Primary osteoarthritis (OA) is a late-onset, degenerative condition of synovial joints, and is the major cause of pain and disability in older persons. OA represents a significant disease burden and focus of research, especially as no disease-modifying therapies exist to manage the condition. The genetic influence to OA is complex and polygenic. The arcOGEN study, the most powerful genome-wide association study yet to investigate OA in humans, identified the 9q33.1 locus to be significantly associated with hip OA in females. TRIM32 lies within the 9q33.1 susceptibility locus and may have strong biological relevance to OA; it encodes a protein with E3 ubiquitin ligase activity. Sanger sequencing of TRIM32 in the youngest 500 female patients with hip OA from the arcOGEN study was performed to identify rare variants in TRIM32 that are associated with OA of the hip in females. Polymorphisms were identified in the proximal promoter, and 3’untranslated regions (3’UTR) of TRIM32 that are disproportionately represented in female patients with hip OA, compared to the control population. In vitro studies identified expression of TRIM32 in human femoral head cartilage; reduced expression of TRIM32 was also demonstrated in femoral head primary articular chondrocytes from patients with hip OA compared to control patients. Trim32 knockout resulted in increased aggrecanolysis in murine femoral head explants. Murine chondrocytes deficient in Trim32 also exhibited increased expression of markers of a mature chondrocyte phenotype in response to anabolic cytokine stimulation, and increased expression of markers of a hypertrophic chondrocyte phenotype upon catabolic cytokine stimulation. In vivo studies of joint degeneration in Trim32 knockout mice demonstrated increased cartilage degradation and tibial epiphyseal bone changes after surgically induced knee joint instability, compared to wild-type mice. Increased cartilage degradation and medial knee subchondral bone changes were also identified upon ageing of Trim32 knockout mice. These results further implicate TRIM32 in the genetic predisposition to OA, and indicate a role for TRIM32 in the joint degeneration evident in OA. These results support the further study of TRIM32 in the pathophysiology of OA and development of novel therapeutic strategies to manage OA.

The voltage-gated potassium channel Kv1.2 impacts membrane potential and therefore excitability of neurons. Expression of Kv1.2 at the plasma membrane (PM) is critical for channel function, and altering Kv1.2 at the PM is one way to affect membrane excitability. Such is the case in the cerebellum, a portion of the brain with dense Kv1.2 expression, where modulation of Kv1.2 at the PM can impact electrical activity of neurons and ultimately cerebellum-dependent learning. Modulation of Kv1.2 at the PM can occur through endocytic trafficking of the channel; however mechanisms behind this process in the brain remain to be defined. The goal of this dissertation was to identify and characterize modalities endogenous to the brain that influence the presence of Kv1.2 at the neuronal plasma membrane. Mass spectrometry (MS) was used to first identify interacting proteins and post-translational modifications (PTM) of Kv1.2 from cerebellar tissue, and the roles of these interactions and modifications on Kv1.2 function were evaluated in two studies: The first study investigated Trim32, a protein enzyme that catalyzes ubiquitylation, a PTM involved in protein degradation, but also in non-degradative events such as endocytic trafficking. Trim32 was demonstrated to associate and localize with Kv1.2 in cerebellar neurons by MS, immunoblotting (IB), and immunofluorescence (IF), and also demonstrated the ability to ubiquitylate Kv1.2 in vitro through purified recombinant proteins. Utilizing cultured cells through a combination of mutagenesis, biochemistry, and quantitative MS, a working model of Kv1.2 modulation was developed in which Trim32 influences Kv1.2 surface expression by two mechanisms that both involve cross-talk of ubiquitylation and phosphorylation sites of Kv1.2. The second study investigated WNK1, a chloride-sensitive kinase which regulates cellular homeostasis. Using MS, IB, and IF, WNK1 was demonstrated to associate and localize with Kv1.2 in the cerebellum, and a combination of mutagenesis and pharmacology in both wild-type and WNK1-knockout cultured cells produced a working model whereby WNK1 modulates surface Kv1.2. Activation of the downstream target SPAK kinase, also identified by MS to associate with Kv1.2 in the brain, by WNK1 was additionally found to influence the manner of WNK1 modulation of Kv1.2. In addition to providing new models of Kv1.2 modulation in the brain, these studies propose novel biological roles for Trim32 and WNK1 that may ultimately impact neuronal excitability.

