Hedgehog regulates cerebellar progenitor cell and medulloblastoma apoptosis

The Role of Sonic Hedgehog Pathway in the Development of the Central Nervous System and Aging-Related Neurodegenerative Diseases

The Sonic hedgehog (SHH) pathway affects neurogenesis and neural patterning during the development of the central nervous system. Dysregulation of the SHH pathway in the brain contributes to aging-related neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. At present, the SHH signaling pathway can be divided into the canonical signaling pathway and non-canonical signaling pathway, which directly or indirectly mediates other related pathways involved in the development of neurodegenerative diseases. Hence, an in-depth knowledge of the SHH signaling pathway may open an avenue of possibilities for the treatment of neurodegenerative diseases. Here, we summarize the role and mechanism of the SHH signaling pathway in the development of the central nervous system and aging-related neurodegenerative diseases. In this review, we will also highlight the potential of the SHH pathway as a therapeutic target for treating neurodegenerative diseases.

Molecular Association of Medulloblastoma and Sarcoidosis: Case Report and Review of the Literature

BACKGROUND

Medulloblastoma (MB) is a malignant tumor of the central nervous system (CNS), and sarcoidosis is a chronic inflammatory disease of many organ systems, commonly affecting the lungs. No association between MB and sarcoidosis was described in the literature. MB and sarcoidosis have mutual molecular and signaling pathways that may predispose patients with sarcoidosis to develop MB. We describe a patient with sarcoidosis who developed MB.

CASE DESCRIPTION

The patient is a 36-year-old diagnosed with pulmonary sarcoidosis presented with ataxia, bilateral horizontal nystagmus, diplopia, and bilateral upper limb dysmetria was found to have a cerebellar mass on magnetic resonance imaging (MRI). He was initially treated with corticosteroids as a case of neurosarcoidosis. The patient's symptoms worsened, and repeat MRI showed an increase in the tumor size with hydrocephalus. External ventricular drain insertion plus midline suboccipital craniotomy and resection of the tumor was performed. Pathology revealed MB classic type, sonic hedgehog-activated. There was no cerebrospinal fluid dissemination. He received craniospinal radiation and chemotherapy. Follow-up 20 months after radiation revealed residual neurologic symptoms and no recurrence on MRI brain.

CONCLUSIONS

The exceedingly rare coexistence of adult MB and sarcoidosis may have a causal relationship based on specific common molecules. Leukotrienes, stimulation of astrocytes and Purkinje neurons, and the sonic hedgehog signaling pathway can be considered. Further genetic and molecular studies are merited.

Effects of corticosterone injections in mid-to-late mouse postnatal development on adult motor activity and coordination

Glucocorticoids are involved in the developing brain but, in excessive amounts, may depress its growth and cause psychomotor development disorders. To test the long-term vulnerability of motor structures such as the cerebellum to supraphysiological corticosterone (CORT), the hormone was subcutaneously delivered at a dose of 20 mg/kg from postnatal day (P) 8 to P29 in C57BL/6 male mice evaluated for sensorimotor functions at P15, P22, P29, and 3 months. Relative to placebo, CORT increased motor activity in the open-field at P29 and 3 months as well as facilitating rotorod acquisition and visuomotor control necessary for swimming towards a visible goal without affecting spatial learning in the Morris water maze. CORT caused lobule-specific effects on cerebellar morphology by decreasing granule cell layer thickness in simplex lobule but increasing molecular and granule cell layer thickness in crus 2. The functional impact of these changes is indicated by significant correlations found between cerebellar size and activity levels or proficiency on the rotorod test of motor coordination.

Deletion of Btg1 Induces Prmt1-Dependent Apoptosis and Increased Stemness in Shh-Type Medulloblastoma Cells Without Affecting Tumor Frequency

About 30% of medulloblastomas (MBs), a tumor of the cerebellum, arise from cerebellar granule cell precursors (GCPs) undergoing transformation following activation of the Sonic hedgehog (Shh) pathway. To study this process, we generated a new MB model by crossing Patched1 heterozygous (Ptch1^+/−) mice, which develop spontaneous Shh-type MBs, with mice lacking B-cell translocation gene 1 (Btg1), a regulator of cerebellar development. In MBs developing in Ptch1^+/− mice, deletion of Btg1 does not alter tumor and lesion frequencies, nor affect the proliferation of neoplastic precursor cells. However, in both tumors and lesions arising in Ptch1^+/− mice, ablation of Btg1 increases by about 25% the apoptotic neoplastic precursor cells, as judged by positivity to activated caspase-3. Moreover, although Btg1 ablation in early postnatal GCPs, developing in the external granule cell layer, leads to a significant increase of proliferation, and decrease of differentiation, relative to wild-type, no synergy occurs with the Ptch1^+/− mutation. However, Btg1 deletion greatly increases apoptosis in postnatal GCPs, with strong synergy between Btg1-null and Ptch1^+/− mutations. That pronounced increase of apoptosis observed in Ptch1^+/−/Btg1 knockout young or neoplastic GCPs may be responsible for the lack of effect of Btg1 ablation on tumorigenesis. This increased apoptosis may be a consequence of increased expression of protein arginine methyltransferase 1 (Prmt1) protein that we observe in Btg1 knockout/Ptch1^+/− MBs. In fact, apoptotic genes, such as BAD, are targets of Prmt1. Moreover, in Btg1-null MBs, we observed a two-fold increase of cells positive to CD15, which labels tumor stem cells, raising the possibility of activation of quiescent tumor cells, known for their role in long-term resistance to treatment and relapses. Thus, Btg1 appears to play a role in cerebellar tumorigenesis by regulating the balance between apoptosis and proliferation during MB development, also influencing the number of tumor stem cells.

