crosses with a phenotype of HCA and 36 unaffected Pomeranians with owner-reported normal hair coats.

MATERIALS AND METHODS

All affected dogs underwent dermatological examination and clinicopathological evaluations. Hair samples, plucked from affected areas or obtained by brushing from unaffected dogs, were examined microscopically for structural abnormalities. Hair fragility events were characterised as trichorrhexis nodosa (TN) or longitudinal splits and were expressed per 10 mg of hair. A reference interval was calculated from the number of hair fragility events in the samples from unaffected dogs.

RESULTS

The upper reference limit (with 90% confidence) from samples of 35 unaffected Pomeranians (one outlier excluded) was 9.75 hair fragility events per 10 mg of hair. The median (range) of fragility events in eight dogs with a phenotype of HCA was 66.0 (30.2-166.7) per 10 mg of hair.

CONCLUSIONS AND CLINICAL RELEVANCE

Clinicians should routinely perform trichography in Pomeranians with HCA because abundant hair abnormalities, particularly TN, may contribute to poor hair coat quality. Further studies are required to establish the pathophysiology of and treatments for these fragility events and to determine their predictive value for HCA.

Autophagy Dysfunction: The Kernel of Hair Loss?

Autophagy is recognized as a crucial regulatory process, instrumental in the removal of senescent, dysfunctional, and damaged cells. Within the autophagic process, lysosomal digestion plays a critical role in the elimination of impaired organelles, thus preserving fundamental cellular metabolic functions and various biological processes. Mitophagy, a targeted autophagic process that specifically focuses on mitochondria, is essential for sustaining cellular health and energy balance. Therefore, a deep comprehension of the operational mechanisms and implications of autophagy and mitophagy is vital for disease prevention and treatment. In this context, we examine the role of autophagy and mitophagy during hair follicle cycles, closely scrutinizing their potential association with hair loss. We also conduct a thorough review of the regulatory mechanisms behind autophagy and mitophagy, highlighting their interaction with hair follicle stem cells and dermal papilla cells. In conclusion, we investigate the potential of manipulating autophagy and mitophagy pathways to develop innovative therapeutic strategies for hair loss.

Dermoscopic findings and comparison of usefulness of longitudinal versus transversal sections in the histological diagnosis of alopecia X

BACKGROUND

A combination of dermoscopic and histological findings may provide useful information for the diagnosis of hair follicle diseases. However, there are no studies on dermoscopic-histopathological correlations in dogs affected by alopecia X, and comparison of longitudinal versus transversal sectioning of skin biopsy specimens in the assessment of this hair loss disorder has not been thoroughly investigated.

HYPOTHESIS/OBJECTIVES

The aim of this study was to correlate dermoscopic and histological features using both longitudinal and transversal sectioning of skin biopsy samples to gain additional information for the diagnosis of alopecia X.

ANIMALS

Nineteen Pomeranian dogs affected by alopecia X and five healthy Pomeranians as controls.

MATERIALS AND METHODS

Dermoscopic-histological correlation was performed within the diseased group, whereas histological comparisons against controls. The demographic and clinical characteristics also were related to the histological findings.

RESULTS

The dermoscopic findings revealed scattered, thinned, short hairs mixed with amorphous keratoseborrhoeic-like material (follicular plugging), perifollicular and intrafollicular scaling, and hyperpigmentation varying from pinpoint black spots to a diffuse texture. Dermoscopic findings correlated with histological findings for selected qualitative and quantitative findings. The usefulness of transversal sections was demonstrated in accurately determining the hair follicular density and counts, growth arrest phases and in identifying mineralisation of hair follicle basement membrane when compared to the longitudinal. Conversely, no correlations between histological findings and demographic and clinical characteristics were detected.

CONCLUSIONS AND CLINICAL RELEVANCE

These data provide evidence of the usefulness of dermoscopic evaluation as an accessory diagnostic tool and of transversal sections of skin biopsies as complementary to the diagnosis of alopecia X.

Alopecia X in a cloned Pomeranian dog

A two-year-old Pomeranian dog with Alopecia X was cloned after accidental death. Despite earlier castration, the cloned animal developed the same lesions of Alopecia X at the same age. This observation suggests that the disease is due to genetically programmed hair cycle arrest without strong environmental influences.

Optimal microneedle length for hair regrowth in hair cycle arrest (alopecia X) in six dogs

BACKGROUND

Hair cycle arrest (HCA) is a chronic alopecic disorder in dogs. Clinical responses vary and are often insufficient. Microneedling (MN) has been used as a successful treatment for HCA in dogs; ideal protocols have not yet been established.

