Development and Validation of a Job Exposure Matrix for Physical Risk Factors in Low Back Pain

Objectives

The aim was to construct and validate a gender-specific job exposure matrix (JEM) for physical exposures to be used in epidemiological studies of low back pain (LBP).

Materials and Methods

We utilized two large Finnish population surveys, one to construct the JEM and another to test matrix validity. The exposure axis of the matrix included exposures relevant to LBP (heavy physical work, heavy lifting, awkward trunk posture and whole body vibration) and exposures that increase the biomechanical load on the low back (arm elevation) or those that in combination with other known risk factors could be related to LBP (kneeling or squatting). Job titles with similar work tasks and exposures were grouped. Exposure information was based on face-to-face interviews. Validity of the matrix was explored by comparing the JEM (group-based) binary measures with individual-based measures. The predictive validity of the matrix against LBP was evaluated by comparing the associations of the group-based (JEM) exposures with those of individual-based exposures.

Results

The matrix includes 348 job titles, representing 81% of all Finnish job titles in the early 2000s. The specificity of the constructed matrix was good, especially in women. The validity measured with kappa-statistic ranged from good to poor, being fair for most exposures. In men, all group-based (JEM) exposures were statistically significantly associated with one-month prevalence of LBP. In women, four out of six group-based exposures showed an association with LBP.

Conclusions

The gender-specific JEM for physical exposures showed relatively high specificity without compromising sensitivity. The matrix can therefore be considered as a valid instrument for exposure assessment in large-scale epidemiological studies, when more precise but more labour-intensive methods are not feasible. Although the matrix was based on Finnish data we foresee that it could be applicable, with some modifications, in other countries with a similar level of technology.     

Structural basis for stem cell factor-KIT signaling and activation of class III receptor tyrosine kinases

Stem cell factor (SCF) binds to and activates the KIT receptor, a class III receptor tyrosine kinase (RTK), to stimulate diverse processes including melanogenesis, gametogenesis and hematopoeisis. Dysregulation of KIT activation is associated with many cancers. We report a 2.5 A crystal structure of the functional core of SCF bound to the extracellular ligand-binding domains of KIT. The structure reveals a 'wrapping' SCF-recognition mode by KIT, in which KIT adopts a bent conformation to facilitate each of its first three immunoglobulin (Ig)-like domains to interact with SCF. Three surface epitopes on SCF, an extended loop, the B and C helices, and the N-terminal segment, contact distinct KIT domains, with two of the epitopes undergoing large conformational changes upon receptor binding. The SCF/KIT complex reveals a unique RTK dimerization assembly, and a novel recognition mode between four-helix bundle cytokines and Ig-family receptors. It serves as a framework for understanding the activation mechanisms of class III RTKs.     

Recovery of Historically Contaminated Watercourse Polluted by the Chemical Wood Industry: EROD Activity in Fish as Biomarker

Despite outstanding process alterations over decades, pulp- and paper-mill-contaminated sediments and continuing exposure by the effluents may still have effects on biota. In this study, ecotoxicological impacts in the boreal watercourse were analyzed by measuring ethoxyresorufin-O-deethylase (EROD) induction from wild fish populations and from experimentally exposed fish. In order to assess the role of sediment-borne chemicals, juvenile rainbow trout (Oncorhynchus mykiss) were exposed in the laboratory to the surface sediments of Lake Vatianjärvi and Southern Lake Saimaa, both watercourses impacted by the chemical wood industry for approximately a century. Hepatic EROD activity was also measured from roach (Rutilus rutilus) and perch (Perca fluviatilis) caught in Lake Vatianjärvi. Increased EROD activity was not observed in wild fish caught in Lake Vatianjärvi nor in rainbow trout exposed to the sediment of Lake Vatianjärvi, but it was observed in rainbow trout exposed to the sediment of Southern Lake Saimaa, probably explained by critically high concentrations of retene. The results of both the laboratory and field study indicate the absence of EROD-inducing compounds of the previously heavily contaminated Lake Vatianjärvi.     

Seasonal survival of young and adult black grouse females in boreal forests

Direct demographical information from different populations of species in concern may reveal processes to target by management. We estimated seasonal survival rates using data from 253 individual females in a continuous population of black grouse Tetrao tetrix in Central Finland in 2005–2007. The information theoretic model selection included the effects of age class, ecological season, year, and their relevant interactions. We showed a clear difference in the survival of young and older females during late winter, a decrease in female survival during spring, and variation between the study years. The most frequent proximate mortality cause was avian predation, and the avian predation rate was highest in spring.     

