Further research analyzing the impact of TG6 knock-out/inactivation in mHTT aggregation and disease development will finally elucidate the pathological relevance of our findings. Acknowledgments The authors wish to thank Rebecca Laura and Schnepf Glo?ner because of their technical assistance. Supplementary Materials Listed below are available online at https://www.mdpi.com/article/10.3390/ijms22168914/s1. Click here for extra data document.(1.8M, TNFRSF10D zip) Author Contributions Conceptualization, A.S.-K. assays. Our outcomes demonstrate the physical relationship between TG6 and (mutant) huntingtin by Olcegepant hydrochloride co-immunoprecipitation evaluation as well as the contribution of its enzymatic activity for the full total aggregate insert in SH-SY5Y cells. Furthermore, we see that TG6 appearance and activity are loaded in the olfactory tubercle and piriform cortex specifically, the regions exhibiting the highest quantity of mHTT aggregates in transgenic rodent types of HD. Furthermore, mHTT aggregates were colocalized within TG6-positive cells. These findings point towards Olcegepant hydrochloride a role of TG6 in disease pathogenesis via mHTT aggregate formation. gene was shown to cause spinocerebellar ataxia 35 (SCA35) [25,26,27]. Recently, TG6 variants were found to differ in patients suffering from Parkinsons disease, with the wildtype protein having a protective effect on cells by decreasing alpha-synuclein levels and enhancing autophagy . TGs share the common feature of catalyzing irreversible modifications on proteins, including the acyl-transfer between glutamines and lysines [10,16,29]. Under physiological conditions, this transamidation reaction is latent because of low free Ca2+ levels. In some pathophysiological conditions, e.g., HD, intracellular free Ca2+ may rise [30,31], thus favoring the crosslinking activity of TGs to the expenses of their GTP-binding function, which are mutually exclusive . Several authors have already shown Olcegepant hydrochloride that TG2 activity is increased in patients afflicted with Alzheimers disease (AD) and HD as compared to healthy subjects, which suggests that TG2 activity may contribute to the detrimental effects observed in affected individuals [33,34,35]. In support of this hypothesis, Tau protein, amyloid- peptide (A) and (m)HTT are theoretically excellent substrates for the activity of TGs [34,36,37], which would contribute to enhancing Olcegepant hydrochloride their propensity to aggregation. Nonetheless, the role of TG2 in neurodegenerative disorders is still a controversial subject of discussion [38,39,40,41]. The present study was undertaken to investigate expression, distribution and activity of TGs in the brain of HD transgenic animals [42,43]. We were particularly interested in analyzing the involvement of TG6, as this neuronal isoform is the least characterized in neurodegenerative disorders, yet it is the one abundantly expressed in the central nervous system. The results gathered in HD rodent models indicate a possible contribution of TG6 activity to the pathophysiology of HD. 2. Results 2.1. Regional Distribution of TG6 in BACHD Mice The BACHD mouse model was investigated for TG6 expression, as it represents a well-validated animal model of HD pathophysiology in which the full-length human mutant huntingtin protein is expressed . The distribution of TG6 was prominent and widespread in the brain of 12- and 68-week-old mice, displaying no obvious significant genotype- or age-dependent differences (Figure 1A). In general, the expression of the TG6 protein was highest in the cerebral cortex. Employing immunofluorescence analysis, TG6 distribution appeared to be homogeneously spread throughout the cytoplasm of cortical neurons in wt animals and the soma of larger pyramidal cells located in layers IV and V in the motor appeared more intensively immunolabeled in BACHD tg mice at older age, often displayed a characteristic ring-like (cytoplasmatic) staining pattern often in the periphery of nuclei (Figure 1A, arrowhead, cf. inlay in Figure 1A lower right panel). Open in a separate window Figure 1 TG6 expression is prominent in the cerebral cortex of BACHD mice. (A) Detection of TG6 (green) in the cortices of wildtype (wt) and transgenic (tg) (BACHD) mice by immunofluorescent labeling at 12 and 68 weeks of age. Arrowhead points to distinct TG6 expression pattern in old tg mice. Inlay was taken from the region indicated by the arrowhead. Scale bars: 5, 50 m. (B) In situ assay of TG6 enzymatic activity on cryosections of 12 months old BACHD mice. TG6 activity (green) of wt (center panel) and tg (right panel) animals was determined by incorporation of biotinylated TG6-specific peptide. Nuclei were counterstained using DAPI. Negative controls (NC, left panel) were obtained emitting CaCl2 in the incubation buffer. Scale bar: 100 m. 2.2. TG6 Enzymatic Activity Is Prominent in BACHD Olcegepant hydrochloride Mice To assess specific TG6 enzymatic activity in situ, we adapted a protocol described by Esposito and colleagues for intestinal tissue [44,45]. As presented in Figure 1B (NC), no or negligible background reactivity was detectable in the absence of CaCl2. Conversely, a.