OBJECTIVES

The objective of the study was to compare the efficacy and safety of three needle lengths for MN in dogs with HCA.

ANIMALS

Six unrelated client-owned dogs, including five Pomeranians and one mixed-breed dog, diagnosed with HCA.

MATERIALS AND METHODS

Individual alopecic sites were divided into three sections. For each section, different lengths of needles (1, 2 and 3 mm) were used. Efficacy and safety were evaluated at 1, 3 and 6 months. Treated sections were monitored for 20 months.

RESULTS

Three months after treatment with 3 mm needles, all sections showed hair regrowth. There was no hair regrowth in two of six sections treated with 2 mm needles, and four of six sections did not show a response to treatment with 1 mm needles. Two dogs developed transient pruritus. Five of six dogs had recurrent hair loss between 5 and 16 months of follow-up.

CONCLUSION AND CLINICAL RELEVANCE

Microneedling using longer needles stimulated better hair regrowth in dogs with HCA. Alopecia relapsed in most dogs and minor pruritus occurred in some dogs.

Canine noninflammatory alopecia: An approach to its classification and a diagnostic aid

Noninflammatory alopecia is common in dogs and is a frequent cause to consult a veterinarian. It is also a common reason to take biopsies. Noninflammatory alopecia can be attributed to a decreased formation or cytodifferentiation of the hair follicle or the hair shaft in utero, resulting in congenital alopecia. Congenital alopecia often has a hereditary cause, and examples of such disorders are ectodermal dysplasias associated with gene variants of the ectodysplasin A gene. Noninflammatory alopecia may also be caused by impaired postnatal regeneration of hair follicles or shafts. Such disorders may have a clear breed predilection, and alopecia starts early in life. A hereditary background is suspected in those cases but has not been proven. They are referred to as follicular dysplasia although some of these disorders present histologically like a hair cycle disturbance. Late-onset alopecia is usually acquired and may be associated with endocrinopathies. Other possible causes are impaired vascular perfusion or stress. As the hair follicle has limited possible responses to altered regulation, and histopathology may change during the course of a disease, a detailed clinical history, thorough clinical examination including blood work, appropriate biopsy site selection, and detailed histological findings need to be combined to achieve a final diagnosis. This review aims to provide an overview about the known noninflammatory alopecic disorders in dogs. As the pathogenesis of most disorders is unknown, some statements are based on comparative aspects or reflect the authors' opinion.

Cold atmospheric microwave plasma (CAMP) stimulates dermal papilla cell proliferation by inducing β-catenin signaling

Hair loss or alopecia is an unpleasant symptom that exacerbates an individual's self-esteem and requires appropriate treatment. The Wnt/β-catenin signaling is a central pathway that promotes dermal papilla induction and keratinocyte proliferation during hair follicle renewal. GSK-3β inactivated by its upstream Akt and ubiquitin-specific protease 47 (USP47) has been shown to inhibit β-catenin degradation. The cold atmospheric microwave plasma (CAMP) is microwave energy enriched with mixtures of radicals. CAMP has been reported to have antibacterial and antifungal activities with wound healing activity against skin infection; however, the effect of CAMP on hair loss treatment has not been reported. We aimed to investigate the effect of CAMP on promoting hair renewal in vitro and to elucidate the molecular mechanism, targeting β-catenin signaling and YAP/TAZ, the co-activators in the Hippo pathway, in human dermal papilla cells (hDPCs). We also evaluated plasma effects on the interaction between hDPCs and HaCaT keratinocytes. The hDPCs were treated with plasma-activating media (PAM) or gas-activating media (GAM). The biological outcomes were determined by MTT assay, qRT-PCR, western blot analysis, immunoprecipitation, and immunofluorescence. We found that β-catenin signaling and YAP/TAZ were significantly increased in PAM-treated hDPCs. PAM treatment also induced β-catenin translocation and inhibited β-catenin ubiquitination by activating Akt/GSK-3β signaling and upregulating USP47 expression. In addition, hDPCs were more aggregated with keratinocytes in PAM-treated cells compared with control. HaCaT cells cultured in a conditioned medium derived from PAM-treated hDPCs exhibited an enhancing effect on activating YAP/TAZ and β-catenin signaling. These findings suggested that CAMP may be a new therapeutic alternative for alopecic treatment.