Genome-wide chromatin accessibility and transcriptome profiling show minimal epigenome changes and coordinated transcriptional dysregulation of hedgehog signaling in Danforth's short tail mice

Danforth's short tail (Sd) mice provide an excellent model for investigating the underlying etiology of human caudal birth defects, which affect 1 in 10 000 live births. Sd animals exhibit aberrant axial skeleton, urogenital and gastrointestinal development similar to human caudal malformation syndromes including urorectal septum malformation, caudal regression, vertebral-anal-cardiac-tracheo-esophageal fistula-renal-limb (VACTERL) association and persistent cloaca. Previous studies have shown that the Sd mutation results from an endogenous retroviral (ERV) insertion upstream of the Ptf1a gene resulting in its ectopic expression at E9.5. Though the genetic lesion has been determined, the resulting epigenomic and transcriptomic changes driving the phenotype have not been investigated. Here, we performed ATAC-seq experiments on isolated E9.5 tailbud tissue, which revealed minimal changes in chromatin accessibility in Sd/Sd mutant embryos. Interestingly, chromatin changes were localized to a small interval adjacent to the Sd ERV insertion overlapping a known Ptf1a enhancer region, which is conserved in mice and humans. Furthermore, mRNA-seq experiments revealed increased transcription of Ptf1a target genes and, importantly, downregulation of hedgehog pathway genes. Reduced sonic hedgehog (SHH) signaling was confirmed by in situ hybridization and immunofluorescence suggesting that the Sd phenotype results, in part, from downregulated SHH signaling. Taken together, these data demonstrate substantial transcriptome changes in the Sd mouse, and indicate that the effect of the ERV insertion on Ptf1a expression may be mediated by increased chromatin accessibility at a conserved Ptf1a enhancer. We propose that human caudal dysgenesis disorders may result from dysregulation of hedgehog signaling pathways.

Humanin is a novel regulator of Hedgehog signaling and prevents glucocorticoid-induced bone growth impairment

Glucocorticoids (GCs) are frequently used to treat chronic disorders in children, including inflammation and cancer. Prolonged treatment with GCs is well known to impair bone growth, an effect linked to increased apoptosis and suppressed proliferation in growth plate chondrocytes. We hypothesized that the endogenous antiapoptotic protein humanin (HN) may prevent these effects. Interestingly, GC-induced bone growth impairment and chondrocyte apoptosis was prevented in HN overexpressing mice, HN-treated wild-type mice, and in HN-treated cultured rat metatarsal bones. GC-induced suppression of chondrocyte proliferation was also prevented by HN. Furthermore, GC treatment reduced Indian Hedgehog expression in growth plates of wild-type mice but not in HN overexpressing mice or HN-treated wild-type animals. A Hedgehog (Hh) antagonist, vismodegib, was found to suppress the growth of cultured rat metatarsal bones, and this effect was also prevented by HN. Importantly, HN did not interfere with the desired anti-inflammatory effects of GCs. We conclude that HN is a novel regulator of Hh signaling preventing GC-induced bone growth impairment without interfering with desired effects of GCs. Our data may open for clinical studies exploring a new possible strategy to prevent GC-induced bone growth impairment by cotreating with HN.-Zaman, F., Zhao, Y., Celvin, B., Mehta, H. H., Wan, J., Chrysis, D., Ohlsson, C., Fadeel, B., Cohen, P., Sävendahl, L. Humanin is a novel regulator of Hedgehog signaling and prevents glucocorticoid-induced bone growth impairment.

