Decreased Hypothalamic Prohormone Convertase Expression in Huntington Disease Patients

Whole Genome Resequencing Reveals Selection Signals Related to Wool Color in Sheep

Wool color is controlled by a variety of genes. Although the gene regulation of some wool colors has been studied in relative depth, there may still be unknown genetic variants and control genes for some colors or different breeds of wool that need to be identified and recognized by whole genome resequencing. Therefore, we used whole genome resequencing data to compare and analyze sheep populations of different breeds by population differentiation index and nucleotide diversity ratios (Fst and θπ ratio) as well as extended haplotype purity between populations (XP-EHH) to reveal selection signals related to wool coloration in sheep. Screening in the non-white wool color group (G1 vs. G2) yielded 365 candidate genes, among which PDE4B, GMDS, GATA1, RCOR1, MAPK4, SLC36A1, and PPP3CA were associated with the formation of non-white wool; an enrichment analysis of the candidate genes yielded 21 significant GO terms and 49 significant KEGG pathways (p < 0.05), among which 17 GO terms and 21 KEGG pathways were associated with the formation of non-white wool. Screening in the white wool color group (G2 vs. G1) yielded 214 candidate genes, including ABCD4, VSX2, ITCH, NNT, POLA1, IGF1R, HOXA10, and DAO, which were associated with the formation of white wool; an enrichment analysis of the candidate genes revealed 9 significant GO-enriched pathways and 19 significant KEGG pathways (p < 0.05), including 5 GO terms and 12 KEGG pathways associated with the formation of white wool. In addition to furthering our understanding of wool color genetics, this research is important for breeding purposes.

Mouse Models of Human Proprotein Convertase Insufficiency

The kexin-like proprotein convertases perform the initial proteolytic cleavages that ultimately generate a variety of different mature peptide and proteins, ranging from brain neuropeptides to endocrine peptide hormones, to structural proteins, among others. In this review, we present a general introduction to proprotein convertase structure and biochemistry, followed by a comprehensive discussion of each member of the kexin-like subfamily of proprotein convertases. We summarize current knowledge of human proprotein convertase insufficiency syndromes, including genome-wide analyses of convertase polymorphisms, and compare these to convertase null and mutant mouse models. These mouse models have illuminated our understanding of the roles specific convertases play in human disease and have led to the identification of convertase-specific substrates; for example, the identification of procorin as a specific PACE4 substrate in the heart. We also discuss the limitations of mouse null models in interpreting human disease, such as differential precursor cleavage due to species-specific sequence differences, and the challenges presented by functional redundancy among convertases in attempting to assign specific cleavages and/or physiological roles. However, in most cases, knockout mouse models have added substantively both to our knowledge of diseases caused by human proprotein convertase insufficiency and to our appreciation of their normal physiological roles, as clearly seen in the case of the furin, proprotein convertase 1/3, and proprotein convertase 5/6 mouse models. The creation of more sophisticated mouse models with tissue- or temporally-restricted expression of specific convertases will improve our understanding of human proprotein convertase insufficiency and potentially provide support for the emerging concept of therapeutic inhibition of convertases.

Hypothalamic pathology in Huntington disease

Huntington's disease (HD), an autosomal dominant hereditary disorder associated with the accumulation of mutant huntingtin, is classically associated with cognitive decline and motor symptoms, notably chorea. However, growing evidence suggests that nonmotor symptoms are equally prevalent and debilitating. Some of these symptoms may be linked to hypothalamic pathology, demonstrated by findings in HD animal models and HD patients showing specific changes in hypothalamic neuropeptidergic populations and their associated functions. At least some of these alterations are likely due to local mutant huntingtin expression and toxicity, while others are likely caused by disturbed hypothalamic circuitry. Common problems include circadian rhythm disorders, including desynchronization of daily hormone excretion patterns, which could be targeted by novel therapeutic interventions, such as timed circadian interventions with light therapy or melatonin. However, translation of these findings from bench-to-bedside is hampered by differences in murine HD models and HD patients, including mutant huntingtin trinucleotide repeat length, which is highly heterogeneous across the various models. In this chapter, we summarize the current knowledge regarding hypothalamic alterations in HD patients and animal models, and the potential for these findings to be translated into clinical practice and management.