Limb girdle muscular dystrophies (LGMDs) are a clinically and genetically heterogeneous group of myopathies characterized by weakness and wasting of the proximal musculature. There are currently seventeen loci associated with different LGMDs, seven with an autosomal dominant mode of inheritance (LGMD1A–1G) and 10 with an autosomal recessive mode of inheritance (LGMD2A– 2J). The cumulative worldwide prevalence of LGMD is thought to be ~1/15,000. In the Hutterite population of North America there is an over-representation of autosomal recessive LGMD with a prevalence estimated to be >1/400. The objective of this work was to delineate the genetic basis of LGMD in this large genetically isolated population. A genome-wide scan was performed on Hutterite LGMD patients and their families in order to locate the mutant gene. This allowed us to identify a novel locus at chromosome region 9q31-33 that was named LGMD2H. Extensive haplotyping and mutation screening led to the discovery of c.1459G>A in TRIM32 as the causative mutation of LGMD2H. We then found that this same mutation was the cause of another previously described myopathy in the Hutterites, sarcotubular myopathy (STM)[reference awaiting publishers decision]. Analysis of the TRIM32 gene product revealed that it is a potential E3-ubiquitin ligase, is expressed in many human tissues including muscle and brain, and has a punctate cytoplasmic distribution. During the analysis of the LGMD2H region, it became apparent that there were Hutterite LGMD patients not linked to the LGMD2H locus. In order to identify the causative gene(s) in the remaining families, we performed a genome-wide scan. A locus at chromosome 19q13 was found to correspond to disease inheritance, the site of a previously described LGMD locus, LGMD2I. No causative gene had yet been identified at this locus so haplotyping and mutation screening was performed. We were able to identify c.826C>A in FKRP as the causative mutation in our remaining cohort of LGMD patients. The same mutation has since been found in many other populations, and is apparently a relatively common cause of LGMD. We obtained DNA from 19 non-Hutterite LGMD2I patients of diverse origins with c.826C>A and determined that it is an old founder mutation. There is no further evidence of any other loci causing autosomal recessive myopathy in the Hutterites. With the identification of c.1459G>A in TRIM32 and c.826C>A in FKRP we appear to have delineated the genetic cause of all myopathies of increased prevalence in the Hutterite population. To date, we have been able to provide accurate, non-invasive, diagnosis to over 70 patients and have provided carrier testing to approximately 120 at-risk family members. This kind DNA-based approach is not feasible in the general population due the enormous amount of locus, allelic, and clinical heterogeneity among myopathy patients. / May 2005

Limb girdle muscular dystrophies (LGMDs) are a clinically and genetically heterogeneous group of myopathies characterized by weakness and wasting of the proximal musculature. There are currently seventeen loci associated with different LGMDs, seven with an autosomal dominant mode of inheritance (LGMD1A–1G) and 10 with an autosomal recessive mode of inheritance (LGMD2A– 2J). The cumulative worldwide prevalence of LGMD is thought to be ~1/15,000. In the Hutterite population of North America there is an over-representation of autosomal recessive LGMD with a prevalence estimated to be >1/400. The objective of this work was to delineate the genetic basis of LGMD in this large genetically isolated population. A genome-wide scan was performed on Hutterite LGMD patients and their families in order to locate the mutant gene. This allowed us to identify a novel locus at chromosome region 9q31-33 that was named LGMD2H. Extensive haplotyping and mutation screening led to the discovery of c.1459G>A in TRIM32 as the causative mutation of LGMD2H. We then found that this same mutation was the cause of another previously described myopathy in the Hutterites, sarcotubular myopathy (STM)[reference awaiting publishers decision]. Analysis of the TRIM32 gene product revealed that it is a potential E3-ubiquitin ligase, is expressed in many human tissues including muscle and brain, and has a punctate cytoplasmic distribution. During the