Loss of Tctn3 causes neuronal apoptosis and neural tube defects in mice

Tctn3 belongs to the Tectonic (Tctn) family and is a single-pass membrane protein localized at the transition zone of primary cilia as an important component of ciliopathy-related protein complexes. Previous studies showed that mutations in Tctn1 and Tctn2, two members of the tectonic family, have been reported to disrupt neural tube development in humans and mice, but the functions of Tctn3 in brain development remain elusive. In this study, Tctn3 knockout (KO) mice were generated by utilizing the piggyBac (PB) transposon system. We found that Tctn3 KO mice exhibited abnormal global development, including prenatal lethality, microphthalmia, polysyndactyly, and abnormal head, sternum, and neural tube, whereas Tctn3 heterozygous KO mice did not show abnormal development or behaviors. Further, we found that the mRNA levels of Gli1 and Ptch1, downstream signaling components of the Shh pathway, were significantly reduced. Likewise, neural tube patterning-related proteins, such as Shh, Foxa2, and Nkx2.2, were altered in their distribution. Interestingly, Tctn3 KO led to significant changes in apoptosis-related proteins, including Bcl-2, Bax, and cleaved PARP1, resulting in reduced numbers of neuronal cells in embryonic brains. Tctn3 KO inhibited the PI3K/Akt signaling pathway but not the mTOR-dependent pathway. The small molecule SC79, a specific Akt activator, blocked apoptotic cell death in primary mouse embryonic fibroblasts from Tctn3 KO mice. Finally, NPHP1, a protein with anti-apoptotic ability, was found to form a complex with Tctn3, and its levels were decreased in Tctn3 KO mice. In conclusion, our results show that Tctn3 KO disrupts the Shh signaling pathway and neural tube patterning, resulting in abnormal embryonic development, cellular apoptosis, and prenatal death in mice.

Targeting sonic hedgehog signaling in neurological disorders

Sonic hedgehog (Shh) signaling influences neurogenesis and neural patterning during the development of central nervous system. Dysregulation of Shh signaling in brain leads to neurological disorders like autism spectrum disorder, depression, dementia, stroke, Parkinson's diseases, Huntington's disease, locomotor deficit, epilepsy, demyelinating disease, neuropathies as well as brain tumors. The synthesis, processing and transport of Shh ligand as well as the localization of its receptors and signal transduction in the central nervous system has been carefully reviewed. Further, we summarize the regulation of small molecule modulators of Shh pathway with potential in neurological disorders. In conclusion, further studies are warranted to demonstrate the potential of positive and negative regulators of the Shh pathway in neurological disorders.

Mature salivary gland rests within sonic hedgehog-positive medulloblastoma: case report and insights into the molecular genetics and embryopathology of ectopic intracranial salivary gland analogs

Intracranial ectopic salivary gland rests within dural-based lesions are reported very infrequently in the literature. The authors report the unique case of a 12-year-old boy with a cerebellar medulloblastoma positive for sonic hedgehog (Shh) that contained intraaxial mature ectopic salivary gland rests. The patient underwent clinical and radiological monitoring postoperatively, until he died of disseminated disease. An autopsy showed no evidence of salivary glands within disseminated lesions. The intraaxial presence of salivary gland rests and concomitant Shh positivity of the described tumor point to a disorder in differentiation as opposed to ectopic developmental foci, which are uniformly dural based in the described literature. The authors demonstrate the characteristic "papilionaceous" appearance of the salivary glands with mucicarmine stain and highlight the role of Shh signaling in explaining the intraaxial presence of seromucous gland analogs. This article reports the first intraaxial posterior fossa tumor with heterotopic salivary gland rests, and it provides molecular and embryopathological insights into the development of these lesions.

Autocrine Sonic hedgehog signaling promotes gastric cancer proliferation through induction of phospholipase Cγ1 and the ERK1/2 pathway

Background

Sonic hedgehog (SHH) plays critical roles in cell growth and development. Tumor cells express SHH, which can promote cell proliferation and epithelial-to-mesenchymal transition. However, the autocrine SHH pathway has not been described in gastric cancer. The aim of this study was to explore molecular mechanisms underlying autocrine SHH signaling in gastric cancer cells.

Methods

SHH expression was assessed using immunohistochemistry and the results were compared with clinicopathologic parameters, including survival. Using gastric cancer cell lines, we measured SHH mRNA and protein expression, and studied the effects of SHH signaling on cell proliferation and SHH secretion. We also studied the effects of an inhibitor of PLC-γ1 on phosphorylation of phospholipase Cγ1 and extracellular signal-regulated kinases (ERK)1/2.

Results

SHH protein expression in gastric cancer tissue was significantly higher compared with that in normal gastric tissue (P < 0.001), and the increased expression was significantly associated with pT staging (P = 0.004), pN staging (P = 0.018), pM staging (P = 0.006), and pTNM staging (P < 0.001). In multivariate analyses, overall survival in gastric cancer was significantly shorter in cases with high SHH expression (HR = 1.734, 95 % CI: 1.109–2.713, P = 0.016). The AGS and SGC-7901 gastric cancer cell lines expressed SHH mRNA and protein. In these cell lines, SHH promoted carcinogenesis through activation of the PLCγ1-ERK1/2 pathway, resulting in increased cell proliferation and survival.

Conclusions

Increased SHH expression is associated with shorter survival in gastric cancer patients, and SHH could represent a useful biomarker or therapeutic target for this disease.