Short- and long-term population dynamical consequences of asymmetric climate change in black grouse

Temporal asymmetry in patterns of regional climate change may jeopardize the match between the proximate and ultimate cues of the timing of breeding. The consequences on short- and long-term population dynamics and trends as well as the underlying mechanisms are, however, often unknown. Using long-term data from Finland, we demonstrate that black grouse (Tetrao tetrix) have responded to spring warming by advancing both egg-laying and hatching. However, early summer (the time of hatching) has not advanced, and chicks have to face colder post-hatching conditions. Demonstrating that these conditions are critical to post-hatching survival, we show that chicks are increasingly suffering higher mortality because they hatch too early. Consequently, breeding success and population size has severely declined over the past four decades. Finally, we modelled the impact of this particular climate change scenario on population dynamics and show that the mismatch can further explain the observed collapse of cyclic fluctuations. Because the evolutionary response of grouse is lagging behind the novel selective pressures, seasonally asymmetric climate change is likely to constitute an important determinant of future short- and long-term changes in the dynamics of black grouse populations.     

Prolonged increase in dietary phosphate intake alters bone mineralization in adult male rats

Excessive intake of dietary phosphate without the company of calcium causes serum parathyroid hormone (s-PTH) concentration to rise. We investigated the effect of a modest but prolonged increase in dietary intake of inorganic phosphate on the bone quantitative factors of mature male rats. Twenty Wistar rats were divided into two groups and fed a high-phosphate diet (1.2% phosphate) or a control diet (0.6% phosphate) for 8 weeks. In the beginning and at the end of the study period, femur and lumbar bone mineral density (BMD), bone mineral content and area were measured using DXA, s-PTH was analyzed from the blood sample, and after sacrifice, right femur was cut loose and processed into paraffin cuts. Bone diameter, inner diameter and cortical width was measured from the hematoxylin- and eosin-dyed femur cuts. Tibias were degraded and calcium and phosphate content was analyzed by inductively coupled plasma-mass spectrometer. Femoral BMD increased significantly more in the control group than in the phosphate group (P=.005). Lumbar BMD values decreased in both groups, and the fall was greater in the control group (P=.007). The phosphate group had significantly higher s-PTH values (P=.0135). Femoral histomorphometric values or tibial mineral contents did not differ between groups. In conclusion, increase in dietary phosphate intake caused s-PTH to rise and hindered mineral deposition into cortical bone, leading to lower BMD. The effect on trabecular bone was opposing as mineral loss was less in the lumbar spine of phosphate group animals. These results are in concurrence with the data stating that skeletal response to PTH is complex and site dependent.     

A Class III PDZ Binding Motif in the Myotilin and FATZ Families Binds Enigma Family Proteins: a Common Link for Z-Disc Myopathies