Transcription factor Creb3l1 regulates the synthesis of prohormone convertase enzyme PC1/3 in endocrine cells

Transcription factor cAMP responsive element-binding protein 3 like 1 (Creb3l1) is a non-classical endoplasmic reticulum stress molecule that is emerging as an important component for cellular homeostasis, particularly within cell types with high peptide secretory capabilities. We have previously shown that Creb3l1 serves an important role in body fluid homeostasis through its transcriptional control of the gene coding for antidiuretic hormone arginine vasopressin in the neuropeptide-rich magnocellular neurones of the supraoptic nucleus. In response to osmotic stimuli such as dehydration, vasopressin magnocellular neurones undergo remarkable transcriptome changes, including increased Creb3l1 expression, to ensure that the supply of vasopressin meets demand. To determine where else Creb3l1 fits into the secretory cell supply chain, we performed RNA-sequencing of Creb3l1 knockdown anterior pituitary mouse corticotroph cell line AtT20. The target chosen for further investigation was Pcsk1, which encodes proprotein convertase enzyme 1 (PC1/3). PC1/3 is crucial for processing of neuropeptides and peptide hormones such as pro-opiomelanocortin (POMC), proinsulin, proglucagon, vasopressin and oxytocin. Viral manipulations in supraoptic nuclei by over-expression of Creb3l1 increased Pcsk1, whereas Creb3l1 knockdown decreased Pcsk1 expression. In vitro promoter activity and binding studies showed that Creb3l1 was a transcription factor of the Pcsk1 gene binding directly to a G-box motif in the promoter. In the dehydrated rat anterior pituitary, Creb3l1 and Pcsk1 expression decreased in parallel compared to control, supporting our findings from manipulations in AtT20 cells and the supraoptic nucleus. No relationship was observed between Creb3l1 and Pcsk1 expression in the neurointermediate lobe of the pituitary, indicating a different mechanism of PC1/3 synthesis by these POMC-synthesising cells. Therefore, Creb3l1, by regulating the expression of Pcsk1, does not control the processing of POMC peptides in the intermediate lobe.

Hypothalamic Alterations in Neurodegenerative Diseases and Their Relation to Abnormal Energy Metabolism

Neurodegenerative diseases (NDDs) are disorders characterized by progressive deterioration of brain structure and function. Selective neuronal populations are affected leading to symptoms which are prominently motor in amyotrophic lateral sclerosis (ALS) or Huntington’s disease (HD), or cognitive in Alzheimer’s disease (AD) and fronto-temporal dementia (FTD). Besides the common existence of neuronal loss, NDDs are also associated with metabolic changes such as weight gain, weight loss, loss of fat mass, as well as with altered feeding behavior. Importantly, preclinical research as well as clinical studies have demonstrated that altered energy homeostasis influences disease progression in ALS, AD and HD, suggesting that identification of the pathways leading to perturbed energy balance might provide valuable therapeutic targets Signals from both the periphery and central inputs are integrated in the hypothalamus, a major hub for the control of energy balance. Recent research identified major hypothalamic changes in multiple NDDs. Here, we review these hypothalamic alterations and seek to identify commonalities and differences in hypothalamic involvement between the different NDDs. These hypothalamic defects could be key in the development of perturbations in energy homeostasis in NDDs and further understanding of the underlying mechanisms might open up new avenues to not only treat weight loss but also to ameliorate overall neurological symptoms.

Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases?

There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.

Hypothalamic alterations in Huntington's disease patients: comparison with genetic rodent models

Unintended weight loss, sleep and circadian disturbances and autonomic dysfunction are prevalent features of Huntington's disease (HD), an autosomal dominantly inherited neurodegenerative disorder caused by an expanded CAG repeat sequence in the HTT gene. These features form a substantial contribution to disease burden in HD patients and appear to be accompanied by a number of neuroendocrine and metabolic changes, pointing towards hypothalamic pathology as a likely underlying mechanism. Neuronal inclusion bodies of mutant huntingtin, which are hallmarks of the disease, occur throughout the hypothalamus, and indicate local mutant huntingtin expression that could interfere with hypothalamic neuropeptide production. Also, several genetic rodent models of HD show features that could be related to hypothalamic pathology, such as weight loss and circadian rhythm disturbances. In these rodents, several hypothalamic neuropeptide populations are affected. In the present review, we summarise the changes in genetic rodent models of HD for individual hypothalamic nuclei, compare these observations to the hypothalamic changes that occur in HD patients, and make an inventory of the work that still needs to be done. Surprisingly, there is only limited overlap in the hypothalamic changes reported in HD patients and genetic rodent models. At present, the only similarity between the hypothalamic alterations in HD patients and genetic rodent models is a decrease in the number of orexin-expressing neurones in the lateral hypothalamus. Possible reasons for these discrepancies, as well as potential consequences for the development of novel therapeutic strategies, are discussed.