analysis of the LGMD2H region, it became apparent that there were Hutterite LGMD patients not linked to the LGMD2H locus. In order to identify the causative gene(s) in the remaining families, we performed a genome-wide scan. A locus at chromosome 19q13 was found to correspond to disease inheritance, the site of a previously described LGMD locus, LGMD2I. No causative gene had yet been identified at this locus so haplotyping and mutation screening was performed. We were able to identify c.826C>A in FKRP as the causative mutation in our remaining cohort of LGMD patients. The same mutation has since been found in many other populations, and is apparently a relatively common cause of LGMD. We obtained DNA from 19 non-Hutterite LGMD2I patients of diverse origins with c.826C>A and determined that it is an old founder mutation. There is no further evidence of any other loci causing autosomal recessive myopathy in the Hutterites. With the identification of c.1459G>A in TRIM32 and c.826C>A in FKRP we appear to have delineated the genetic cause of all myopathies of increased prevalence in the Hutterite population. To date, we have been able to provide accurate, non-invasive, diagnosis to over 70 patients and have provided carrier testing to approximately 120 at-risk family members. This kind DNA-based approach is not feasible in the general population due the enormous amount of locus, allelic, and clinical heterogeneity among myopathy patients.

Limb girdle muscular dystrophies (LGMDs) are a clinically and genetically heterogeneous group of myopathies characterized by weakness and wasting of the proximal musculature. There are currently seventeen loci associated with different LGMDs, seven with an autosomal dominant mode of inheritance (LGMD1A–1G) and 10 with an autosomal recessive mode of inheritance (LGMD2A– 2J). The cumulative worldwide prevalence of LGMD is thought to be ~1/15,000. In the Hutterite population of North America there is an over-representation of autosomal recessive LGMD with a prevalence estimated to be >1/400. The objective of this work was to delineate the genetic basis of LGMD in this large genetically isolated population. A genome-wide scan was performed on Hutterite LGMD patients and their families in order to locate the mutant gene. This allowed us to identify a novel locus at chromosome region 9q31-33 that was named LGMD2H. Extensive haplotyping and mutation screening led to the discovery of c.1459G>A in TRIM32 as the causative mutation of LGMD2H. We then found that this same mutation was the cause of another previously described myopathy in the Hutterites, sarcotubular myopathy (STM)[reference awaiting publishers decision]. Analysis of the TRIM32 gene product revealed that it is a potential E3-ubiquitin ligase, is expressed in many human tissues including muscle and brain, and has a punctate cytoplasmic distribution. During the analysis of the LGMD2H region, it became apparent that there were Hutterite LGMD patients not linked to the LGMD2H locus. In order to identify the causative gene(s) in the remaining families, we performed a genome-wide scan. A locus at chromosome 19q13 was found to correspond to disease inheritance, the site of a previously described LGMD locus, LGMD2I. No causative gene had yet been identified at this locus so haplotyping and mutation screening was performed. We were able to identify c.826C>A in FKRP as the causative mutation in our remaining cohort of LGMD patients. The same mutation has since been found in many other populations, and is apparently a relatively common cause of LGMD. We obtained DNA from 19 non-Hutterite LGMD2I patients of diverse origins with c.826C>A and determined that it is an old founder mutation. There is no further evidence of any other loci causing autosomal recessive myopathy in the Hutterites. With the identification of c.1459G>A in TRIM32 and c.826C>A in FKRP we appear to have delineated the genetic cause of all myopathies of increased prevalence in the Hutterite population. To date, we have been able to provide accurate, non-invasive, diagnosis to over 70 patients and have provided carrier testing to approximately 120 at-risk family members. This kind DNA-based approach is not feasible in the general population due the enormous amount of locus, allelic, and clinical heterogeneity among myopathy patients.