Interactions between Z-disc proteins regulate muscle functions and disruption of these interactions results in muscle disorders. Mutations in Z-disc components myotilin, ZASP/Cypher, and FATZ-2 (calsarcin-1/myozenin-2) are associated with myopathies. We report here that the myotilin and the FATZ (calsarcin/myozenin) families share high homology at their final C-terminal five amino acids. This C-terminal E[ST][DE][DE]L motif is present almost exclusively in these families and is evolutionary conserved. We show by in vitro and in vivo studies that proteins from the myotilin and FATZ (calsarcin/myozenin) families interact via this novel type of class III PDZ binding motif with the PDZ domains of ZASP/Cypher and other Enigma family members: ALP, CLP-36, and RIL. We show that the interactions can be modulated by phosphorylation. Calmodulin-dependent kinase II phosphorylates the C terminus of FATZ-3 (calsarcin-3/myozenin-3) and myotilin, whereas PKA phosphorylates that of FATZ-1 (calsarcin-2/myozenin-1) and FATZ-2 (calsarcin-1/myozenin-1). This is the first report of a binding motif common to both the myotilin and the FATZ (calsarcin/myozenin) families that is specific for interactions with Enigma family members.The sarcomere of striated muscle consists of strictly organized subunits, myosin-containing thick filaments and actin-containing thin filaments. The thin filaments are aligned and cross-linked at the Z-discs by a molecular complex in which α-actinin is one of the core structures. Since the contractile force is transduced via the Z-discs, this structure has special requirements. It must provide extensive stability and yet undergo modulation in response to external signals. The Z-discs also serve as important sensors of extracellular cues and mediators of cellular signals that result in various adaptive responses (37). Muscle cells are able to sense changes in their workload and adapt accordingly via complex signaling pathways, some involving calcium, since its level in muscle cells alters in response to nerve pulses and muscle contraction. Of special importance is calcineurin, a sarcomeric calcium/calmodulin-dependent phosphatase that can act as a sensor of change. It is involved in the regulation of genes affecting muscle differentiation and fiber-type specification (12, 13).The special role of the Z-discs is indicated by the fact that mutations in several Z-disc proteins can result in neuromuscular disorders and cardiomyopathies. For instance, myofibrillar myopathy (desmin-related myopathy), a disease characterized by sarcomere disintegration and accumulation of thin filament material, is caused by dominantly inherited missense mutations in Z-disc proteins: myotilin, filamin-C, and Z-band alternatively spliced PDZ motif-containing protein (ZASP, also named LIM domain-binding factor 3, Cypher, or Oracle) (42, 43, 52). Missense mutations in myotilin can also result in limb-girdle muscular dystrophy 1A and spheroid body myositis (10, 18), while mutations in ZASP/Cypher (8, 57), myopalladin or FATZ-2 (calsarcin-1/myozenin-2) have been found to be associated with dominant familial dilated (7, 50) or hypertrophic cardiomyopathy (33). ZASP/Cypher knockout mice display a severe form of congenital myopathy and die postnatally (58), whereas myotilin knockout mice are virtually normal (31), suggesting redundancy between the myotilin family members and indicating that dysfunctional myotilin is more harmful to muscle cells than loss of the protein.Myotilin (40), palladin (32, 34), and myopalladin (3) are homologous Z-disc proteins that form a novel family of immunoglobulin-domain-containing actin-binding proteins. Biochemical studies on the best-characterized family member, myotilin, have demonstrated an association with important components of the sarcomere: α-actinin (40), which is a core structural component of the Z-disc; filamins (15, 49); the proteins of the FATZ (calsarcin/myozenin) family (15); and actin (51). Myotilin is linked to signaling networks by binding to the ubiquitin ligases Murf-1 and Murf-2 (54) and indirectly via FATZ (calsarcin/myozenin). Experiments using myotilin fragments with dominant-negative effect have shown its critical involvement in sarcomere organization. Myotilin bundles and stabilizes actin effectively, which suggests a role for myotilin in the organization and maintenance of Z-disc integrity.The FATZ (calsarcin/myozenin) proteins form another Z-disc family with structural and signaling functions. The three homologous members—FATZ-1 (calsarcin-2/myozenin-1), FATZ-2 (calsarcin-1/myozenin-2), and FATZ-3 (calsarcin-3/myozenin-3)—are localized in the Z-disc binding not only to myotilin but also to filamins A, B, and C (15), telethonin (T-cap), α-actinin, ZASP/Cypher, and calcineurin (9, 11, 12, 47). The three FATZ (calsarcin/myozenin) proteins share high homology at their N and the C terminals and, in fact, the binding sites for a variety of proteins occur in these regions. It has been suggested that the FATZ (calsarcin/myozenin) family may play a role in contributing to the formation and maintenance of the Z-disc, as well as in cell signaling, since its members bind calcineurin. FATZ-1 (calsarcin-2/myozenin-1) and FATZ-3 (calsarcin-3/myozenin-3) are highly expressed in skeletal muscle fast-twitch fibers, whereas FATZ-2 (calsarcin-1/myozenin-2) is highly expressed in cardiac muscle slow-twitch fibers. Mice lacking FATZ-2 (calsarcin-1/myozenin-2) showed an increase in the level of calcineurin, as well as a concurrent increase in the percentage of slow-twitch fibers (13). A recent report shows that FATZ-1 (calsarcin-2/myozenin-1) knockout mice have reduced body weight and fast-twitch muscle mass without exhibiting muscle atrophy (14). It is noteworthy that they also have the ability to run longer distances than control mice, thus exhibiting endurance to exercise. In fact, thus far only actinin-3 knockout mice have displayed this phenotype of endurance to exercise. FATZ-1 (calsarcin-2/myozenin-1)-deficient mice show an increase in oxidative muscle fibers and a switch from fast-twitch to slow-twitch fibers due to an increase in NFAT activity, as well as the regulator of calcineurin 1-4 (RCAN1-4), resulting in the concomitant increase in calcineurin signaling. Both FATZ-1 (calsarcin-2/myozenin-1) and FATZ-2 (calsarcin-1/myozenin-2) can regulate calcineurin/NFAT activity, thus influencing the fiber type composition of skeletal muscle (14).ZASP/Cypher (Oracle) (8, 35, 57) belongs to the Enigma family of proteins, the members of which all have a N-terminal PDZ domain and one or more LIM domains at the C-terminal (48). To date, there are six isoforms of ZASP/Cypher, all of which contain an N-terminal PDZ domain and none or three C-terminal LIM domains. ZASP/Cypher also contains a third domain known as the ZM motif which can also be found in ALP and CLP-36 (23, 24). It interacts with two different regions of α-actinin-2; its PDZ domain binds to the C-terminal EH-hand region of α-actinin-2, whereas its ZM motif binds to the rod region of α-actinin-2 (2, 23). ZASP/Cypher colocalizes with α-actinin-2 in the Z-disc, whereas the LIM domains interact with and are phosphorylated by all six isoforms of protein kinase C (PKC α, β1, γ, ζ, δ, and ɛ). ZASP/Cypher is important for the stability of the Z-disc; in fact, ZASP/Cypher knockout mice die in the first 24 h after birth as a result of functional failure of striated muscles caused by disruption of the Z-disc during muscle contraction (58). The PDZ of ZASP/Cypher is a classical type I PDZ domain that binds to the C-terminal of α-actinin-2.To better understand the biology of the Z-disc and pathogenesis of muscle disorders, it is important to unravel the dynamic interplay of Z-disc components. In the present study, we demonstrate a novel PDZ domain-binding motif common to the myotilin and FATZ (calsarcin/myozenin) protein families. This domain mediates interaction with ZASP/Cypher in a phosphorylation-dependent manner and is also involved in targeting ZASP/Cypher.